WO2018220072A1

WO2018220072A1 - Method and system for manufacturing a workpiece by providing for a tackiness of a mixture of material adapted to modify its electrical conductivity when exposed with electromagnetic radiation

Info

Publication number: WO2018220072A1
Application number: PCT/EP2018/064286
Authority: WO
Inventors: Gustaf MÅRTENSSON; Tord Karlin
Original assignee: Mycronic AB
Priority date: 2017-06-01
Filing date: 2018-05-30
Publication date: 2018-12-06

Abstract

A method for manufacturing a workpiece (100) is disclosed, comprising providing (805) a first chemical component adapted to modify its electrical conductivity by 106— 1016 times when exposed with electromagnetic radiation (E), and mixing (807) said first chemical component with a second chemical component. The second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture during mounting of an electronic component. The method further comprises providing (810) a layer (120) of said mixture on at least a portion of a workpiece (110), patterning (830) the layer of said mixture by exposing the layer with electromagnetic radiation so as to form a pattern of first regions (122) having a first electrical conductivity and of second regions (124) having a second electrical conductivity, mounting (840) the electronic component (140) on the layer of said mixture, and curing (850) the mixture. A workpiece and system is also disclosed.

Description

METHOD AND SYSTEM FOR MANUFACTURING A WORKPIECE BY PROVIDING FOR A TACKINESS OF A MIXTURE OF MATERIAL ADAPTED TO MODIFY ITS ELECTRICAL CONDUCTIVITY WHEN EXPOSED WITH ELECTROMAGNETIC RADIATION

Technical field

The present invention relates to a method for manufacturing a workpiece, and in particular a workpiece wherein electronic components are attached to a substrate by means of a patterned layer of a material. The material may be a mixture of two or more chemical components, wherein at least one

component is adapted to modify its electrical conductivity when exposed with electromagnetic radiation. The present invention also relates to such a workpiece and a system. Background

Surface Mount Technology (SMT) is a method wherein electronic

components are mounted or placed onto a surface of a printed wiring board (PWB) so as to form a printed circuit board assembly. The electronic components may be electrically and mechanically connected to electric contact pads of the PWB by means of e.g. a solder joint formed of reflowed solder paste. Conventionally, the solder paste may be provided on the PWB in the form of deposits that are screen printed onto the contact pads.

Today, there is a growing interest in smaller electronic components, more densely packed printed circuit board assemblies, higher volumes and higher throughput. Thus, there is a need for improved workpieces and methods for mounting electronic components onto a substrate.

Summary

It is an object of the present invention to provide an improved method for manufacturing a workpiece comprising a substrate having electrically conductive regions and mounted electronic components. Accordingly, the invention provides a manufacturing method and a workpiece having the features set forth in the independent claims. Advantageous embodiments of the invention are defined by the dependent claims. Hence, according to a first aspect a method for manufacturing a workpiece is provided. The method comprises providing a first chemical component adapted to modify its electrical conductivity by at least 10 times, such as for example 10⁶- 10¹⁶ times when exposed with electromagnetic radiation, and mixing the first chemical component with a second chemical component. The second chemical component may be added as an adhesive, thereby providing the mixture of material with a tackiness that may be sufficient for an electrical component (or other items to be mounted) to adhere to the workpiece during the mounting of the electrical component. The tackiness may for example be at least 0.05 N, such as for example 0.05-10 N. This range has been found sufficient in order for an electronic component to adhere to the layer of the mixture during the manufacturing process. The method may further comprise providing a layer of said mixture on at least a portion of a substrate and patterning the layer of said mixture by exposing the layer with electromagnetic radiation so as to form a pattern of first regions having a first electrical conductivity and of second regions having a second electrical conductivity. In some embodiments, the method may further comprise mounting the electronic component on the layer of said mixture and, optionally, curing the mixture. In some examples, the first regions may have an electrical conductivity in the range of 10² - 10⁸ S/cm and the second regions have an electrical conductivity in the range of 10^"16 - 10^"8 S/cm.

According to a second aspect, a workpiece is provided comprising a substrate and an electronic component attached to the substrate by means of a layer of a mixture of chemical components that is mixed and patterned according to the method of the first aspect.

By adding a second chemical component to the first chemical component, the tackiness or stickiness of the mixture, in comparison to the first component only, may be increased. In this way, an electronic component may adhere to the layer of said mixture of material during the mounting of the component onto a surface coated with a layer of the mixture of material. The second chemical component does not have to be adapted to change its conductivity when exposed with electromagnetic radiation. The tackiness or stickiness may be changed by the second chemical component both before treatment of the mixture, after baking or after curing. The stickiness or tackiness may be different at different steps of the manufacturing method. For example, the tackiness before and after the curing step may be different.

The change in electrical conductivity of the mixture may e.g. be induced, or at least be more substantial, at certain frequencies and

amplitudes of the electromagnetic radiation. In one example, ultraviolet light may be used to modify the conductivity. The electrical conductivity of the mixture of chemical components may deteriorate upon exposure to

electromagnetic radiation having a frequency and amplitude within certain ranges. However, it will be appreciated that the electrical conductivity in other examples may increase as the mixture of chemical components is exposed to a certain type of electromagnetic radiation.

The present aspects are based on the realization that a patterned layer with regions having a first conductivity and regions having a second

conductivity may be formed without selective deposition and/or removal of material of the layer. Instead, electromagnetic radiation, such as e.g. light, may be utilized to define electrically conductive patterns and structures directly in the layer of mixture of chemical components. Preferably, patterning techniques known from e.g. photolithography may be used when exposing the mixture of chemical components to a desired pattern. Such techniques may e.g. include the use of photo masks and direct printing or direct writing. The use of light (or electromagnetic radiation) allows for relatively fine pitch structures and features of the pattern to be defined, in particular as compared with prior art methods involving selective deposition of material, involving e.g. printing and plating and selective removal of material, involving e.g. etching. Further, by forming the pattern in the layer of mixture of chemical components by changing the electrical conductivity of the mixture of chemical components, regions having different electrical conductivity may be provided in the same, possibly continuous, layer. The initially provided layer of mixture of chemical components may hence be kept intact in terms of its extension on the substrate, without any need for removal of material to form the pattern. By omitting steps relating to definition of a pattern by selective removal of material the manufacturing of the workpiece may be simplified and cheaper. Thus, the resulting, finished workpiece may be provided without utilizing any material removal processes such as for example etching. Instead, the layer of the mixture, to which the components may adhere by means of the tackiness, may be intact or at least have the same extension as it was given when provided on the workpiece.

The first chemical component may be adapted to modify its electrical conductivity by 10 times or more when exposed with electromagnetic radiation. This contrast between exposed and non-exposed regions allow for a plethora of applications, such as logic circuits, printable electronics, contact structures for surface mount technology (SMT) products, etcetera. Higher contrasts, such as in the range of for example 10⁶ to 10¹⁶ times, may advantageously be used in SMT applications in which electrical components are mounted to printed wiring boards. In these cases, the layer of the mixture may form the printed wiring board itself, be provided in a layer on top of the printed wiring board, or in specific contact structures.

The second chemical component may be adapted to provide the mixture with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture during mounting of an electronic component. Further, the mixture may retain its tackiness, prior to curing, with a tack time of e.g. 4 h after deposition. By providing a mixture that retains its tackiness for a predetermined period of time, the components may be mounted during that time period. This may decrease the risk of the layer or mixture having a tackiness or stickiness less than desired when mounting the components, which in turn may reduce the risk that components are incorrectly mounted, for example that they do not adhere properly to the layer on the substrate, or that substrates which have previously been provided with a layer needs to be discarded due to a too low tackiness. By predetermined period of time may be understood a period of time sufficiently long for allowing components to be mounted thereon and proceed to the curing step. The predetermined period of time, during which the mixture may retain a desired tackiness, may e.g. be controlled or adjusted by addition of the third component. Accordingly, the type and amount of the added third component may be selected based on the desired predetermined period of time and/or degree of tackiness.

