Two-Component Gap Filler Composition

The present invention relates to a two-component gap filler composition, a method of applying a gap filler to an electronic component, and an electronic component

5 comprising a gap filler formed of the two-component gap filler composition.

Many electronic applications today consist of a large number of components that have different heights, meaning they are not planar. This leads to gaps and tolerances that must be compensated for as part of efficient thermal management. This is because these components generate heat during operation. In order to avoid overheating and thus damaging the components and reducing their operational life, the thermally conductive properties of paste-like gap fillers and solid gap filler pads are used in such applications today. Thanks to their soft and long-term elastic character, they compensate for height differences between components. This allows them to be connected together

15 to a single heat sink or to a cooling housing. Above all, they minimise the thermal resistance between the electronic components and the heat sink, thus protecting the entire system from overheating and rapid ageing. Thanks to their elasticity, they also reduce vibrations to which sensitive applications are exposed.

20 The exact composition of thermal conductive materials is matched to the thermal conductivity and thermal contact in the application. In addition, there are aspects to be considered such as electrical insulation properties and maximum operating temperatures in which they operate. The available space and the budget also play a role. Most products are based on silicone elastomers, which are filled with thermally conductive

25 fillers - often ceramic powders based on aluminium oxide, zinc oxide or boron nitride. Among silicones, there are polymers with a very low content of volatile siloxanes (Low Volatile LW), which can play a role in the protection of contacts and the property of not repelling paint (LABS I PWIS).

Liquid or paste gap fillers are available as either one-component (1 K) or two-component (2K) fillers. One-part materials are highly viscous thermally conductive pastes that remain permanently liquid and behave thixotropically form-in-place. They can be applied with autodispensing equipment or by hand. In the case of two-part gap fillers, the two components of the thermally conductive material are stored separately and, in the case

35 of large-volume applications in automated production lines, are only mixed in a mixing

Received at EPO via Web-Form on Apr 28, 2023 tube via a lifting and dosing unit immediately before application and dispensed onto the application. There, the material polymerises until it is cured. These dispensing systems are associated with investments. For small-volume applications, manual dispensing is preferred. These materials are suitable for compensating extreme tolerances and gaps in

5 non-planar structures. Pressure is not necessary and does not occur, thus avoiding stress on components. This allows precise positioning (form-in-place) as well as placed curing (cure-in-place).

US2020270499 relates to a multicomponent-curable thermally-conductive silicone gel composition, thermally-conductive member and heat dissipation structure. US5021494 relates to a thermal conductive silicone composition. CN113897066A relates to a high thermally conductive double-component-derived thermal gel. WO 2021/128273 A1 relates to a two-part silicone composition and sealant and assembly made therefrom. CN 114395368 A relates to a two-component modified thermosetting silica gel and a

15 preparation method thereof. CN 114196209 A relates to an addition-curable two- component high-stability heat-conducting organic silicon composition and a preparation method thereof. CN 114181656 A relates to a bonding and sealing silicone material for a two-component low-viscosity photovoltaic module and a preparation method of a bonding and sealing silicone material. CN 113736266 A relates to a two-component

20 heat-conducting gel as well as a preparation method and application thereof. CN 113429930 A relates to an addition type two-component organic silicon pouring sealant and a preparation method thereof. CN 109337644 A relates to an addition type moulding room-temperature bonding two-component pouring sealant and a preparation method thereof. CN 108753246 A relates to a high thermal conductivity two-component pouring

25 sealant. CN 107964245 A relates to a dispensing gel heat conduction pad and a preparation method thereof. CN 107325782 A relates to a two-component pouring sealant and a preparation method thereof.

The problem with many conventional two-component gap filler compositions is that as the content of the thermally conductive filler increases, the viscosity may increase to the point where application to an electronic device is hindered, meaning that gaps may remain. In addition, the bond strength may be low and/or the bond strengthening time may be long. This may reduce device lifetime and/or increase the complexity of the manufacturing process.

