WO2024094870A1

WO2024094870A1 - Sealed electrical devices

Info

Publication number: WO2024094870A1
Application number: PCT/EP2023/080708
Authority: WO
Inventors: Xu Shi; Shengfu ZHAO; Eric Jian Rong PHUA
Original assignee: Nanofilm Technologies International Limited; Schlich Ltd
Priority date: 2022-11-03
Filing date: 2023-11-03
Publication date: 2024-05-10

Abstract

The invention provides an electrical apparatus, the electrical apparatus comprising: at least first and second components, and an interface between the first and second components, wherein the apparatus further comprises: (a) a coating of ta-C at the interface to seal the interface against ingress and/or egress of fluids, or (b) a gasket at the interface, wherein the gasket comprises a coating of ta-C to seal the interface against ingress and/or egress of fluids The invention further provides a method of making an electrical apparatus.

Description

Sealed Electrical Devices

Introduction

The present invention relates to sealed electrical apparatuses I devices, and methods of making the same.

Background to the Invention

It is well known that electrical devices are sensitive to environmental factors, such as moisture and gases (e.g. oxygen). In many cases, the ingress of moisture and oxygen can lead to material degradation (e.g. via oxidation, ion migration and/or plasticisation mechanisms) and eventual failure of a device.

It is therefore important that moisture and gases are kept away from electrical and electronic devices susceptible to degradation as a result of environmental factors.

Certain electronic devices (such as hydrogen fuel cells) require internal flow of gases to function. However, it remains important that the gases are appropriately sealed in the relevant area of the device (i) to prevent degradation of fluid-vulnerable elements, and (ii) to prevent inefficiencies due to gas losses. Therefore, in many cases it is important to prevent egress of moisture and other fluids in addition to preventing ingress of the same.

Electronic devices, ranging from microelectromechanical systems (MEMS) to integrated circuits, need protection against moisture, oxygen, and various environmental factors that can harm their performance and durability. Traditional encapsulation methods, like epoxy molding or hermetic packaging, have limitations concerning their ability to withstand moisture, size restrictions, and cost implications. “Glob tops” are known to seal electronic devices - e.g. epoxies are dispensed onto electronic chips, but sealing issues remain.

Known barrier coatings often have multiple thin layers of metallised film, for example deposited by physical vapour deposition (PVD). Whilst these known barrier coatings may be able to impart good moisture and oxygen resistance, the coatings themselves are often susceptible to degradation and as such only retain their protective barrier functionality for a short period of time.

Alternative known coatings may use noble metals for long term barrier protection, however due to the cost of the materials, these coatings are prohibitively expensive for most applications.

Nanocomposite materials comprising two-dimensional nanomaterials in polymer layers have also been proposed as barrier coatings. However, again, these coatings are only able to provide short-term barrier protection since the nanocomposite material becomes saturated with penetrants over time.

Other electronic devices, however, are or comprise multilayer devices. Ingress of moisture and/or gases between (rather than through) the layers can lead to delamination of the layers, reducing the lifetime of the device.

US 2009/0252894 describes the use of silicon and oxygen-containing barrier coatings, 500nm thick in examples, to protect moisture sensitive LED devices.

JP 2005 173106 discloses electro-optical devices having a diamond-like carbon film covering certain components and located between certain layers. The film is deposited onto layers which are then assembled into the device.

WO 2022/013317 A1 describes carbon-based coating on adjacent hydrogen fuel cell bipolar plates, but the plates are separated from each other by the membrane electrode assembly or are assembled with intervening gaskets.

It remains a problem to seal electrical devices once assembled.

An object of the present invention is to provide alternative and preferably improved sealing of electrical devices such that they do not suffer from the problems noted above. An object of specific embodiments is to provide sealed electrical devices, wherein the sealing is cost-effective and provides suitable protection of electrical devices against environmental deterioration. It is particularly preferred that the sealing will additionally be non-selective and scalable in order to have wide applications for coating electrical devices.

Summary of the Invention

Accordingly, the present invention provides an electrical apparatus, comprising: at least first and second components, and an interface between the first and second components, wherein the apparatus further comprises:

(a) a coating of ta-C at the interface to seal the interface against ingress and/or egress of fluids, or

(b) a gasket at the interface, wherein the gasket comprises a coating of ta-C to seal the interface against ingress and/or egress of fluids.

The invention also provides a method of making an electrical apparatus, the method comprising:

(i) providing a first and second component,

(ii) connecting the first and second components to each other, and optionally attaching the first and second components together, so there is an interface between the components,

(ii) (a) applying a layer comprising ta-C to the interface between the first and second components, or (b) providing a gasket at the interface, wherein the gasket comprises a coating of ta-C.

It is found that sealed electrical apparatuses of the invention, as shown in examples below, exhibit reduced ingress and/or egress of fluids.

Detailed Description of the Invention

An electrical apparatus of the invention hence comprises: at least first and second components, and an interface between the first and second components, wherein the apparatus further comprises:

(a) a coating of ta-C at the interface to seal the interface against ingress and/or egress of fluids, or (b) a gasket at the interface, wherein the gasket comprises a coating of ta-C to seal the interface against ingress and/or egress of fluids.

An electrical apparatus (also referred to as an electrical device) is an apparatus that has an input and/or output of electricity. For example, an electrical device may be a device that produces electricity, e.g. a generator, a battery, a fuel cell, a solar cell, etc.As described in an example below, the electrical apparatus can comprise front and back layers and a lumen between the layers, the lumen generally comprising an air gap as well as an internal component, e.g. solar cell; ingress of water and/or moisture into this gap is a problem addressed in the invention. In preferred embodiments, the electrical apparatus is a fuel cell. In alternative preferred embodiments, the electrical apparatus is a solar cell.