The mixture of chemical components may e.g. be provided in the form of a liquid, a spray, a paste or a film, and may have adhesive properties allowing it to adhere to the surface of the substrate or workpiece. The mixture of chemical components may also be applied to the substrate by means of e.g. spin coating or a doctor blade. The mixture of chemical components may also be referred to as "mixture", "mixture of materials" or "composite material" in the present disclosure.

The mixing may be performed at any step of the method. For example, the mixing of the chemical components may be performed beforehand, or just before the layer is provided. The mixing may also be performed later. For example, a layer of the first component may be provided on a substrate, and later the second chemical components or the third chemical component may be added or mixed in. In this way, not all areas or portions of the first chemical component may be mixed with the second or third chemical component. "Mixing" should in the present disclosure be interpreted as any way of combining or mixing two or more chemical components, partly or fully. For example, a particle embedded in a fluid may be considered mixed.

The mixture may also be referred to as a composite material, formed of a combination of different chemical components such as the first chemical component and the second chemical component.

The mixture may in some examples form a stretchable structure. Such a structure may for example be employed in stretchable electronics, enabling electronics to be integrated in e.g. plasters and other medical devices intended to be attached to body tissue.

Further, the mixture may be provided directly on a live material or live tissue, such as e.g. human or animal skin, which hence may be considered as a "workpiece" or substrate as used in the context of the present disclosure. This allows electric circuits or structures to be patterned or printed directly on the material or tissue. Specific applications may for example include the creating of RFID tags on farm animals or livestock. Other examples may include robotic skin, for which the present invention may be employed to create an electrically conductive pattern directly on (or in) a flexible and possibly stretchable "skin".

The curing of the mixture of chemical components should be

understood as an optional step of changing e.g. a mechanical or rheological characteristic of the mixture. In the curing the mixture of chemical

components may be hardened or toughened into a relatively solid layer that may be electrically and/or mechanically coupled to the substrate. The mixture of material may be described by a non-cured state and a cured state, wherein electrical conductivity preferably may be changed in the non-cured state rather than the cured state. In other words, the curing may result in the electric conductivity being fixed or at least less sensitive to exposure by electromagnetic radiation. Further, mechanical properties such as e.g.

hardness, viscosity and elasticity may differ between the non-cured state and the cured state. In some examples, the curing may result in the mixture of material transitioning from a liquid or viscous state to the solid state, or at least to a state having greater hardness, rigidity or viscosity. Alternatively, or additionally, the mixture of material may, during curing, undergo a reduction in tackiness or stickiness. The curing may e.g. involve a chemical process, which may be induced by exposure to heat, electromagnetic radiation and/or chemical agents. In one example, a reflow oven of the same type as used in reflow of solder paste in prior art surface mount technology may be used. In other examples, the layer of mixture of material is cured by means of exposure to electron beams, microwaves or ultraviolet light.

The mixture of material may comprise a certain tackiness or stickiness allowing for the electronic component to adhere to the substrate during manufacturing and in particular during handling until curing of the mixture of material. The mixture of material, and in particular the regions of the material to which the electric component is attached, may hence act as a glue or adhesive keeping the mounted component in the right position on the substrate. The tackiness may be adjusted in an additional processing step, such as e.g. a baking step. During curing, the mixture of chemical

components may be hardened or otherwise modified to provide a more fixed or permanent coupling between the electronic component and the substrate. The electronic component may e.g. be arranged on the substrate such that an electric and/or mechanical coupling is established between the component and the substrate by means of the layer of mixture of material. The component may e.g. be arranged such that a contacting portion of the component contacts a region of the mixture of material having a first conductivity so as to form an electrical connection with the substrate. Further, the component may be attached to a region having a second, preferably lower electrical conductivity so as to e.g. provide a mechanical and/or thermal connection to the substrate.

The present aspects are advantageous in that they provide alternative methods of providing electrical structures and components on substrates. The pattern in the mixture of material may e.g. be used to define conductive tracks on printed wiring boards and other substrates for which electrical

communication paths are required. Further, the mixture of material and its regions of different electrical conductivity may provide electrical, thermal and/or mechanical connection to other components. Examples of such connections may include electrical joints (e.g. replacing prior art solder joints), heat sinks and underfill. Other applications of the present aspects may concern electronic devices or printed circuits, wherein the regions of different electric conductivity may define circuits and electronic components, such as e.g. resistors, capacitors and inductors, which may be printed directly on the substrate.

Defining the pattern by means of electromagnetic radiation is advantageous in terms of resolution and pitch of the electrically conducting regions, as electromagnetic radiation may allow for a higher resolution and finer pitch as compared with e.g. screen printing of solder paste.

The patterning may allow for not using underfill before mounting the component. For example, underfill structures may be included in the created pattern on the work piece. Alternatively, the need for underfill may be reduced as the component may be at least partly embedded in a layer of mixture.

Further, there may be a possibility to omit the packaging of the component, as the die may be attached on the printed wire board directly. According to the present disclosure, the workpiece may be protected by the layer of mixture with good chemical and corrosion resistances.

There may also be a possibility to form resistors on the printed wire board itself. For example, both the conductive regions and some types of components (e.g. resistors and capacitors) can be directly written onto the substrate itself, i.e. both the conductive regions and at least some of the components themselves may be formed on (written onto) the layer of the substrate when creating a pattern by the exposure to light using mask writing technology or direct write.

Further, it is realized that the above aspects may be employed for manufacturing 3D structures. In these examples, a plurality of layers may be stacked on each other to form a desired structure. Each of the layers, or at least some of them, may be patterned individually to provide certain electrically conducting structures within the 3D structure. In other words, the sequence of steps discussed in connection with the above aspects may be repeated in a multi-layer fashion, or in a 3D printing fashion.The present inventive concept may be employed to form a or pattern live material or biological tissue, such as e.g. animal or human skin,

The mixture of materials or chemical components may be at least partly light transmitting or transparent, and in particular to light within a certain range of wavelengths. The ability to transmit light may be of particular interest in connection with e.g. photovoltaic applications, window panes and visual displays, wherein the patterned mixture of materials may be used to define e.g. electric components or conductive tracks.

The end product of the method according to the first aspect and the workpiece according to the second aspect may be a finished printed circuit board assembly or circuit card assembly, i.e., a substrate (such as e.g. a printed wiring board comprising conductive pads) populated with electronic components. In one example, the majority of the electric components, or substantially all components, may be assembled in the method according to the present embodiment. Such a method may differ from a repair process wherein only one or a few components are repaired on, or added to, an already assembled circuit card assembly. The term "conductive" may, in the context of the present application, refer to a capability of a region of the mixture of chemical components to conduct or transmit a desired electrical power or signal, e.g. required for operation of an electronic component. The electrical power or signal may be transmitted in a direction parallel to the layer of mixture of chemical

components and/or in a direction substantially orthogonal to the layer. The first electrical conductivity may refer to such conductive regions, whereas the second electrical conductivity may refer to regions having reduced electric conductivity or even non-conductive regions, i.e., regions of the mixture of chemical components not being able to transmit or convey such an electrical power or signal.

A "first chemical component" should herein be understood as any type of material, component, element or compound suitable for being provided as a layer on a substrate or as a film. The second chemical component may be any type of material, component, element or compound suitable to be mixed with the first chemical component so that the tackiness or stickiness of the resulting mixture may be increased compared to the tackiness of the first chemical component itself. The third chemical component may be adapted to, when mixed with the first chemical component alone or with a mixture of the first and second chemical components, increase the electrical conductivity of the mixture.

