WO2017037211A1

WO2017037211A1 - Ceramic based printed circuit board and method for manufacturing such a printed circuit board

Info

Publication number: WO2017037211A1
Application number: PCT/EP2016/070678
Authority: WO
Inventors: Gerard CADAFALCH GAZQUEZ; Bahruz MAMMADOV; Johan EVERT TEN ELSHOF
Original assignee: Eurekite Holding B.V.
Priority date: 2015-09-04
Filing date: 2016-09-02
Publication date: 2017-03-09
Also published as: NL2015400B1

Abstract

A printed circuit board includes a substrate and a circuit. The substrate is a layer of a ceramic substance, and the circuit is arranged on at least one surface of the substrate. The layer of the ceramic substance includes a non-woven mat of particles of the ceramic substance, and the non-woven mat has a relative density of 25% or less in comparison with the bulk density of the ceramic substance. Also, the invention relates to a method for manufacturing such a printed circuit board.

Description

Ceramic based Printed Circuit Board and Method for manufacturing such a Printed Circuit Board

Description

Field of invention

The present invention relates to a ceramic based printed circuit board. Also, the invention relates to a method for manufacturing such a printed circuit board.

Background

Printed circuit board (PCB) technology is an essential part for electronics. A printed circuit board mechanically supports and electrically connects electronic components that are mounted on the printed circuit board. PCBs allow a more compact configuration of electronic devices and avoid the use of cables, which makes the assembly process easier and faster.

Moreover, PCB technology is also used to fabricate microstrips. Microstrip technology is used to convey microwave frequency radio signals to form antennas, couplers, filter, power dividers, etc. The advantage of microstrip to classic antenna design is space reduction and conformity.

In the prior art various types of printed circuit board are known based on the board material:

1. Glassfiber-plate printed circuit boards based on glassfibers embedded in a resin, typically epoxy resin;

2. Polymer based printed circuit boards based on a polymer foil;

3. Ceramic based printed circuit boards based on a ceramic substrate, and

4. Insulated metal substrate printed circuit boards.

Of these categories the ceramic based printed circuit board is predominantly used for highly demanding electronics such as power electronics or high frequency applications.

Electronic devices, especially power electronics, achieve high temperatures during operation. Certain applications such as automotive, aerospace or military, also require extreme working conditions. Moreover, during electronic assembly the PCB has to undergo high temperature cycles to solder the electronic elements.

High frequency applications also require a low dielectric loss to improve the electrical signal.

From US 2004/0247842 Al an electric circuit is known comprising an electronic substrate made from a porous material. The principal material in this regard is a fiber material such for example silica fiber or aluminia fiber or a ceramic material. The ceramic material offers an appropriate porous material with lightness in weight.

US 2003/0005723 Al describes a process for manufacturing a circuit substrate using inorganic material-based gel fine fibers.

There is an increasing demand for PCBs that are flexible to reduce size and weight of products, to allow more complex PCB configurations and allow flexibility in application.

Summary of invention

It is an object of the invention to overcome or mitigate the disadvantages of the printed circuit board from the prior art.

The object is achieved by a printed circuit board comprising a substrate and a circuit, the substrate being a layer of a ceramic substance, and the circuit being arranged on at least one surface of the substrate, wherein

the layer of the ceramic substance comprises a non- woven mat of particles of the ceramic substance, and the non- woven mat has a relative density of 25% or less in comparison with the bulk density of the ceramic substance, and wherein the particles of the ceramic substance include nano fibers with a diameter of 5 μιη or less.

In most cases the ceramic substance respective the non-woven mat only comprises nano fibers with the said diameter.

The invention is based on the observation that the weight of a solid ceramic substrate can be reduced strongly by replacing the solid substrate with a non- woven layer respective a non-woven mat of ceramic nanofibers since the density of the non-woven mat can be 10 % or less of the density of the solid.

The term non- woven mat according to the invention describes a layer with high flexibility and a non-woven structure in contrast to for example a fabric. Indeed the relative density of the said non- woven mat is about 1,4 g/cm³ or less whereas the bulk density of a technical ceramic material like for example zirconium oxide amounts to approximately 5 to 6 g/cm³. The respective density of the substrate is measured via the mass and the volume of the said material derived for example from displaced fluid. A comparable method is described in the aforementioned US 2003/0005723 Al (compare [0116]).