In alternative embodiments an electrical device may be powered by electricity, e.g. a motor, a lighting device, an electronics device (e.g. an integrated circuit chip or OLED).

In other preferred embodiments, the electrical apparatus is an integrated circuit chip.

In further embodiments, the electrical apparatus may have both an input and output of electricity, for example the device may be a transformer.

The electrical apparatus of the invention may be a multilayer apparatus or layered composite stack. In such embodiments, the electrical apparatus comprises two or more layers of material; the two or more layers may be the same or different material. The layers meet and/or abut or mate and at the resultant interface between the two there is sealing according to the invention.

In an alternative embodiment, the electrical apparatus of the invention may be comprised within a layered composite stack. An example of an electronics device comprised within a layered composite stack, is a multifunctional energy storage composite (MES) comprising a lithium-ion battery embedded in a carbon-fibre composite. In such an embodiment, the ta-C may be present at an interface on the MES device, which is subsequently embedded within a layered composite stack. In particularly preferred embodiments of the invention, the electrical apparatus is selected from the list comprising a solar cell, an integrated circuit chip and a fuel cell assembly. When the electrical apparatus is a solar cell, it is particularly preferred that the solar cell is a perovskite solar cell. When the electrical apparatus is an integrated circuit chip, it is particularly preferred that the chip comprises a semiconductor contained within packaging. When the electrical apparatus is a fuel cell assembly, the fuel cell assembly may comprise alternating bipolar plates and membrane electrode assemblies (MEAs) separated by gaskets.

The first and second components may be any two components of the electrical apparatus that have an interface. In some embodiments, one or both of the first and second components may be sensitive to fluids. For example, one or both of the first and second components may degrade at an accelerated rate on contact with fluids. In alternative embodiments, the first and second components may define an interior volume in which a fluid-vulnerable component may be contained. In such embodiments it is beneficial to prevent the ingress of fluids into the interior volume. In further alternative embodiments, the first and second components may define a volume in which a fluid is contained. In such embodiments it is beneficial to prevent the egress of the fluid out of the interior volume.

The electrical apparatus may be a multilayer apparatus. In such embodiments, the first and second components may be adjacent layers within the multilayer apparatus. In such embodiments it is beneficial to prevent the ingress of fluids between the layers, in order to reduce the likelihood of delamination of the layers of the apparatus.

The material of the first component and second component depends on the application of the electrical apparatus. As such, it is envisaged that the first and second components of the electrical apparatus may be selected from a wide range of materials. However, in preferred embodiments, the material of the first and second components individually comprises or is selected from metals, alloys, glass, ceramic, composites and polymers (e.g. rubber, plastic) and compounds of the aforementioned. When the first and/or second component is or comprises a metal, the metal may be a metal with good conductivity, for example copper, aluminium, titanium. In alternative embodiments when the first and/or second component is or comprises a metal, the metal may be a metal with relatively poorer conductivity, for example if one component is or comprises steel.

In some embodiments, the first component and second component are made of the same material. In a preferred such embodiment, the electrical apparatus may be a solar cell assembly. In such embodiments, the first and second components may be made of glass (for example photovoltaic glass, such as soda-lime silica (SLS) glass, or borosilicate glass) or polymer (for example epoxy, TPU, PET).

In an alternative preferred such embodiment (where the first component and second component are made of the same material), the electrical apparatus may be an integrated circuit. In such embodiments, the first and second components may be made of plastic, metal or ceramic. Preferably the first and second components may be made of ceramic. The first component may be a base or partial packaging around a semiconductor chip, and the second component may be a further partial packaging or lid over the semiconductor chip. Together, the first and second components may form integrated circuit packaging. Interfaces between components of the packaged integrated circuit can be sealed according to the invention.

In some embodiments, the first component and second component are made of different materials. In one such embodiment, the electrical apparatus is or comprises a composite stack. Edges of layers within the stack form interfaces that are sealed according to the invention.

In a preferred such embodiment (where the first component and second component are made of different materials), the electrical apparatus may be an integrated circuit. The first component may be packaging around a semiconductor chip and may be made of epoxy resin. The second component may be an electrically conducting lead, e.g. connecting the semiconductor to other elements of the integrated circuit. The electrically conducting lead may be made of metal, e.g. copper. The second component may alternatively be a packaging substrate on which one or more semiconductor chips and electrically conducting leads are mounted. Interfaces within the product, e.g. an interface between a lead and a substrate, or between epoxy resin packaging and a packaging substrate can be sealed according to the invention. In an alternative embodiment where the electrical apparatus is an integrated circuit, the first and second components may be elements of semiconductor chip packaging forming a hybrid packaging system that involves two or more separately manufactured parts in heterogeneous integration or forming an advanced chip packaging system. The interface may therefore be the point at which any two parts of the packaging system are connected. Such interfaces can be sealed according to the invention.

In an alternative preferred such embodiment (where the first component and second component are made of different materials), the electrical apparatus may be a fuel cell stack. In such embodiments, the first component may be bipolar plate and the second component may be a membrane electrode assembly (MEA). In an alternative embodiment where the electrical apparatus is a fuel cell stack, the first component may be a bipolar plate and the second component may be a current collector plate. Typically, a bipolar plate is made of metal or alloy, e.g. steel, titanium or aluminium, or alloys thereof (preferably steel). The outer surface of an MEA may be a gas diffusion layer, as is conventional in the art. Typically the outer layer of an MEA is made of plastic (e.g. polyamide). A current collector plate may be a gold plated material, e.g. the outer surface of the current collector plate may be gold.