According to an embodiment, the second chemical component may comprise at least one substance among the group of polymer resin, thermosetting polymer, thermoplastic resin, epoxy, cyanate ester, silicone, polyurethane, phenolic epoxy, acrylic, or polyimide, or a combination thereof.

Adding a second chemical component as an adhesive to the mixture allows for a stronger mechanical adhesion, which may work for all sizes of components. In other words, it does not need to be adapted specifically for different types or sizes of components or packages. In the mixture the adhesive strength can be tuned to match application requirements depending on the type and amount of the third chemical component mixed in the mixture.

According to one embodiment, the mixture may have a tackiness of 0.05-10 N prior to curing in order for the electronic component to adhere to the layer of mixture when the substrate, with the coated layer having said electronic component mounted thereon, is exposed to an acceleration above 0.5 gn. 0.5 gn may also be expressed as 0.5 G as a perceived force or weight depending on mass.

When the mixture, and thereby the layer of mixture, has a certain tackiness or stickiness, the electronic components may adhere to the substrate during manufacturing and in particular during handling until curing of the mixture of chemical components. The tack time here, in which the tackiness of the layer of mixture e.g. may not change by more than 50% prior to curing, may e.g. exceed 4 h. This may ease the handling of the workpiece during assembly, and thereby increase the throughput rate of the

manufacturing process. Further, it may reduce the need of a baking step, or of baking or curing the mixture. It will be realized that the electrical

components may be mounted in subsequent steps, without any baking or curing steps in-between. This may reduce the manufacturing time.

According to an embodiment, the curing of the mixture may comprise temperature treatment above 100 °C for at least 20 seconds of the mixture to thereby provide a shear strength for the mixture which is exceeding 5 MPa. That is, the mixture may be able to undergo a curing or a solidification that is thermally initiated. The thermal expansion of the mixture of chemical components may match that of the substrate on which it is layered.

As the solidification process or curing process has previously been performed at temperatures significantly higher than 100°C, having a mixture of chemical components that may be adapted to undergo curing by means of a temperature slightly above 100°C, lower processing temperatures are enabled and will thereby allow for the use of more sensitive components, as well as the use of plastic substrates for flexible boards.

According to an embodiment, the first chemical component may comprise at least one of organic monomers, photosensitive organic

monomers, organic polymers, photosensitive organic polymers, photo initiators, photosensitizers, photosensitive oxidants or reductants, photo acid or photo base generators, photosensitive dopants, metal oxides, graphite oxides or graphene oxides, or a combination thereof. According to an embodiment, the first chemical component may comprise graphite oxide, which may be arranged in a film and reduced into graphene in a process utilizing exposure to electromagnetic radiation. Such a reduction may e.g. be achieved by means of a flash reduction process in which graphite oxide may be photothernnally reduced upon exposure to e.g. a pulsed Xenon flash. The graphite oxide is advantageous in that it may be patterned by flashing through a photomask (or direct written by means of a light beam). Flash reduction is advantageous in that it is rapid, clean and versatile and may be done with a relatively simple equipment.

According to an embodiment, the first component is adapted to increase its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation of a wavelength within the wavelength range of 10-¹⁰ - 10-⁵ m.

In this way, the electrical conductivity can be controlled by which parts are exposed to electromagnetic radiation, and the workpiece may be patterned as desired.

According to an embodiment, the method may further comprise mixing said first chemical component and said second chemical component with a third chemical component comprising at least one substance among the group conductive fillers, metal particles, and carbon forms, or a combination thereof, and is adapted to change the electrical conductivity of exposed portions of said mixture of material 10⁸— 10¹⁸ times when exposed with electromagnetic radiation (E) of a wavelength within the wavelength range of 10^"10 - 10^"5 m.

For example, the second component may be one or more of

conductive fillers, metal particles in various shapes and sizes (e.g.

nano/micro-sized fibers, flakes, wires, spheres), or carbon in various sizes and shapes (e.g. nano/micro-sized graphite particles, graphene sheets, carbon nanotubes).

By adding a third chemical component to the first and second chemical components, the electrical conductivity of the mixture may be changed, both when exposed and not exposed by electromagnetic radiation. The third chemical component does not have to be configured to change its conductivity when exposed with electromagnetic radiation. Instead it can provide a general increase or shift of the electrical conductivity of the resulting mixture.

The increase or shift in electrical conductivity may be such that the conductivity of the mixtures is increased to a level where it is sufficiently conductive, that is, such that it is capable to conduct current at losses that are sufficiently low to be practically applicable in e.g. electronic devices. At the same time, the non-conductive portions, or portions of the mixture or layer with lower electrical conductivity, may have a sufficiently low conductivity so that they may act as electrical insulation. In this way, conductive paths or areas may be formed that are electrically separated or isolated by non- conductive, or low-conductivity, paths or areas.

The electrical conductivity before and after exposure to

electromagnetic radiation may be changed by adding a third chemical component to the mixture. In this way, the electrical conductivity of the mixture, compared to the first chemical component alone, may be increased by 10¹-10⁸ times. The mixture of chemical components may therefore change its electrical conductivity 10⁸ - 10¹⁸ times when exposed with e.g.

electromagnetic radiation. The difference in electrical conductivity between exposed and non-exposed regions may be at least 10-16 orders of magnitude. The difference may allow for forming conductive and non- conductive, or low conductive areas, wherein the non-conductive areas may act as insulation.

According to an embodiment, the electronic component may be mounted on an exposed region of the layer. Different parts of the electronic component may be mounted on different exposed or non-exposed regions of the layer. In this way, the electronic component can be mounted either where the electrical conductivity is relatively high or where it is relatively low. For example, one or more conductive portions of the electrical component may be mounted on one or more exposed areas such that electric current may pass through the component, between components, or such that the exposed area may act as an electrical component or a conductive track. According to an embodiment, the mixture may be subjected to one or several baking steps in which the mixture may be exposed to e.g. heat. The baking step(s) may e.g. be performed to achieve a desired viscosity or tackiness suitable for subsequent processing steps (such as e.g. mounting of components). It should be noted that baking of the mixture differs from curing, as the baking e.g. may be performed at temperatures lower than those required for curing and/or during periods of time too short to cure the mixture.

According to an embodiment, the regions having a first electrical conductivity may be electrically separated from, or isolated from, each other by regions having a second electrical conductivity. The regions having a first electrical conductivity may e.g. form electrical contact areas or terminals, or conductive tracks for transmitting e.g. electric power or signals. By separating the regions having the first electrical conductivity from each other by means of intermediate regions having less electrical conductivity the risk for electric shortcuts, electromagnetic crosstalk and losses may be reduced.

According to an embodiment, the regions having a first electrical conductivity may be formed so as to provide electrical connection to conductive pads, tracks and other conductive structures or features of the substrate. The regions having a first electrical conductivity may e.g. be formed directly on a conductive structure of the substrate so as to provide a stacked electrical contact structure. The regions having a first electrical conductivity may be formed so as to provide electrical connections between electronic components to be mounted on the substrate in a subsequent mounting step, or the regions may even be formed as to provide electrical connections between the conductive pads, e.g. to form a conductive path for conducting a current between the conductive pads, where the conductive path is extending on the surface of the coated substrate in a same plane as the layer of mixture on the substrate, and where the substrate e.g. is a printed wiring board used by the technology disclosed for manufacturing a workpiece in form of a printed circuit board. Additionally, the regions having the first electrical conductivity may extend beyond or outside of the conductive structure of the substrate, seen in a lateral direction of the substrate, so as to provide an electrical contact that is located beside the conductive structure of the substrate. The electrical contact may e.g. form part of a joint connecting an electronic component to the substrate. In one example, the regions having a first electrical conductivity may provide a wiring extending between an electrical contacting portion of the layer and a conductive pad or track of the substrate.