Additionally the substrate only consists of the said ceramic material because the substrate is a layer of ceramic substance comprising the non- woven mat. This means for example an additional binder material is not present at the fabricated product but can however be used during the process.

In addition to the reduction in weight, due to the porous structure, the non- woven structure of the ceramic substance offers substantially lower dielectric losses than a solid substrate of the same material, with a still a relatively high dielectric strength and low dielectric constant. Moreover, the porosity of the material also offers high thermal conductivity (value of air over value of ceramic).

Advantageously, it has been found that on the non-woven mat of ceramic nano fibers an electric circuit can be formed that adheres well to the surface of the non- woven mat.

As a result of the properties of the non-woven structure the printed circuit board according to the invention is highly flexible and can be folded or wrapped in any shape basically only limited by the circuit layer and components. This feature provides additional freedom of design in terms of required footprint for such a printed circuit board.

According to an aspect, the invention provides a printed circuit board as described above, wherein the ceramic substance is one selected from a group of ceramic substances comprising zirconia, yttrium stabilized zirconia, silicon-oxide, titanium-oxide, a silicate compound, a titanate compound and a nitride compound.

According to an aspect, the invention provides a printed circuit board as described above, wherein the density of the non-woven mat is about 1.4 g/cm³ or less.

According to an aspect, the invention provides a printed circuit board as described above, wherein the non- woven mat of the ceramic material has a dielectric loss of 75% of the dielectric loss of the ceramic material in bulk form, or less.

According to an aspect, the invention provides a printed circuit board as described above, wherein the circuit comprises a conductive patterned layer. According to an aspect, the invention provides a printed circuit board as described above, wherein the conductive patterned layer is one selected from a lithographically patterned layer, an inkjet-printed patterned layer, a screen-printed patterned layer, a laminated patterned layer and an electroplated patterned layer.

According to an aspect, the invention provides a printed circuit board as described above, wherein the circuit comprises a micro-strip transmission line element or an RFID element.

According to an aspect, the invention provides a printed circuit board as described above, wherein the circuit comprises a conductive connection pattern for components of an electrical or electronic circuit that are mounted on the printed circuit board.

According to an aspect, the invention provides a printed circuit board as described above, wherein the conductive patterned layer comprises one or more of silver, copper, nickel, platinum and their alloys.

Additionally, the invention relates to a method for manufacturing a printed circuit board comprising a substrate and a circuit layer, the substrate being a layer of a ceramic substance, the method comprising: - providing the layer of the ceramic substance as substrate; - creating the circuit layer on at least one surface of the substrate, wherein the layer of the ceramic substance comprises a non-woven mat of particles of the ceramic substance, and the non-woven mat has a relative density of 25% or less in comparison with the bulk density of the ceramic substance.

According to an aspect, the invention provides a method as described above, wherein the circuit layer comprises a conductive patterned layer and the creation of the circuit on the at least one surface comprises a process selected from a group comprising: inkjet-printing of the conductive patterned layer; screen-printing of the conductive patterned layer; lamination of the conductive patterned layer, and electroplating of the conductive patterned layer.

According to an aspect, the invention provides a method as described above, wherein the circuit comprises a conductive patterned layer and the creation of the circuit on the at least one surface comprises one process selected from a group comprising: creating a blanket conductive layer by means of one process selected from a group comprising: layer deposition, inkjet-printing, screen-printing, lamination, and electroplating, and subsequently processing by a lithographical patterning of the blanket conductive layer to form the conductive patterned layer.

According to an aspect, the invention provides a method as described above, further comprising: fabricating the non- woven mat of ceramic substance particles by a process selected from electrospinning, forcespinning and melt-blowing of a precursor of the ceramic substance.

According to an aspect, the invention provides a method as described above, wherein the ceramic substance is one selected from a group of ceramic substances comprising zirconia, yttrium stabilized zirconia, silicon-oxide, titanium-oxide, a silicate compound, a titanate compound and a nitride compound.

According to an aspect, the invention provides a method as described above, wherein the conductive patterned layer comprises one or more of silver, copper, nickel, platinum and their alloys.

Advantageous embodiments are further defined by the dependent claims.

Brief description of drawings

The invention will be explained in more detail below with reference to drawings in which illustrative non-limiting embodiments thereof are shown. The scope of the invention is only limited by the definitions presented in the appended claims.