At the interface, the first and second components meet I abut, typically at meeting surfaces or mating surfaces; these surface may be connected. The first and second components may be directly connected (i.e. the first component is directly in contact with the second material, without any intervening material), or the first and second components may be indirectly connected via an adhesive, sealant and/or gasket (i.e. an adhesive, sealant and/or gasket is positioned between the first component and second component). Sealing using a ta-C coating according to the invention is achieved between the surfaces.

In an embodiment of the invention, the first and second components may be attached together at the interface, for example using an adhesive or sealant. Sealing according to the invention improves the seal at this interface. The coating of ta-C at the interface of the first and second components may extend at least partially onto a portion of the first component adjacent the interface. The coating may extend at least partially onto a portion of the second component adjacent the interface. Preferably, it extends onto both. In embodiments where adhesive, sealant or a gasket is present at the interface, the coating of ta-C may coat an outer edge of the adhesive, sealant or gasket, optionally in addition to extending at least partially onto a portion of the first and/or second component. In a preferred embodiment, a gasket is present at the interface between the first and second components, and a coating of ta-C is present at the interface and extends over an outer edge of the gasket and partially onto a portion of first and second components adjacent to the interface.

In embodiments of the invention, a hydrogen fuel cell gasket is coated with ta-C and used as a sealing gasket between bipolar plates. In testing designed to mimic approx. 10 years gasket life, ta-C coated gaskets have been found to show increased resistance to the acid environment encountered in fuel cells (pH around 2 during fuel cell operation) resulting in extended gasket lifetime.

Where an interface between first and second components is held together by adhesive, the present invention is believed applicable to a wide range of adhesives, without limitation. Both natural and synthetic adhesives can be used in the invention. Other examples of suitable adhesives include solvent-based adhesives and polymer dispersion adhesives, also known as emulsion adhesives, and pressure-sensitive adhesives. Commonly used synthetic adhesives used in the electrical and electronics industry and suitable for the invention are epoxy, acrylic, cyanoacrylate and silicone- based or -containing adhesives. Suitable adhesives may be polymers, and some suitable adhesives are cured adhesives or thermosetting adhesives that they change from a viscous liquid to a solid during “curing”.

In use of the invention, sealing of an electrical device is achieved or at least enhanced. Typically, to carry out the sealing the device is manufactured and then the sealing is carried out according to the invention on the manufactured product; the modified product is the sealed device and exhibits improved performance compared to the unsealed device. In embodiments of the invention, an electrical apparatus is provided comprising: at least first and second components, and an interface between the first and second components, wherein the apparatus is sealed by application of:

(b) a coating of ta-C onto a gasket at the interface seal the interface against ingress and/or egress of fluids.

It is known to apply sealants such as resins onto electrical devices during their manufacture. Further embodiments of the invention provide an electrical apparatus comprising at least first and second components, and an interface between the first and second components, wherein the apparatus or a part thereof is first sealed by encapsulation, and wherein the apparatus is further sealed by application of:

(a) a coating of ta-C onto the encapsulation to seal the encapsulation against ingress and/or egress of fluids.

Encapsulation is conventional in the electrical and electronics field, and may use thermosetting polymer or resin, especially epoxy resin.

When present, the sealant between the first and second components may be epoxy resin, ethylene-vinyl acetate, bismaleimide, ionomeric polymers (e.g. polyethylene ionomer, such as Surlyn®), polydimethyl siloxane, poly (methyl methacrylate) (PMMA), thermoplastic polyurethane (TPU), polyisobutylene and any mixture thereof. Fluoro polymers (e.g. PTEE), polyethylene terephthalate, poly (vinyl alcohol-co- ethylene)(EVOH), paraffin, organo siloxane, silicone and any mixture thereof can also be used as sealants. The preferred sealant is dependent on the application of the electrical device and the material of the first and second components. However, in some preferred embodiments, the sealant may be epoxy resin or bismaleimide.

The apparatus may comprise a gasket at the interface, wherein the gasket comprises a coating of ta-C. The gasket may improve the seal between the first and second components. The material of the gasket depends on the particular application of the gasket and the material of the first and second components. However, typically the gasket may be formed from metal, silicone, rubber, neoprene, a polymer (e.g. PTFE, polychlorotrifluoroethylene) or ceramic fibre. In preferred embodiments, the gasket may be formed from rubber, such as silicone rubber or EPDM rubber.

Hence, in embodiments of the invention, the gasket seals components of the device together and the invention provides an improved gasket, comprising a ta-C coating. In preferred embodiments where a ta-C coated gasket is present at the interface, the interface may additionally be coated with ta-C, e.g. there may be a ta-C coating across an edge of the first component, an edge of the ta-C coated gasket and across an edge of the second component.