According to some embodiments, the step of patterning the layer of mixture of chemical component comprises exposing at least 50% of a total surface area of the layer at the same time. Preferably, the entire surface or substantially entire surface area may be patterned simultaneously so as to reduce the cycle time of the patterning step. Such an exposure may e.g. be performed by means of a photo mask.

According to an embodiment, the step of patterning the layer of mixture of chemical components comprises direct printing with e.g. laser.

According to an embodiment, the method further comprising forming an electronic device on the substrate. The electronic device may be defined by regions having different electrical conductivity so as to form e.g.

capacitors, inductors and resistors having a desired electrical performance or property. The electronic device may have a main current path extending in a same plane as the layer or in a direction perpendicular to the layer. The electric properties or performance of such an electronic device may e.g. be determined by a thickness of the layer of mixture of chemical components and/or the extent to which the mixture has been exposed.

Arranging the electronic device such that a current passes through the device in a direction orthogonal to the layer may be advantageous in terms of a reduced circuit area or footprint. Such an electronic device may e.g. be arranged between a mounted component and an underlying pad, thus having a footprint that at least partly overlaps with a footprint of the component. In one example, the electronic device forms a resistor extending between a surface of the layer of mixture of chemical components and an underlying pad. The resistance of the resistor may e.g. be determined by the thickness of the layer of mixture of chemical components and/or time and intensity of the exposure during the patterning of the layer. According to an embodiment, the substrate may be a printed wiring board for providing mechanical support and/or electrically connect e.g.

electronic components. The printed wiring board may e.g. comprise conductive tracks and contact portions (pads) arranged onto a non- conductive base of e.g. FR-4 glass epoxy. An assembled printed wiring board may be referred to as a printed circuit board assembly or circuit card assembly.

According to an embodiment, the mixture of chemical components may be viscous when provided on the substrate. The mixture of chemical components may in other words by applied to the substrate in a liquid state with a consistency allowing the mixture of chemical components to form a layer that remains on the substrate during subsequent processing steps. The term viscous should be understood as having a relatively thick and possibly sticky consistency or having a relatively high viscosity.

According to some embodiments, the layer of mixture of chemical components may be provided by means of spray coating or in the form of a film that is attached to the substrate.

According an embodiment, the layer of mixture of chemical

components may be provided so as to have a maximum thickness of 0.1 to 10.000 micrometers, such as a maximum thickness of 0.1 -200 micrometers. The thickness of the layer of mixture of chemical components may be varied so as to meet specific criteria regarding e.g. mechanical and electrical properties. A relatively thick layer may be advantageous in terms of mechanical attachment of e.g. electrical components, where a thicker layer may provide a better mechanical support for the components and/or their legs as compared to a thinner layer. On the other hand, a thinner layer may provide a reduced electrical resistance between the component and the substrate and be easier to bake and/or cure as compared to a thinner layer.

According to an embodiment, the layer of mixture of chemical components may be provided so as to have a thickness that varies by less than 10% of the intended layer thickness as seen over the surface of the substrate. The thickness may also vary by less than a predetermined interval, for example 5 micrometers. By reducing the variation in thickness, the mechanical and electrical performance of the layer may be improved in terms of reliability and predictability. Further, a relatively low variation in thickness (resulting in a relatively even and well defined surface) may facilitate subsequent processing of the substrate, such as e.g. mounting of

components, measurements and/or curing.

According to an embodiment, the step of patterning the layer may comprise exposing at least 90% of the total surface area of the layer at the same time.

According to an embodiment, the step of patterning the layer may comprise exposing the whole surface area of the layer at the same time.

According to an embodiment, the step of patterning the layer comprises exposing an area covering the whole surface area of the substrate provided with said layer, at the same time.

By "at the same time" it may be meant that the exposing is performed in the same step and in a short time period. Such an exposure may e.g. be performed by means of a photo mask.

By exposing an area of the layer provided on the surface, the time for the exposing step may be decreased in comparison to exposing smaller areas or the layer one at a time.

According to an embodiment, the step of providing the layer may comprise coating at least 70% of a total surface area of the in a single step.

According to an embodiment, the step of providing the layer comprises coating at least 90% of a total surface area of the substrate in a single step.

According to an embodiment, the step of providing the layer comprises attaching a film covering at least 90% of a total surface area of the substrate at in a single step.

According to an embodiment, the step of providing the layer comprises coating the whole surface area of the substrate in a single step.

The step of providing the layer of mixture may comprise sub steps. It is appreciated that the term "in a single step" may be refer to the case wherein there are no intermediate steps between the sub steps of providing the layer on the substrate. For example, the first component may be provided on the substrate and then the second component may be added. If there are no steps in-between the providing of the first chemical component and the second chemical component, or other sub steps of providing the layer, those may be considered to be consecutive, i.e. the providing of the layer of mixture is performed in one single step. If there are no sub steps in the step of providing the layer of mixture, in a single step may mean that the providing of the layer is performed one time only.

By providing the layer in a single step, the time for producing the workpiece may be reduced in comparison to performing the step of providing the layer at several points in time.

According to an aspect, a system for manufacturing a workpiece is provided. The system may comprise a coater, such as a spray coater, blade coater or spin coater, configured for providing a layer of a mixture of chemical components on at least a portion of a substrate. The mixture may comprise a first chemical component adapted to modify its electrical conductivity by at least 10 times, such as 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation, and a second chemical component, wherein the second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component. The system may further comprise a patterning tool, such as a photo mask writing tool or direct write tool, configured for patterning the layer by exposing the layer with electromagnetic radiation having a frequency and amplitude within the certain frequency range and amplitude range so as to form a pattern of first regions having a first electrical conductivity and second regions having a second electrical conductivity. The system may further comprise a mounting tool, such as e.g. a pick and place machine or die placement tool, configured for mounting an electronic component or die on the layer, and a curing tool, such as e.g. a reflow oven, electron beam generator, microwave unit or ultraviolet light unit, for curing the mixture.

According to aspects of the technology disclosed, a method is proposed where the step of mounting an electronic component on the layer of mixture of chemical components is omitted, the method may be defined by the following steps for manufacturing a workpiece 100:

providing a first chemical component adapted to modify its electrical conductivity by at least 10 times, such as 10⁶ - 10¹⁶ times, when exposed with electromagnetic radiation;

mixing said first chemical component with a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture during mounting of an electronic component;

providing a layer of said mixture on at least a portion of a substrate; patterning the layer of said mixture by exposing the layer with electromagnetic radiation so as to form a pattern of first regions having a first electrical conductivity and of second regions having a second electrical conductivity; and

curing the mixture, wherein said first regions have an electrical conductivity in the range of 10² - 10⁸ S/cm after said curing step and said second regions have an electrical conductivity in the range of 10^"16 - 10^"8 S/cm after said curing step.

The workpiece manufactured by the above proposed method may be a printed circuit board or a workpiece used for photovoltaic applications.

According to certain aspects of the technology disclosed, a system for manufacturing a workpiece is proposed where the mounting tool for mounting electronic components on the layer of mixture is omitted, the system is defined by the following units for manufacturing a workpiece:

a coater, such as a spray coater, blade coater or spin coater, configured for providing a layer of a mixture on at least a portion of a substrate, said mixture comprising a first chemical component adapted to modify its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation, and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component;

a patterning tool, such as a photo mask writing tool or direct write tool, configured for patterning the layer by exposing the layer with electromagnetic radiation having a frequency and amplitude within said certain frequency range and amplitude range so as to form a pattern of first regions having a first electrical conductivity and second regions having a second electrical conductivity; and

a curing tool, such as e.g. a reflow oven, electron beam generator, microwave unit or ultraviolet light unit, for curing the mixture.

The workpiece manufactured by the above proposed system may be a printed circuit board or a workpiece used for photovoltaic applications.