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Received at EPO via Web-Form on Apr 28, 2023 The present invention seeks to tackle at least some of the problems associated with the prior art, or at least to provide a commercially acceptable alternative solution thereto.

In a first aspect, the present invention provides a two-component gap filler composition

5 comprising: a first component comprising a first polysiloxane and a first aluminium oxide powder; and a second component comprising a second polysiloxane and a second aluminium oxide powder.

Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

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The inventors have surprisingly found that in comparison to conventional two-component gap filler compositions, the composition of the present invention may exhibit a lower viscosity for the same thermal conductivity. This may result in easier and faster application.

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Advantageously, when used as an adhesive, the composition may exhibit improved bond strength. This may increase the reliability of a device containing a gap filler formed using the composition.

25 Furthermore, in comparison to conventional two-component gap filler compositions, the composition of the present application may develop bond strength more quickly. This may be advantageous during a production process using the composition.

The term “gap filler composition” as used herein may encompass a thermally conductive adhesive composition for filling a gap in an electronic device between an electronic component and a housing or heat sink.

The term “polysiloxane” as used herein may encompass a polymer made up of siloxane (-R2Si-O-SiR2-, where R = organic group). Polysiloxanes are sometimes

35 referred to as “silicones”.

Received at EPO via Web-Form on Apr 28, 2023 The first component and second component are typically different. The first polysiloxane and second polysiloxane may be the same or different, but are typically different. The first aluminium oxide powder and second aluminium oxide powder may be the same or

5 different.

The first polysiloxane and/or second polysiloxane may each comprise a single polysiloxane or multiple polysiloxanes.

The composition typically exhibits a high electrical resistivity. For example, the composition, when cured, may exhibit a volume resistivity of greater than or equal to 1 x 10 ¹³ Q cm, preferably greater than or equal to 1 x 10 ¹⁴ O cm, even more preferably greater than or equal to 1 x 10 ¹⁵ Q cm.

15 When cured, the composition typically exhibits a low thermal expansion coefficient, preferably less than or equal to 1 x 10' ³ m/mk, more preferably less than or equal to 1 x 10' ⁴ m/mk.

The first component and/or second component may be in the form of a paste of gel.

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The first aluminium oxide powder and/or the second aluminium oxide powder preferably has a multi-modal particle size distribution (e.g. a bi-modal, tri-modal or quad-modal), preferably a tri-modal or quad-modal particle size distribution. By “particle size”, it is meant the longest dimension of the particle. The particle size distribution, calculated on a

25 volume basis, may be determined by, for example, laser diffraction. Such particle size distributions may be particularly effective at providing a lower viscosity for the same thermal conductivity.

The particles of the first aluminium oxide powder and the second aluminium oxide powder may take the form of, for example, spheres, rods and/or plates. The first aluminium oxide powder and/or the second aluminium oxide powder preferably comprises substantially spherical particles, e.g. having an aspect ratio of less than 2 and substantially non-spherical particles, e.g. having an aspect ratio of two or more. By “aspect ratio” it is meant the ratio of the longest dimension to the shortest dimension of

35 the particle. For a completely spherical particle, the aspect ratio will be one. Such

Received at EPO via Web-Form on Apr 28, 2023 particles may be particularly effective at providing a lower viscosity for the same thermal conductivity. The substantially non-spherical particles make take the form of, for example, rods or plates.

5 The substantially spherical particles preferably have an aspect ratio of less than 1.5, more preferably less than 1.2, even more preferably about 1 ; and/or the substantially non-spherical particles preferably have an aspect ratio of three or more, more preferably four or more.

The substantially spherical particles preferably have a ratio of the maximum Feret diameter to the minimum Feret diameter of less than 1 .5, preferably less than 1 .2, more preferably about 1 ; and/or the substantially non-spherical particles have a ratio of the maximum Feret diameter to the minimum Feret diameter of 3 or more, preferably 4 or more. The maximum and minimum Feret diameters may be determined using, for

15 example, SEM. Such particles may be particularly effective at providing a lower viscosity for the same thermal conductivity.