The ta-C coating may be of various thicknesses, for example the thickness of the ta- C may depend on the application of the electrical apparatus. The layer comprising ta- C usually has a thickness of 0.2nm or greater, or 0.5nm or greater. As will be appreciated, above certain thicknesses little or no further improved sealing may be achieved. Generally, the thickness is up to 200nm, suitably up to 100nm. Typically, the thickness is from 1 nm to 50nm. In preferred embodiments the thickness is from 5nm to 10nm. Typically, the ta-C coating is applied directly to the surfaces of electrical devices (e.g. directly after cleaning the surface). As the coatings are relatively thin (e.g. 1 nm to 50nm), delamination is normally avoided. For coatings of increased thickness, say 50nm and above, it is optional to deposit a seed layer onto the assembly and then the ta-C layer. For example, in some packaging applications for electronic devices, a thin seed layer (e.g. of Ti, Cr, NiCr, Ni, Si) may be present between the substrate and ta-C coating, which may allow a thicker ta-C coating to be present without delamination. For some applications, thicker ta-C coatings (e.g. above 50nm) can help to ensure suitable sealing.

The ta-C coating usually has a density of 2.5g/cm³ or greater, preferably 3.0g/cm³ or greater.

The high surface atomic density of ta-C coating can prevent molecules from passing through the coating, thus the ta-C works effectively as a barrier layer. In use, the coating of ta-C seals the interface against ingress and/or egress of fluids. A fluid is a substance with no fixed shape and therefore encompasses both gases and liquids. The electrical apparatus of the invention therefore comprises a ta-C coating that seals the interface against gases and liquids. Preferred liquids against which the interface is sealed include water. Preferred gases against which the interface is sealed, include moisture, water vapour, oxygen, hydrogen and nitrogen.

Sealing of the interface against ingress and/or egress of fluids means reducing the flow of fluids across I through the interface. The flow of fluid through a ta-C coated interface may be reduced by at least 10%, for example at least 15%, preferably at least 20% compared to flow of the same fluid across a non-ta-C coated interface. Improved sealing results in longer shelf life of the device and/or reduced deterioration of internal components.

(i) providing a first and second component,

(iii) (a) applying a layer comprising ta-C to the interface between the first and second components, or (b) providing a gasket at the interface, wherein the gasket comprises a coating of ta-C.

Preferably the method comprises applying a layer comprising ta-C to the interface between the first and second components, and optionally also providing a gasket at the interface, wherein the gasket comprises a coating of ta-C. Suitably, the method comprises using the ta-C coated gasket to seal the interface and then applying a sealing layer of ta-C on top, covering at least a portion of the first component, the gasket and at least a portion of the second component.

Optional and preferred methods of the invention provide methods of making an electrical apparatus according to optional and preferred features of the apparatus. Prior to applying the layer comprising ta-C, the first and second components may be attached together. The first and second components may be attached together using adhesive or sealant as set out above.

In methods of the invention, the device / apparatus may be manufactured and then the sealing is carried out on the manufactured product.

In embodiments of the invention, a sealing method comprises making an electrical apparatus, said apparatus comprising at least first and second components and an interface between the first and second components, wherein the method further comprises applying a coating of ta-C at the interface to seal the interface against ingress and/or egress of fluids.

In further embodiments of the invention, a sealing method comprises making an electrical apparatus comprising at least first and second components and an interface between the first and second components, sealing the apparatus or a part thereof by encapsulation, and further sealing the apparatus by application of a coating of ta-C onto the encapsulation to seal the encapsulation against ingress and/or egress of fluids.

Sealing methods of the invention can provide an additional protective coating applied on top of polymer encapsulation to safeguard valuable components.

Sealing methods of the invention can include applying ta-C onto one or more exposed wires and/or onto exposed circuitry. An advantage, for example, is that this prevents water and/or oxygen from coming into contact with exposed wires - i.e. the wires that remain exposed but are now coated. When applied over exposed circuitry, the invention can have the benefit of allowing for direct observation during testing. Moreover, the coating can prove valuable when thermal imaging of hot spots on chips directly exposed to infrared equipment is required while maintaining packages under extreme conditions. The ta-C-coated electronic components can include microchips, sensors, MEMS devices, and more. The ta-C coating forms a protective barrier, preventing moisture and contaminants from reaching the sensitive electronic elements.

In a specific embodiment of the invention, described below in more detail, an IC chip is sealed with an outer layer of ta-C. In a specific embodiment of a method of the invention an IC chip is manufactured and then an outer layer of ta-C is applied to seal it.

In a further specific embodiment of the invention, described below in more detail, a solar cell is sealed with an outer layer of ta-C. In a specific embodiment of a method of the invention a solar cell is manufactured and then an outer layer of ta-C is applied to seal it.

Amorphous carbon is a free, reactive form of carbon which does not have a crystalline form. Various forms of amorphous carbon films exist and these are usually categorised by the hydrogen content of the film and the sp²:sp³ ratio of the carbon atoms in the film.

In an example of the literature in this field, amorphous carbon films are categorised into 7 categories (see table below taken from “Name Index of Carbon Coatings” from Fraunhofer Institut Schich- und Oberflachentechnik):

Tetrahedral hydrogen-free amorphous carbon (ta-C) is characterised in that it contains little or no hydrogen (less than 5%mol, typically less than 2%mol) and a high content of sp³ hybridised carbon atoms (typically greater than 80% of the carbon atoms being in the sp³ state). Ta-C sp² and sp³ levels are suitably measured by XPS (see e.g. https://doi.Org/10.1016/j.diamond.2003.11.077). Ta-C density is suitably measured using SIMS or RBS (see e.g. https://doi.Org/10.1016/S0257-8972(02)00247-5).