It will be appreciated that other embodiments than those described above are also possible. It will also be appreciated that any of the features in the embodiments described above for the method according to the first aspect of the present invention may be combined with the workpiece according to the second aspect of the present invention. Further objectives of, features of, and advantages with the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, in which:

figure 1 schematically depicts a cross sectional side view of a workpiece according to an embodiment of the present invention, comprising a substrate and a patterned layer of mixture of chemical components;

figures 2a-d schematically depict cross sectional side views of a workpiece according to an embodiment of the present invention, the side views illustrating the workpiece at different stages of the manufacturing process;

figures 3a and b schematically depict cross sectional side view of a workpiece according to an embodiment of the present invention, the workpiece having mounted components;

figure 4 schematically illustrates the layout of a prior art circuit having electrical components and separate resistors;

figures 5a-d and 6a-d schematically depict top views of workpieces at different stages of manufacturing processes according to embodiments of the present invention; and

figures 7a-d schematically depict cross sectional side views of a workpiece according to an embodiment of the present invention, the side views illustrating the workpiece at different stages of the manufacturing process;

figure 8 is an overview of a method for manufacturing a workpiece according to an embodiment;

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments of the present invention, wherein other parts may be omitted or merely suggested.

Detailed description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the invention to those skilled in the art. Furthermore, like numbers refer to the same or similar elements or components throughout.

With reference to figure 1 , there is shown a cross sectional side view of a workpiece 100 comprising a substrate 1 10 with and a layer 120 of a mixture of chemical components according to an embodiment of the present invention. The layer 120 of mixture of chemical components is provided on at least a portion of the substrate 1 10 and exposed by electromagnetic radiation, which is indicated by laser rays E in figure 1 , so as to form a pattern of regions 122 having a first conductivity and regions 124 having a second conductivity. As shown in the present figure, the regions 124 having a second conductivity may be defined or generated by the exposure to the

electromagnetic radiation E, whereas regions 122 of the layer 120 that are not exposed to the electromagnetic radiation E may be maintained in a state having the first conductivity.

The substrate 120 may, according to the present embodiment, comprise electrically conductive structures such as e.g. conductive pads 1 12 for electrical connection of e.g. electrical components (not shown in figure 1 ). The substrate 1 10 may in one example be printed wire board comprising e.g. FR-4 glass epoxy.

The layer 120 of a mixture of chemical components of two or more chemical components. One of the components, i.e. the first component, may comprise at least one of organic monomers, photosensitive organic

monomers, organic polymers, photosensitive organic polymers, photo initiators, photosensitizers, photosensitive oxidants or reductants, photo acid or photo base generators, photosensitive dopants, metal oxides, carbon based substances, carbon oxides, graphite oxides or graphene oxides, or a combination thereof. The first component may be mixed with a second chemical component so that the stickiness or tackiness of the mixture is increased.

The first chemical component may, for example, comprise a conductive polymer and an additive.

The second chemical component may increase the tackiness or stickiness of the mixture and thereby increate the tackiness or stickiness of the layer 120. The second chemical component may comprise polymer resin, thermosetting polymer, thermoplastic resin, epoxy, cyanate ester, silicone, polyurethane, phenolic epoxy, acrylic, or polymide or a combination thereof. The second component may be chosen such that the tackiness time is, for example, at least 4h, in order for the assembly to be completed. The mixture may be adapted to undergo curing or solidification that is thermally initiated. After curing, the material may have a shear strength that exceeds 5 MPa (potentially lower for flexible circuit boards, e.g. 0.5 MPa) and a thermal conductivity between 1-100 W/m K. The thermal expansion of the material may match that of the substrate on which it is layered.

The electrical conductivity of the mixture of chemical components, or only the first chemical component, may be changed, for example, by photo induced dedoping, photo conversion to increase the conductivity or photo conversion to decrease the conductivity.

For illustrative purposes only, a first component adapted for photo induced dedoping may be achieved with film of PEDOT/PSS-PBG

(PEDOT/PSS: poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate), PBG: 2-(9-Oxoxanthen-2-yl)propionic acid 1 ,5,7-triazabicyclo[4.4.0]dec-5-ene) prepared by spin coating and exposed with UV light (365 nm). Through the exposure, PBG converts to TBD (TBD: 1 ,5,7-triazabicyclo[4.4.0]dec-5-ene). TBD is a strong base that subsequently reacts with doped PEDOT7PSS^" to form neutral PEDOT⁰. Prior to exposure, the conductivity of the film is 800 S/cm. Following the exposure, the conductivity may be decreased to

1 .2x10^"3 S/cm.

Another illustrative example of a first chemical component adapted for photo conversion to decrease electrical conductivity is a polyaniline may be mixed with camphorsulfonic acid and combined with a photo initiator (e.g. cydohexylphenylketone). This first chemical component may be used in a 0.2 μιτι layer. The layer may undergo photo conversion upon exposure with UV light. Polyaniline is converted from its conductive emeraldine form (sheet resistance: 10³ Ωα) to its non-conductive leucoemeraldine form (sheet resistance: 10¹⁴ Ωα). This corresponds to a conversion in conductivity of 50 S/cm to 5x10^"10 S/cm.

A third example is of a first chemical component adapted for photo conversion to increase the electrical conductivity. An example is Poly(bis- alkylthioacetylene) (PATAC) This material may be used, for example, in a layer with a thickness of 1-10 μιτι on a substrate. The electrical conductivity of these films prior to exposure of electromagnetic radiation is 10^"14 S/cm; after irradiation with an Artie blue laser, the conductivity may increase to 80 S/cm.

According to a fourth example, the first chemical component may comprise graphite oxide, which may be arranged in a film from graphite powders prepared by e.g. Hummer's method. The patterning may e.g. be performed by means of a flash reduction process, in which e.g. flash energies of about 0.1 -2 J/cm² may be used in one or several flashes to reduce the graphite oxide into graphene.

Examples of first chemical components, such as conductive polymers, and additives may be found in table 1 below.

Photo exposure Conductive Additive Conductivity effect polymer change due to

exposure

Photoinduced PEDOT Photobase generator Decrease

dedoping (e.g. triazabicy- clodecene)

Photoconversion Polyaniline Photoinitiator (e.g. Decrease

cyclohexyl- phenylketone)

Photoconversion Poly(bis-alkylthio- Increase

acetylene)

Photoreduction Graphite oxide Increase

Table 1

In case of PEDOT, the conductivity change may be achieved by means of a photomask and irradiation of e.g. 25 minutes. If the first chemical compound comprises e.g. poly(bis-alkylthioacetylene), the increase in conductivity may be achieved by e.g. a laser scanning, in which a pattern may be formed scanning 600 mW with a speed of e.g. 5 cm/s. For the

photoreduction of graphite oxide as discussed above, several sequential light pulses may be used, wherein each of which may last for a few milliseconds. Optionally, a third chemical component may be mixed with the first and the second components, adapted to increase the conductivity of both exposed and non-exposed portions of the mixture.

The third component may, for example, be a conductive filler, metal particles or carbon-based substances. Examples include silver (Ag), gold (Au), nickel (Ni), copper (Cu) and carbon in various sizes and shapes. Among different metal particles, silver flakes may be beneficial because of the high conductivity, simple process for mixing and the maximum contact achieved. In addition, silver is unique among all the cost-effective metals by nature of its conductive oxide.

The layer 120 may be provided to at least partly cover at least the pads 1 12 of the substrate 1 10. It might be advantageous to use a layer 120 of mixture of chemical components that covers at least half the surface of the substrate 1 10, and preferably substantially the entire surface of the substrate 1 10. An electrical connection or path may be defined by regions 124 having a second conductivity, which in the present embodiment may be non- conductive so as to electrically separate the regions 122 having the first conductivity, i.e., regions being conductive. In the present example, conductive regions 122 may be provided above the pads 1 12 of the substrate 1 10 and defined by non-conductive regions 124 arranged at a periphery or perimeter of the pads 1 12. The layer 120 of mixture of chemical components may hence comprise a pattern of conductive regions 122 adapted to provide an electrical connection to the pads 1 12. The conductive regions 122 may be used in subsequent processing steps for mechanical and/or electrical connection of e.g. electrical components to the substrate 1 10.