Figures 1 and 2 show a cross-section and a top view, respectively, of a printed circuit board according to an embodiment of the invention.

Detailed description of embodiments

Figure 1 shows a cross-section of a printed circuit board according to an embodiment of the invention.

The present invention relates to a printed circuit board 10 that comprises as a substrate 20 a non-woven mat of a ceramic substance. On a surface of the non-woven mat at least one circuit layer 30 is arranged.

The non- woven mat typically comprises nano fibers (sometimes referred to as microfibers) of the ceramic substance. Nanofibers in this respect are defined as fibers with a diameter of 5 micrometer or less. Production of ceramic nanofibers can be done by any known technique, inter alia by electrospinning or forcespinning or melt-blowing techniques The nanofibers are processed in a manner that a non-woven mat of the nano fibers is created.

The nanofibers are arranged in a porous but cohesive network, which provides internal strength to the non-woven structure. The non-woven mat therefore has a stable shape.

Also, the cohesion of the network allows that the non-woven mat is flexible and can folded or wrapped without rupture.

The ceramic substance can be any ceramic material that can be produced in the shape of nanofibers.

For example, the ceramic substance can be selected from a group of materials comprising zirconia (zirconium-oxide), yttrium stabilized zirconia, titanium-oxide, titanate, silicon-oxide, silicate, or nitride. The skilled in the art will appreciate that the choice of the ceramic substance may not be limited to a ceramic material of this list.

Due to the porous network of nanofibers the density of the non- woven mat is low and can be about 25% or less of the bulk density of the ceramic substance. For example, the density of a zirconia based non-woven mat is about 1.4 g/cm³ or lower.

In a preferred embodiment, the non- woven mat is substantially free of a binder material. In particular, for applications of the non- woven mat at elevated temperature (i.e., at about 100°C or higher), binder material may be undesirable due to instability and/or decomposition at such temperature. It is observed that creation of the non-woven mat from ceramic nanofibers in absence of binder material can result in a ceramic substrate with sufficient cohesion and strength to be used as printed circuit board substrate. In this manner, the invention provides that the printed circuit board 10 comprising the non- woven mat 20 can be configured for stable operation at such elevated temperatures, for example at 100°C or higher.

On a surface of the non-woven mat 20, a conductive layer 30 is arranged that embodies a circuit layer. The conductive layer 30 comprises a conductive material, i.e., a metal or a conductive metal compound.

The circuit layer is typically patterned in accordance with a desired functionality of the printed circuit board.

The circuit layer is created on at least one surface of the non-woven mat by a deposition technique selected from a group comprising inkjet printing, screen printing, lamination, and electroplating. For example, the non- woven mat 20 may have a thickness between about 10 micrometer and one or more millimeter (~10 μιη to >1 mm).

The conductive material of the circuit layer can comprise one or more of silver, copper, nickel, platinum and their alloys, but is not limited to these materials.

It should be noted that due to the porosity of the substrate non-woven mat, the interface between the substrate and the circuit layer may display some roughness and intermixing.

Patterning of the created circuit layer can be done in any manner known for the selected deposition technique.

Figure 2 shows a schematic top view of a printed circuit board according to an embodiment of the invention. On the surface of the non-woven mat 20 of ceramic fibers, the patterned circuit layer 30 is arranged. It will be appreciated that for illustration the circuit layer 30 is only schematically patterned in an arbitrary shape. The patterned circuit layer 30 may comprise one or more patterned layer areas.

According to an embodiment, the patterned circuit layer 30 is a stand-alone circuit such as a micro-strip transmission line or an RFID (Radio -Frequency

IDentification) circuit.

In case of a micro-strip transmission line a further metallic backplane (not shown) is required on the surface of the non- woven mat that opposes the surface with the circuit layer 30.

According to an alternative embodiment, the patterned circuit layer 30 can be arranged as a conductive connection pattern for components (not shown) of an electric or electronic circuit that are mounted on the printed circuit board 10.

The printed circuit board of the present invention can be used as a free standing circuit board or be incorporated into a body (shape) of a device.

Moreover, due to the thermal properties of the ceramic nanofibers, the printed circuit board can advantageously be used in relatively high temperature applications, by embedding in a fire resistant resin body or package or even in a ceramic body or package to form high temperature sensors. Also, the thermal properties allow relatively high manufacturing temperatures, in particular, the application in the ceramic package would require relatively extreme temperature during manufacturing.