Whilst the term “diamond-like carbon” (DLC) is sometimes used to refer to all forms of amorphous carbon materials, the term as used herein refers to amorphous carbon materials other than ta-C. Common methods of DLC manufacture use hydrocarbons (such as acetylene), hence introducing hydrogen into the films (in contrast to ta-C films in which the raw material is typically hydrogen free high purity graphite).

The ta-C coating may be deposited using known technology, e.g. physical vapor deposition, of which one known technique is cathodic vapor arc deposition methods. In this method, an electric arc is used to vaporize material from a cathode target. Consequently, the resulting vaporized material condenses on a substrate to form a thin film of coating. Cathode arc deposition of tetrahedral amorphous carbon, metallic, dielectric and other such coatings is known in the art and offers the potential for deposition of thin films of high quality.

Ta-C is a dense amorphous material described as composed of disordered sp³, interlinked by strong bonds, similar to those that exist in disordered diamond (see Neuville S, “New application perspective for tetrahedral amorphous carbon coatings”, QScience Connect 2014:8, http://dx.doi.Org/10.5339/connect.2014.8). Due to its structural similarity with diamond, ta-C also is a very hard material with hardness values often greater than 30 GPa.

For use in the invention, the ta-C may have a hydrogen content less than 10%, typically 5% or less, preferably 2% or less (for example 1 % or less). The percentage content of hydrogen provided here refers to the molar percentage (rather than the percentage of hydrogen by mass). The ta-C is preferably not doped with other materials (either metals or non-metals). In preferred embodiments of the invention, as described in examples set out in detail below, the assemblies are coated with substantially hydrogen-free ta-C.

It is believed that ta-C coatings in general, used in the invention, achieve improved sealing. The sp³ carbon content is suitably 30% or higher, more suitably 40% or higher. It may range from 30% to 95%. Typically, the ta-C has an sp³ carbon content of 50% or higher. In preferred embodiments the ta-C has an sp³ content of 60% or higher, or 70% or higher, even more preferably above 80%.

The ta-C coating of the present invention is typically deposited by Filtered Cathodic Vacuum Arc (FCVA) and/or by sputtering, and machines and processes for both sputter and FCVA deposition of ta-C are conventional and known in the art and not features of the present invention. As will be appreciated, these coatings are carbon coatings and are preferably substantially silicon-free and oxygen-free. A suitable method and apparatus are described in WO 2012/044258, disclosing an “X-bend” system. Another example of a suitable deposition method is described in WO 2009/151404. A further example of a suitable deposition method is described in WO 2020/187744 - in particular the use of an adhesion promoting layer is described in this application. The ta-C coating of the present invention is preferably deposited by FCVA. As appreciated by the skilled person, FCVA apparatus produce a coating beam comprising positively charged, C⁺ ions for depositing ta-C coatings. For thin ta-C coatings, particulate defects may be of concern. FCVA deposition substantially removes macroparticles from the plasma beam and consequently can reduce of the quantity of macroparticles in the coatings. The “X bend” FCVA system may be particularly preferred in some cases because it can remove more macroparticles from the carbon plasma beam compared to conventional FCVA deposition.

Examples

The present invention is now described in more specific detail with reference to the accompanying drawings in which:

Fig. 1 shows a schematic view of a coated light emitting diode assembly;

Fig. 2 shows a schematic cross-section of a coated leaded integrated circuit package; Fig. 3 shows a schematic cross-section of four perovskite solar cell devices, being (a) a control and (b) - (d) embodiments of the invention;

Fig. 4 shows a schematic cross-section of a coated bipolar plate and gasket for a hydrogen fuel cell;

Fig. 5 shows an image of three of the devices shown schematically in Fig. 3, namely the control, TAC-1 and TAC-2, after a 6900-hour stability test;

Fig. 6 shows normalized power conversion efficiency (PCE) across 6900 hours of three of the devices shown schematically in Fig. 3, namely the control, TAC- 1 and TAC-2;

Fig. 7 is a schematic diagram of an encapsulated, integrated circuit (“IC") chip comprising sealing layers of ta-C; and

Fig. 8 shows results of testing control IC chips and IC chips sealed according to the invention.

Referring to the figures, Fig.1 shows a schematic view of a light emitting diode (LED) device assembly with a ta-C barrier coating deposited by FCVA. The LED device assembly has a conductive substrate (e.g. a printed circuit board), connected to a battery, on which an LED chip is positioned. The LED chip is an electronic component which directly emits light, it is made up of a small panel mounted with one or more LEDs which create an intense light. The light emitted is brighter for chips with more LEDs, e.g. a triple LED chip is brighter than a single LED chip. Positioned at the interface between the LED chip and substrate is die attach material. The LED chip is connected to a controller/resistor via a conductive copper wire. The controller/resistor (e.g. a ballast resistor) functions to limit the current through the LED, to prevent burn out of the LED.

A ta-C coating is deposited across the upper surface of the finished device using FCVA. A coating of ta-C is present on the exposed upper surface of the substrate and across the interface between the substrate and the LED chip, covering the exposed areas of the outer and upper edges of the die attach material, which is made of epoxy. This ta-C coating is continuous across the exposed upper and outer surfaces of the LED chip. A coating of ta-C additionally covers the interface between the LED chip and wire connecting the LED chip to the controller/resistor. The ta-C coating has approximately uniform thickness across the coated areas of the device assembly. In this example, the ta-C coating is 5nm - 10nm thick (in general the ta-C coating can have a thickness of 5-100nm) and sp³ content is about 80%.

In use, electrical power from the battery flows through the wire to the resistor, and then to the LED chip, where it is converted directly into light energy by the LED(s), for efficient light generation with minimal energy wasted.