It will be appreciated that the workpiece 100 depicted in figure 1 may relate to any substrate comprising a layer with electrically conductive and non-conductive regions. The substrate may e.g. form part of a photovoltaic application, window pane or visual display. Further, the layer of mixture of chemical components may be used for providing printed circuits, wherein the conductive and non-conductive regions of the pattern may define circuits and electronic components, such as e.g. resistors, capacitors and inductors, which may be printed directly on the substrate. Figure 2a-d show cross sectional side views of a workpiece 100 at different phases of a manufacturing process according to an embodiment of the present invention. The workpiece 100 may be similarly configured as the workpiece described with reference to figure 1 .

Figure 2a discloses a bare substrate, such as e.g. a printed wired board 1 10 having conductive pads 1 12 for providing an electrical connection to electronic components to be assembled.

In figure 2b, a layer 120 of a mixture as described above with reference to figure 1 has been provided. The layer of mixture be provided by means of spin coating, film deposition or spray coating. The layer 120 may have a thickness of e.g. 0.05 to 10.000 micrometers and may according to some embodiments be subjected to a baking step during which the mixture of chemical components may be exposed to e.g. heat. The baking step may e.g. be performed to achieve a desired viscosity or tackiness suitable for subsequent processing steps (such as e.g. mounting of components).

The layer 120 may then be provided with a pattern comprising electrically conductive regions 122 and electrically non-conductive regions 124. As shown in figure 2c, the conductive regions 122 may be separated with non-conductive regions 124 which may be provided by means of exposure to electromagnetic radiation. The transition of the mixture from a conductive state to a non-conductive (i.e. very low conductivity) state may e.g. be achieved by means of photo-oxidation of the material during exposure to UV-light during a predetermined period of time. The exposure to UV-light may induce photo-oxidation of the mixture of chemical components, which may result in a reduction in electrical conductivity.

The exposure may e.g. be performed by means of a photo mask 130 shown in figure 2c, wherein the entire surface of the layer 120 may be exposed in a single processing step. Alternatively, or additionally direct printing or scanning techniques may be used for defining the conductive regions 122 and the non-conductive regions 124.

As indicated in figure 2d, the conductive regions 122 may provide an electrical connection to underlying contact pads 1 12 of the substrate 1 10. Electronic components may be attached to the workpiece 100 in a subsequent step, e.g. by means of a pick and place tool (not shown in figure 2d) positioning the components at desired positions of the workpiece 100. The layer 120 may have a certain stickiness or tackiness allowing the components to adhere to the substrate 1 10 during the processing. The components may be permanently fixated to the substrate 1 10 in a curing step, e.g. by using a reflow tool similar to the tool used when reflowing solder paste in surface mount technology. In other examples, the layer is cured by means of exposure to chemical agents, electron beams, microwaves or ultraviolet light.

Figures 3a and b illustrates a similar workpiece as the embodiments discussed with reference to figures 1 and 2a-d. However, the workpiece 100 further comprises an assembled electronic component 140 that is attached to conductive regions 122 of the layer 120 of mixture of chemical components. Figure 3a discloses an electronic component, such as e.g. a resistor 140, having its contact portions directly attached to conductive regions 122 above the contact pads 1 12 of the substrate 1 10, whereas figure 3b discloses a component 140 that are fixated to the layer 120, and thus to the contact pads 1 12 of the substrate 1 10, by means of contact legs or balls 142 that are depressed into the conductive regions 122.

Figure 4 schematically depicts a prior art technology wherein mounted components 20 are electrically connected to resistive elements, such as resistors R, that are arranged at a distance from the components 20, such as e.g. beside the substrate 10. Such a layout is associated with a relatively high footprint or required surface area, and a relatively high cost.

Figures 5a-d illustrate the manufacturing of a workpiece according to an embodiment. The workpiece may be similarly configured as the

embodiments described with reference to figures 1 to 3.

Figure 5a is a top view of a substrate 1 10, such as e.g. a printed wiring board, comprising a plurality of contact pads 1 12. The substrate 1 10 may be provided with a layer 120 of a mixture of chemical components, as described above. The layer may e.g. be provided by spray coating or spin coating. In a subsequent step the layer 120 may be exposed so as to form a pattern of regions having different electrical conductivity (figure 5c). The regions may e.g. be non-conductive 124 and conductive 122, wherein the conductive regions 122 may be arranged at the contact pads 1 12 so as to allow for the substrate 1 10 to be electrically contacted by electronic components 140 (figure 5d).

Alternatively, or additionally, the layer 120 may comprise further regions provided with a certain electrical resistivity. Such regions may e.g. be used for providing electronic devices or functionalities that are integrated or direct printed in the layer 120 of mixture of chemical components. In one example, which will be described in the following, the layer 120 may comprise a conductive region, a non-conductive region and a region having an electrical conductivity between the non-conductive region and the conductive region. The conductivity may e.g. be determined by the exposure of the layer, wherein a longer exposure time or a higher exposure intensity (in case electromagnetic radiation is used) may result in a reduced conductivity. In certain aspects of the technology disclosed, the conductivity is determined in a plurality of exposures of a plurality of patterning steps, e.g. a double- exposure/patterning process where a first and second conductivity is determined by a first exposure to electromagnetic radiation and a third conductivity is determined in a second patterning step. Both the first and second patterning steps for exposing the substrate with electromagnetic radiation may expose substantially the entire surface of a substrate, where the first conductivity may represent non-conductive regions, the second conductivity may be an intermediate conductivity acting as resistors and the third conductivity may represent conductive tracks for conducting a current in the manufactured workpiece.

Figures 6a-d depict a workpiece that may be similarly configured as the embodiments discussed with reference to figures 1 -3 and 5.

Figures 6a and b disclose a substrate 1 10 having e.g. two contact pads 1 12 and a layer 120 of mixture of material. As shown in figure 6c, the layer 120 may be patterned with regions defining a non-conductive area 124, conductive areas 122 and an area 126 having a conductivity there between. The conductive areas 122 may be arranged at the contact pads 1 12, respectively, and electrically connected through the area 126 having the intermediate conductivity. The area 126 with the intermediate conductivity may in other words act as a resistor electrically arranged between the contact pads 1 12. As the components 140 are mounted to the substrate 1 10, an electric current is hence allowed to pass between the components via a resistive area 126 having a main current path in a plane parallel to the layer 120 of mixture of chemical components. By using the area 126 between two components 140 as an electronic device, such as e.g. a resistor, circuit size may be reduced.

Figures 7a-d show cross sectional side views of a workpiece according to an embodiment similarly configured as the embodiments described with reference to figures 1 -3, 5 and 6.

The workpiece may comprise a substrate 1 10 having two contact pads 1 12 that are interconnected by means of a conductive line 1 14. A layer 120 of mixture of chemical components may be provided by e.g. spin coating, film deposition or spray coating and patterned by means of electromagnetic radiation (figure 7b). The pattern may e.g. comprise non-conductive areas 124 defining two vias or contact regions 126 in the layer 120 above the contact pads 1 12, respectively (figure 7c). The contact regions 126 may be provided with an intermediate conductivity between the conductivity of the non-conductive areas 124 and the conductive areas 122 of the layer 120. The contact regions 126 may hence act a resistor arranged between the mounted component 140 (figure 7d) and the contact pad 1 12, wherein a main current path of such a resistor may be orthogonal to the layer 120. In other words, a resistor may be provided between the component 140 and the contact pad 1 12 so as to e.g. save space and allow for circuits having a reduced area.