In comparison to prior art printed circuit boards, the printed circuit board according to the invention has some advantages: the printed circuit board is flexible and relatively light-weight due to the use of a non-woven mat of ceramic fibers. Moreover, the printed circuit board has a relatively higher heat dissipation and thermal stability. In addition, due to the low density of the substrate , the dielectric losses are significantly lower than for solid substrates from the prior art. As a result, the printed circuit board according to the invention can enhance applications in for example the fields of high frequency RF telecommunications, power electronics, energy storage (batteries), LED lighting and high temperature sensing.

The invention has been described with reference to the preferred embodiment. Obvious modifications and alterations will occur to the skilled in the art upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the invention as defined by the appended claims.

Claims

1. Printed circuit board comprising a substrate and a circuit wherein the substrate is a layer of ceramic substance and the circuit is arranged on at least one surface of the substrate, wherein the layer of ceramic substance comprises a non- woven mat of particles of the ceramic substance and the non-woven mat has a relative density of 25% or less in comparison with the bulk density of the ceramic substance, and wherein the particles of ceramic substance include nano fibers with a diameter of 5 μιη or less.

2. Printed circuit board according to claim 1 wherein the ceramic substance is one selected from a group of ceramic substances comprising zirconia, yttrium- stabilised zirconia, silicon oxide, titanium oxide, a silicate compound, a titanate compound and a nitride compound.

3. Printed circuit board according to claim 1 or claim 2 wherein the density of the non-woven mat is approximately 1.4 g/cm³ or less.

4. Printed circuit board according to any one of preceding claims wherein the non- woven mat of ceramic substance has a dielectric loss of 75% of the dielectric loss of the ceramic substance in bulk form, or less.

5. Printed circuit board according to any one of the preceding claims wherein during use the circuit comprises a conductive patterned layer.

6. Printed circuit board according to claim 4 or claim 5 wherein the conductive patterned layer is one selected from a lithographically patterned layer, an inkjet- printed patterned layer, a screen-printed patterned layer, a laminated patterned layer and an electroplated patterned layer.

7. Printed circuit board according to any one of preceding claims 4-6 wherein the circuit comprises a micro-strip transmission line element or an RFID.

8. Printed circuit board according to any one of preceding claims 4-6 wherein the circuit comprises a conductive connection pattern for components of an electrical or electronic circuit which are mounted on the printed circuit board.

9. Printed circuit board according to any one of preceding claims 5-8 wherein the conductive patterned layer comprises one or more of silver, copper, nickel, platinum and their alloys.

10. Printed circuit board according to any one of the preceding claims wherein during use the printed circuit board has a curved, folded or rolled up shape.

11. Method of producing a printed circuit board that comprises a substrate and a circuit layer, wherein the substrate is a layer of ceramic substance; wherein the method comprises: providing the layer of ceramic substance as substrate; creating the circuit layer on at least one surface of the substrate, wherein the layer of ceramic substance comprises a non-woven mat of particles of ceramic substance and the non-woven mat has a relative density of 25% or less in comparison with the bulk density of the ceramic substance.

12. Method according to claim 11 wherein the circuit layer comprises a conductive patterned layer and the creation of the circuit layer on at least one surface comprises a process selected from a group comprising: inkjet printing of the conductive patterned layer; screen printing of the conductive patterned layer; laminating of the conductive patterned layer; and electroplating of the conductive patterned layer.

13. Method according to claim 11 wherein the circuit comprises a conductive patterned layer and the creation of the circuit on at least one surface comprises a process selected from a group comprising: creating a blanket conductive layer by means of one process selected from a group comprising: layer deposition, inkjet printing, screen printing, lamination and electroplating; and subsequently processing by means of lithographical patterning of the blanket conductive layer to thus form the conductive patterned layer.

14. Method according to any one of preceding claims 11-13 comprising: fabricating the non-woven mat of particles of ceramic substance by a process selected from electrospinning, force-spinning and melt-blowing of a precursor of the ceramic substance.

15. Method according to any one of preceding claims 11-14 wherein the ceramic substance is one selected from a group of ceramic substances comprising zirconia, yttrium-stabilised zirconia, silicon oxide, titanium oxide, a silicate compound, a titanate compound and a nitride compound.