The ta-C coating prevents ingress of water and or oxygen to the LED chip. This is important because the ingress of moisture can cause electrical shorts which can in turn cause the electrical assembly to malfunction. Water ingress can also be the cause of fire and electrical shock hazards in such LED devices. The ta-C barrier coating shown in Fig. 1 additionally has heat dissipative functionality, this means that it encourages the transfer of heat from the electrical assembly to its surrounding environment, by conduction. This is important to ensure that the operating temperature is controlled and to prevent overheating of the electrical assembly. Overheating can cause the lifespan of the assembly to be significantly decreased.

Fig. 2 shows a schematic cross-section of a leaded integrated circuit (IC) package with a ta-C barrier coating deposited by FCVA across the upper and outer surfaces of the ceramic packaging structure after its manufacture. The integrated circuit package has two conductive copper leads, one connected to the upstream end of a semiconducting electronic-grade silicon die and the other connected to a downstream end of the die. Both leads are additionally attached via conventional metallic alloy solder to a printed circuit board (PCB). The die is mounted on a die attach material, which is made of epoxy. The die and die attach material are encapsulated by a ceramic packaging structure. The ceramic packaging structure has a lower portion and upper (or lid) portion. The packaging protects the circuit material from corrosion and damage by environmental influences, however the packaging is non-hermetic and is therefore permeable to moisture and oxygen.

After manufacture of the IC package, the ta-C coating is applied to the packaging, like the one shown in Fig. 2, to improve the sealing of the packaging and to reduce ingress of water and oxygen to the die. The coating is thus applied directly onto the packaging and exposed circuitry. Reducing and/or preventing the ingress of moisture and oxygen reduces the likelihood of an electrical short in the circuit and further reduces environmental degradation of the components. The ta-C also protects the features of the microelectronic package, such as the wire bonds and die attach (DA) materials, from harsh environments, e.g. a high temperature harsh environment (HTHE).

In Fig. 2 the ta-C has been applied across the upper surface and side surfaces of the packaging structure, including at the interface between the upper and lower portions of the ceramic packaging. The coating is additionally present at the interface between the packaging and the copper leads, where a small amount of the coating will inevitably also be present on end of the leads closest to the packaging. The ta-C coating is of approximately uniform thickness across the coated areas of the packaging structure. In this example, the ta-C coating is 5nm - 10nm thick; in general the coating can also be thicker, for example the coating may be as thick as 50-1 OOnm.

Integrated circuits are able to function in many different ways, e.g. as an amplifier, oscillator, timer, microcontroller or microprocessor. In many of these applications, the integrated circuit may be buried inside other larger devices, which may make it challenging to remove and replace integrated circuits within such larger devices. It is therefore important that such integrated circuits have a sufficient lifetime to avoid this unnecessary inconvenience. Ta-C coatings can improve the lifetime of packaged integrated circuits.

Fig. 3 shows a schematic cross-section of four perovskite solar cell device stacks, namely (a) a control device, (b) “TAC-1”, (c) “TAC-2” and (d) “TAC-3”. The control is a conventional perovskite solar cell, encapsulated using lime-soda-silica (SLS) glass and sealed using epoxy sealant. “TAC-1” was encapsulated using normal SLS glass and then a layer of ta-C (sp³ content approx. 80%) was coated on the edges after sealing using epoxy. The ta-C coating is present across the interfaces between the back and front glass layers, passing across an edge of the front layer, the outer edge of the epoxy sealant, and an edge of the back layer on either side of the solar cell device. “TAC-2” was encapsulated using ta-C coated SLS glass for the back layer and normal SLS glass for the front layer and a layer of ta-C was coated on the edges after sealing using epoxy. The ta-C coating is therefore present along all the exposed surfaces of the glass back layer, across the interface between the front and back layers (i.e. across the epoxy sealant) and along the outer, i.e. side, edge of the front layer. “TAC-3” was encapsulated using ta-C coated SLS glass for both the front and back layers and a layer of ta-C was coated on the edges after sealing using epoxy. A continuous ta-C layer is therefore present on all of the exposed surfaces of the device assembly including across both interfaces between the front and back layers.

In additional embodiments, the ta-C may coat only the outer edge of the sealant, i.e. the interface between the front and back glass layers, or optionally the outer edge of the sealant and at least one portion of the back or front layer.

For the specific example of a perovskite solar cell shown in Fig.3 (d), “TAC-3”, the coating process was as follows. Firstly, the back and front glass layers were coated with a plasma beam, which contained positively charged carbon ions, substantially orthogonal to the glass plate. The ta-C coated glass was then cut in the required dimension and attached to the perovskite solar stack. Masking was then applied to the top and bottom glass surfaces (which had already been coated) while the side surfaces of the solar cell device were then coated with ta-C by FCVA deposition, without applying any substrate bias. The ta-C coating on the front surface was kept thin enough (e.g. approximately 5nm) to ensure that it was transparent. The ta-C coating on the edges was 20nm as for other tested devices.

Of course, the coating on the edges can be thicker because it does not need to be transparent, e.g. as thick as 10Onm or greater for enhanced function. However, thicker coatings increase cost and production times. For thicker ta-C coatings a seed layer is typically used to improve adhesion of the ta-C.