Figure 8 schematically illustrates a method for manufacturing a workpiece that may be similarly configured as the embodiments described with reference to figures 1 -3 and 5-7.

The method may comprise the steps of providing a first chemical component 805, mixing 807 the first chemical component with a second chemical component, and optionally mixing 808 the first and second components with a third component. The first, second and third chemical components may be selected according to the examples discussed above in connection with any of the preceding embodiments. The method also comprises the steps of providing 810 a layer of the mixture on at least a portion of a substrate, baking 820 the layer so as to provide a desired hardness and/or tackiness, patterning 830 the layer by exposing the layer with electromagnetic radiation so as to form a pattern of regions having different electrical conductivity, mounting 840 electronic components to the layer o, and curing 850 the layer so as to fixedly secure the electronic components to the substrate.

In conclusion, a workpiece and a method for manufacturing such a workpiece is disclosed. The workpiece comprises a substrate, a layer of a mixture of chemical components and an electronic component, wherein the layer of mixture of chemical components is adapted, in a non-cured state, to change its electrical conductivity when exposed with electromagnetic radiation within a certain frequency and amplitude range. The layer of mixture thus comprises a pattern of regions having a first electrical conductivity and regions having a second electrical conductivity, and is adapted to attach the electronic component to the substrate.

While the present invention has been illustrated and described in detail in the appended drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. ITEMIZED LIST OF EMBODIMENTS

1 . A method for manufacturing a workpiece (100), comprising:

providing (805) a first chemical component adapted to modify its electrical conductivity by 10⁶— 10¹⁶ times when exposed with electromagnetic radiation (E);

mixing (807) said first chemical component with a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture during mounting of an electronic component;

providing (810) a layer (120) of said mixture on at least a portion of a substrate (1 10);

patterning (830) the layer of said mixture by exposing the layer with electromagnetic radiation so as to form a pattern of first regions (122) having a first electrical conductivity and of second regions (124) having a second electrical conductivity;

mounting (840) the electronic component (140) on the layer of said mixture; and

curing (850) the mixture, wherein said first regions (122) have an electrical conductivity in the range of 10² - 10⁸ S/cm after said curing step and said second regions (124) have an electrical conductivity in the range of 10^"16 - 10^"8 S/cm after said curing step. 2. The method according to embodiment 1 , wherein said second chemical component comprises at least one substance among the group of polymer resin, thermosetting polymer, thermoplastic resin, epoxy, cyanate ester, silicone, polyurethane, phenolic epoxy, acrylic, or polyimide, or a combination thereof.

3. The method according to any preceding embodiment, wherein the mixture has a tackiness of 0.05 - 10 N prior to curing in order for the electronic component to adhere to the layer of said mixture when said substrate, with said coated layer having said electronic component mounted thereon, is exposed to an acceleration above 0.5 gn.

4. The method according to any preceding embodiment, wherein the curing of the mixture is comprising temperature treatment above 100 °C for at least 20 seconds of the mixture to thereby provide a shear strength for the mixture which is exceeding 5 MPa.

5. The method according to any of the preceding embodiments, wherein said first chemical component is comprising at least one of organic

monomers, photosensitive organic monomers, organic polymers,

photosensitive organic polymers, photoinitiators, photosensitizers,

photosensitive oxidants or reductants, photoacid or photobase generators, photosensitive dopants, metal oxides, carbon oxides, graphite oxides, graphene oxides, or a combination thereof.

6. The method according to any of the preceding embodiments, wherein the first component is adapted to increase its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation (E) of a wavelength within the wavelength range of 10^"10 - 10^"5 m.

7. The method according to any of the preceding embodiments, further comprising:

mixing (808) said first chemical component and said second chemical component with a third chemical component comprising at least one substance among the group conductive fillers, metal particles, and carbon- based substances, or a combination thereof, and is adapted to change the electrical conductivity of exposed portions of said mixture of material 10⁸ - 10¹⁸ times when exposed with electromagnetic radiation (E) of a wavelength within the wavelength range of 10^"10 - 10^"5 m. 8. The method according to any of the preceding embodiments, wherein said electronic component (140) is mounted on an exposed region of said layer. 9. The method according to any preceding embodiment, further comprising a step of baking (820) the mixture so as to provide a desired hardness and/or tackiness of the layer.

10. The method according to any one of the preceding embodiments, wherein the regions having a first conductivity are formed so as to provide electrical connection between the electronic component and a conductive pad (1 12) of the substrate.

1 1 . The method according to any one of the preceding embodiments, wherein the step of patterning the layer is performed by means of a photo mask (130).

12. The method according to any one of the preceding embodiments, wherein the step of patterning the layer comprises exposing at least 50% of a total surface area of the layer at the same time.

13. The method according to embodiment 12, wherein substantially the entire surface area of the layer is exposed at the same time. 14. The method according to any one of the preceding embodiments, wherein the step of patterning the layer comprises direct printing.

15. The method according to any one of the preceding embodiments, further comprising a step of forming an electronic device (126) on the substrate, the electronic device being defined by regions having mutually different electrical conductivity. 16. The method according to embodiment 15, wherein the electronic device comprises a main current path extending in a same plane as the layer.

17. The method according to embodiment 15, wherein the electronic device comprises a main current path extending in a direction orthogonal to the layer.

18. The method according to any one of the preceding embodiments, wherein at least some of the regions exposed with said electromagnetic radiation define circuits and passive components in form of at least one of resistors, capacitors and inductors, which are thereby printed directly on the substrate.

19. The method according to any one of the preceding embodiments, wherein the substrate is a printed wiring board and the workpiece a printed circuit board assembly.

20. The method according to any one of the preceding embodiments, wherein the layer is provided by means of spray coating, a doctor blade or spin coating.

21 . The method according to any one of embodiments 1 to 19, wherein the layer is provided in the form of a film that is attached to the substrate. 22. The method according to any one of the preceding embodiments, wherein the layer is provided so as to have a maximum thickness of 1 to 200 micrometers.

23. The method according to any one of the preceding embodiments, wherein the layer is provided so as to have a thickness that varies less than 10% of the specified thickness as seen over the surface of the substrate. 24. The method according to any one of the preceding embodiments, wherein the step of patterning the layer comprises exposing at least 90% of the total surface area of the layer at the same time. 25. The method according to any one of the preceding embodiments, wherein the step of patterning the layer comprises exposing the whole surface area of the layer at the same time.

26. The method according to any one of the preceding embodiments, wherein the step of patterning the layer comprises exposing an area covering the whole surface area of the substrate provided with said layer, at the same time.

27. The method according to embodiment 20, wherein the step of providing the layer comprises coating at least 70% of a total surface area of the substrate in a single step.

28. The method according to embodiment 20, wherein the step of providing the layer comprises coating at least 90% of a total surface area of the substrate in a single step.

29. The method according to embodiment 21 , wherein the step of providing the layer comprises attaching a film covering at least 90% of a total surface area of the substrate in a single step.

30. The method according to embodiment 20, wherein the step of providing the layer comprises coating the whole surface area of the substrate in a single step. 31 . A workpiece (100) comprising a substrate (1 10), a layer (120) of a mixture and an electronic component (140), the layer being provided on at least a portion the substrate; wherein the mixture comprises a first chemical component adapted to modify its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation (E), and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component;

the layer comprises a pattern of first regions (122) having a first electrical conductivity and second regions (124) having a second electrical conductivity; and

the electronic component is attached to the substrate by means of the layer.