In use, solar cells like the one shown in Fig. 3 are exposed to harsh environments, leading to damage by abrasion, wind, UV and/or climate, especially rain. Perovskite solar cells, in particular, lack extrinsic stability towards environmental influences such as water and oxygen. This leads to the solar cells having short lifetimes, and therefore a lack of economic efficiency. The ta-C coating prevents ingress of water and oxygen, particularly at the interface between the glass layers, but also through pores in the sealant and glass layers. Therefore, the ta-C coating enables the solar cell device assembly to better withstand the harsh environments they are exposed to, which means they have a longer lifespan and, as a result, are more economically efficient.

Fig. 4 shows a schematic cross-section of a hydrogen fuel cell with a ta-C coating on the gaskets and across the interfaces between the gaskets and the bipolar plates.

The bipolar plates may be made of metal or graphite, preferably the bipolar plate is made of stainless steel, which may or may not have an additional surface coating. The bipolar plate shown on the top (i.e. adjacent the cathode gasket) of the fuel cell in Fig. 4 is the cathode and the bipolar plate shown on the bottom (i.e. adjacent the anode gasket) of the fuel cell in Fig. 4 is the anode. Hydrogen flow is on the anode side, while oxygen flow is on the cathode side, in each case flow of hydrogen I oxygen is between the relevant bipolar plate and the MEA. In between the two bipolar plates is a membrane electrode assembly (MEA). The MEA may be made up of seven layers, these being a middle layer of proton exchange membrane, a layer of catalyst on either side of the middle layer, a gas diffusion layer on either side of the catalyst layers and an outer layer of plastic at each edge to provide structural support. The layers of plastic may be polyamide layers. The MEA is adjacent each bipolar plate. The MEA and each of the bipolar plates are indirectly connected via gaskets present between the MEA and each bipolar plate. The gaskets are typically made of rubber, for example silicon rubber or ethylene propylene diene monomer (EPDM) rubber.

A ta-C coating is present over the surface of the gasket in contact with the MEA and additionally over the surface of each bipolar plate adjacent the MEA. In particular, the coating is present over the interface between the gaskets and the bipolar plates.

For the specific example of the hydrogen fuel cell shown in Fig. 4 the coating process was as follows. Firstly, the gaskets were attached to the top and bottom bipolar plates. A layer of ta-C (sp³ content approx. 80%) was then deposited to the upper surface (to which the gaskets were attached) of each bipolar plate, coating the upper and side surfaces of each gasket, the upper surface of the bipolar plate and the interface between the gaskets and the bipolar plate. The layer of ta-C was deposited by FCVA. In an alternative method of coating, the gaskets and optionally also the bipolar plates can be coated before construction of the fuel cell stack.

For the specific example of the hydrogen fuel cell shown in Fig. 4, in which the bipolar plates were coated together with the gaskets, the ta-C on the gaskets has the same thickness as the ta-C coating on the bipolar plates, which is a thickness of 400nm. In alternative embodiments the thickness of the ta-C coating on the gaskets may be different to the thickness of the ta-C coating on the bipolar plates. The ta-C coating on the gaskets is about 5nm - 10nm thick; in general, it may be as thick as a few hundred nanometres (e.g. the ta-C coating has a thickness of 5-100nm).

Fig. 5 shows the results of testing the stability of three of these devices, namely the control, TAC-1 and TAC-2. It shows that the control device displays the maximum degradation after 6900 hours, while the ta-C coated devices, TAC-1 and TAC-2 are visually still intact.

Fig. 6 shows graphically the results of stability testing of the same three devices. Each data point on the graph corresponds to the mean PCE of a range of 3 to 6 devices. It shows that the control device displays the maximum degradation whereas after 6900 hours at 50% RH and 20°C the ta-C coated devices, TAC-1 and TAC-2, have not yet reached their Tso lifetime (with Tso referring to time taken for the PCE to decrease by 20% from the initial value) within the timeframe measured. Additionally, the devices display T95 lifetimes (time taken for PCE to decrease by 5%) 28 and 34 times longer than the control, respectively. The T95 lifetime of the control device was found to be 127 hours, whereas the T95 lifetime of TAC-1 and TAC-2 devices were 3614 and 4351 hours, respectively. Thus, the solar cells treated according to the invention demonstrated improved stability.

Fig. 7 schematically shows an IC package in which a semiconductor DIE is attached to a substrate and a ta-C coating (sp³ content approx. 80%) is applied onto the DIE post manufacture. A “glob top” encapsulation using resin is deposited onto the DIE and a further coating of ta-C is optionally applied (see details below) onto the resin. Thus, a layer of ta-C was applied across the entirety of the top metal and wires (marked as the 1^st under coat, though not shown) prior to encapsulation; this coating, including onto exposed die surface and wires and wire bonds, prevents water and/or oxygen coming into contact with exposed components - see results and discussion below. An additional layer of ta-C was deposited after the completion of polymer encapsulation (again marked, as the 2^nd over coat, though not shown).

In more detail, the samples used were 12-pin dual in-line packages (DIP) with alumina packaging, featuring a gold coating on its upper surface.

A semiconductor die (referred to as DIE) was affixed to the DIP package’s surface by employing an epoxy-based die attachment material. Gold wire bonds, measuring 1 - mil (0.001 inch or 25pm) in diameter, were wedge-bonded onto the surface of the die, each connecting to distinct top metallization points. The schematic drawing illustrates the top metallization of the chip. The opposite ends of the gold wire were attached to the nearest metal fingers that surround the chip's housing on all four sides. The upper surface was not covered with encapsulation material and the top metal and wires were exposed.