32. A system for manufacturing a workpiece (100), comprising:

a coater, such as a spray coater or spin coater, configured for providing (810) a layer (120) of a mixture on at least a portion of a substrate (1 10), said mixture comprising a first chemical component adapted to modify its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with

electromagnetic radiation (E), and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component;

a patterning tool, such as a photo mask writing tool or direct write tool, configured for patterning (830) the layer by exposing the layer with

electromagnetic radiation having a frequency and amplitude within said certain frequency range and amplitude range so as to form a pattern of first regions (122) having a first electrical conductivity and second regions (124) having a second electrical conductivity;

a mounting tool, such as e.g. a pick and place machine or die placement tool, configured for mounting (840) the electronic component or die (140) on the layer; and a curing tool, such as e.g. a reflow oven, electron beam generator, microwave unit or ultraviolet light unit, for curing (850) the mixture.

33. A method for manufacturing a workpiece (100), comprising:

providing (805) a first chemical component adapted to modify its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation (E);

patterning (830) the layer of said mixture by exposing the layer with electromagnetic radiation so as to form a pattern of first regions (122) having a first electrical conductivity and of second regions (124) having a second electrical conductivity; and

curing (850) the mixture, wherein said first regions (122) have an electrical conductivity in the range of 10²- 10⁸ S/cm after said curing step and said second regions (124) have an electrical conductivity in the range of 10^~16 - 10^"8 S/cm after said curing step.

34. A system for manufacturing a workpiece (100), comprising:

electromagnetic radiation (E), and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness prior to curing of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component; a patterning tool, such as a photo mask writing tool or direct write tool, configured for patterning (830) the layer by exposing the layer with

electromagnetic radiation having a frequency and amplitude within said certain frequency range and amplitude range so as to form a pattern of first regions (122) having a first electrical conductivity and second regions (124) having a second electrical conductivity; and

a curing tool, such as e.g. a reflow oven, electron beam generator, microwave unit or ultraviolet light unit, for curing (850) the mixture.

Claims

1 . A method for manufacturing a workpiece (100), comprising:

providing (805) a first chemical component adapted to modify its electrical conductivity by at least 10 times when exposed with electromagnetic radiation (E);

mixing (807) said first chemical component with a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness of 0.05- 10 N in order for an electronic component to adhere to the layer of said mixture during mounting of an electronic component;

providing (810) a layer (120) of said mixture on at least a portion of a workpiece (1 10);

mounting (840) the electronic component (140) on the layer of said mixture.

2. The method according to claim 1 , wherein said second chemical component comprises at least one substance among the group of polymer resin, thermosetting polymer, thermoplastic resin, epoxy, cyanate ester, silicone, polyurethane, phenolic epoxy, acrylic, or polyimide, or a combination thereof.

3. The method according to claim 1 or 2, further comprising curing (850) the mixture, wherein said first regions (122) have an electrical conductivity in the range of 10² - 10⁸ S/cm after the curing and said second regions (124) have an electrical conductivity in the range of 10^"16 - 10^"8 S/cm after the curing.

4. The method according to claim 3, wherein the curing of the mixture is comprising temperature treatment above 100 °C for at least 20 seconds of the mixture to thereby provide a shear strength for the mixture which is exceeding 5 MPa.

5. The method according to any of the preceding claims, wherein said first chemical component is comprising at least one of organic monomers, photosensitive organic monomers, organic polymers, photosensitive organic polymers, photoinitiators, photosensitizers, photosensitive oxidants or reductants, photoacid or photobase generators, photosensitive dopants, metal oxides, carbon oxides, graphite oxides, graphene oxides, or a combination thereof.

6. The method according to any of the preceding claims, wherein the first component is adapted to increase its electrical conductivity by 10⁶ - 10¹⁶ times when exposed with electromagnetic radiation (E) of a wavelength within the wavelength range of 10^"10 - 10^"5 m.

7. The method according to any of the preceding claims, further comprising:

mixing (808) said first chemical component and said second chemical component with a third chemical component comprising at least one substance among the group conductive fillers, metal particles, and carbon- based substances, or a combination thereof, and is adapted to change the electrical conductivity of exposed portions of said mixture of material 10⁸ - 10¹⁸ times when exposed with electromagnetic radiation (E) of a wavelength within the wavelength range of 10^"10 - 10^"5 m.

8. The method according to any of the preceding claims, wherein the first regions and the second regions of the mixture remain on the finished workpiece.

9. The method according to any one of the preceding claims, wherein the regions having a first conductivity are formed so as to provide electrical connection between the electronic component and a conductive pad (1 12) of the workpiece.

10. The method according to any one of the preceding claims, wherein the step of patterning the layer is performed by means of a photo mask (130).

1 1 . The method according to any one of the preceding claims, wherein the step of patterning the layer comprises direct printing.

12. The method according to any one of the preceding claims, further comprising a step of forming an electronic device (126) on the workpiece, the electronic device being defined by regions having mutually different electrical conductivity.

13. The method according to claim 12, wherein the electronic device comprises a main current path extending in a same plane as the layer.

14. The method according to claim 12, wherein the electronic device comprises a main current path extending in a direction orthogonal to the layer.

15. The method according to any one of the preceding claims, wherein at least some of the regions exposed with said electromagnetic radiation define circuits and passive components in form of at least one of resistors, capacitors and inductors, which are thereby printed directly on the workpiece.

16. The method according to any one of the preceding claims, wherein the layer is provided by means of spray coating, a doctor blade or spin coating.

17. The method according to any one of claims 1 to 15, wherein the layer is provided in the form of a film that is attached to the workpiece.

18. The method according to any one of the preceding claims, wherein the layer is provided so as to have a maximum thickness of 1 to 200 micrometers.

19. The method according to any one of the preceding claims, wherein the layer is provided so as to have a thickness that varies less than 10% of the specified thickness as seen over the surface of the workpiece.

20. A workpiece (100) comprising a substrate (1 10), a layer (120) of a mixture and an electronic component (140), the layer being provided on at least a portion the substrate; wherein

the mixture comprises a first chemical component adapted to modify its electrical conductivity by at least 10 times when exposed with electromagnetic radiation (E), and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture with a tackiness of 0.05-10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component;

the electronic component is attached to the substrate by means of the layer.

21 . A system for manufacturing a workpiece (100), comprising:

a coater configured for providing (810) a layer (120) of a mixture on at least a portion of a workpiece (1 10), said mixture comprising a first chemical component adapted to modify its electrical conductivity by at least 10 times when exposed with electromagnetic radiation (E), and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness of 0.05- 10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component; a patterning tool configured for patterning (830) the layer by exposing the layer with electromagnetic radiation having a frequency and amplitude within said certain frequency range and amplitude range so as to form a pattern of first regions (122) having a first electrical conductivity and second regions (124) having a second electrical conductivity; and

a mounting tool, such as e.g. a pick and place machine or die placement tool, configured for mounting (840) the electronic component or die (140) on the layer.

22. A method for manufacturing a workpiece (100), comprising:

providing (810) a layer (120) of said mixture on at least a portion of a workpiece (1 10); and

patterning (830) the layer of said mixture by exposing the layer with electromagnetic radiation so as to form a pattern of first regions (122) having a first electrical conductivity and of second regions (124) having a second electrical conductivity.

23. A system for manufacturing a workpiece (100), comprising:

a coater configured for providing (810) a layer (120) of a mixture on at least a portion of a workpiece (1 10), said mixture comprising a first chemical component adapted to modify its electrical conductivity by at least 10 times when exposed with electromagnetic radiation (E), and a second chemical component, wherein said second chemical component is added as an adhesive, thereby providing said mixture of material with a tackiness of 0.05- 10 N in order for an electronic component to adhere to the layer of said mixture of material during mounting of an electronic component; and

a patterning tool configured for patterning (830) the layer by exposing the layer with electromagnetic radiation having a frequency and amplitude within said certain frequency range and amplitude range so as to form a pattern of first regions (122) having a first electrical conductivity and second regions (124) having a second electrical conductivity.