Various configurations underwent testing, involving the application of a ta-C layer directly onto the chip/die and/or on top of the polymer encapsulation. The details of the experimental and control groups are shown in Table 1.

Set 1 : The chip was covered directly with a layer of ta-C, an epoxy glob top was added as encapsulation, and an additional layer of ta-C was deposited on the epoxy encapsulation.

Set 2: The chip was covered directly with a layer of ta-C and then covered with epoxy encapsulation.

Set 3: A layer of ta-C was directly applied after epoxy encapsulation.

Set 4: This served as a control. No ta-C layer was applied to either the exposed metal and wires or the epoxy encapsulation.

Table 1 : Encapsulation of electronic chips.

The encapsulated samples were placed in a humidity chamber under stringent environmental conditions, as stipulated by JEDEC Standard No. 22-A101 , at a combination of 85% relative humidity and 85°C, over a period of 750 hours.

To test the reliability of the packaged electronic chips, resistance of daisy chains was measured to check for resistance changes under JEDEC STD testing conditions.

Resistance changes are easily observable when moisture penetrates and comes into contact with wires or electrochemical reactions take place within the circuitry.

The effectiveness of ta-C in safeguarding the semiconductor die can be elucidated by the observed results in different experimental sets, shown in Fig. 8. Sets 1 and 2, where the die was comprehensively shielded by ta-C, exhibited a noteworthy outcome. These sets did not display any substantial increases in resistance even after an extended exposure period of 750 hours under conditions that replicate 85% relative humidity (RH) and 85°C, as per JEDEC Standard No. 22-A101. This observation underscores the protective prowess of ta-C in maintaining the electrical integrity and reliability of the semiconductor components it envelops. In contrast, Set 3, where ta-C coverage was confined to the exterior of the epoxy encapsulant, and Set 4, which entirely lacked ta-C protection, exhibited a divergent outcome. In these cases, there was a noticeable and rapid surge in resistance observed after surpassing the 250-hour mark. This substantial spike in resistance underscores the susceptibility of semiconductor components when not adequately shielded by ta-C. It underscores the critical importance of comprehensive ta-C coverage in mitigating the detrimental effects of extended exposure to challenging environmental conditions, including high humidity and elevated temperatures, on sem iconductor devices.

The invention thus provides for sealed electrical apparatuses coated with ta-C, and methods and apparatus therefor.

Claims

1 . An electrical apparatus, comprising: at least first and second components, and an interface between the first and second components, wherein the apparatus further comprises:

2. An electrical apparatus according to claim 1 , wherein the coating of ta-C has an sp³ content of 50% or higher.

3. An electrical apparatus according to claim 1 or 2, wherein the apparatus comprises (a) a coating of ta-C at the interface to seal the interface against ingress and/or egress of fluids.

4. An electrical apparatus according to claim 3, wherein the coating extends at least partially onto a portion of the first and/or second component adjacent the interface.

5. An electrical apparatus according to any preceding claim, wherein the first and second components are adjacent layers within a multilayer apparatus and the adjacent layers are sealed at their interface by sealant and/or adhesive and/or a gasket.

6. An electrical apparatus according to claim 5, wherein the ta-C coating covers (i) a portion of the first component adjacent the interface, (ii) a portion of the second component adjacent the interface and (iii) the sealant and/or adhesive and/or a gasket.

7. An electrical apparatus according to any preceding claim, wherein the electrical apparatus comprises a multilayer structure and the first and second components are adjacent layers of the multilayer structure.

8. An electrical apparatus according to claim 7, wherein the coating of ta-C is for reduction of delamination of the adjacent layers due to ingress of fluids, e.g. water and/or oxygen and/or hydrogen between the adjacent layers.

9. An electrical apparatus according to any preceding claim, wherein the first and second components are adjacent layers within a multilayer apparatus and the adjacent layers are made of the same material.

10. An electrical apparatus according to any preceding claim, wherein the electrical apparatus is a perovskite solar cell assembly.

11. An electrical apparatus according to claims 1 to 9, wherein the electrical apparatus is a fuel cell stack.

12. An electrical apparatus according to claims 1 to 9, wherein the electrical apparatus is an integrated circuit.

13. An electrical apparatus according to any preceding claim, wherein the electrical apparatus is an encapsulated electrical apparatus having a sealed interior and wherein the coating of ta-C at the interface seals the interface against ingress of water and/or oxygen into the sealed interior.

14. An electrical apparatus according to any preceding claim, wherein the coating of ta-C has a density of 2.5g/cm³ or greater and a thickness of 1 -50nm.

15. An electrical apparatus according to any preceding claim, wherein the coating of ta-C is substantially silicon-free and oxygen-free.

16. A method of making an electrical apparatus according to any preceding claim, the method comprising:

(i) providing a first and second component,

(ii) connecting the first and second components to each other, and optionally attaching the first and second components together, so there is an interface between the components, (iii) (a) applying a layer comprising ta-C to the interface between the first and second components, or (b) providing a gasket at the interface, wherein the gasket comprises a coating of ta-C.

17. A method according to claim 16, wherein the coating of ta-C has an sp³ content of 50% or higher.

18. An electrical apparatus according to any preceding claim, wherein the coating of ta-C is substantially silicon-free and oxygen-free.

19. A method according to any of claims 16-18, wherein the coating of ta-C has a density of 2.5g/cm³ or greater and a thickness of 1 -50nm.

20. A method according to any of claims 16 to 19, for making an electrical apparatus according to any of claims 1 to 15.