The first aluminium oxide powder preferably comprises from 1 to 15 wt.% substantially spherical particles based on the total weight of the first aluminium oxide powder, more

20 preferably from 2 to 10 wt.%; and/or the second aluminium oxide powder preferably comprises from 1 to 15 wt.% substantially spherical particles based on the total weight of the second aluminium oxide powder, more preferably from 2 to 10 wt.%.

Preferably at least some of the particles in the first aluminium oxide powder and/or the

25 second aluminium oxide powder are surface-treated with a surface treatment agent I silane coupling agent. The surface treatment agent preferably comprises an alkylalkoxysilane, and preferably has the general formula R ¹ 4- _x Si(OR ² ) _x , where R ¹ is an alkyl group having from 1 to 20 carbon atoms, R ² is an alkyl group having from 1 to 4 carbon atoms and x is an integer between 1 and 3. The alkylalkoxysilane preferably comprises hexadecyltrimethoxysilane. The presence of such species may reduce the viscosity of the composition.

The first component preferably comprises from 85 to 99 wt.% of the first aluminium oxide powder, more preferably from 90 to 96 wt.% of the first aluminium oxide powder, based

35 on the total weight of the first component; and/or the second component comprises from

Received at EPO via Web-Form on Apr 28, 2023 85 to 99 wt.% of the second aluminium oxide powder, more preferably from 90 to 96 wt.% of the second aluminium oxide powder, based on the total weight of the second component. Lower contents of aluminium oxide powders may reduce the thermal conductivity of the composition. Higher contents of aluminium oxide may result in an

5 unfavourably high viscosity.

The two-component gap filler composition preferably comprises from 40 to 60 wt.% of the first component and from 40 to 60 wt.% of the second component. Higher levels may result in an unfavourably high viscosity and/or an unfavourably low bond strength and/or an unfavourably long bond strength-forming time.

The first component and the second component are preferably stored separately. This may ensure that they do not cure during storage.

15 The first component and/or the second component preferably comprises a colorant. In this regard, The first component and the second component may be different colours. This may enable the first component to be a different colour to the second component. As a result, it is easier to control the relative amounts of the first component and second component in use.

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The first component and/or the second component preferably further comprises a catalyst. The catalyst preferably comprises one or both of palladium and platinum. The presence of such catalysts may serve to increase the curing rate of the composition. Preferably, the catalyst is present in only one of the first component and the second

25 component.

The first component and/or the second component preferably comprises a solvent. The solvent preferably comprises toluene. This may result in a more favourable viscosity, thereby enabling easier dispensing and more accurate placement.

The first component and/or the second component preferably further comprises a silane coupling agent. The silane coupling agent preferably comprises an alklypolysiloxane, more preferably octamethyltrisiloxane. The use of a silane coupling agent may reduce the viscosity of the composition for the same volume of aluminium oxide powder.

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Received at EPO via Web-Form on Apr 28, 2023 The first polysiloxane preferably comprises an alkenyl group-containing organopolysiloxane.

The second polysiloxane preferably comprises an organohydrogenpolysiloxane.

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The first component and/or the second component preferably further comprises a hydrosilylation reaction catalyst.

The two-component gap filler composition preferably has a thermal conductivity of at least 2 W/mK, preferably at least 3 W/mK, more preferably at least 4 W/mK, even more preferably least 5 W/mK. This may improve the performance of a device containing a gap filler formed using the composition.

The composition is preferably a room temperature vulcanizing composition.

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In a further aspect the present invention provides a two-component gap filler composition comprising: a first component comprising a first polysiloxane and a first thermally conductive filler; and

20 a second component comprising a second polysiloxane and a second thermally conductive filler.

The advantages and preferable features of the first aspect apply equally to this aspect.

25 The first thermally conductive filler and/or the second thermally conductive filler may be in the form of a powder or fibres, preferably a powder.

Preferably, the first thermally conductive filler and/or the second thermally conductive filler comprises one or more of metal oxides, metal hydroxides, metal nitrides, metal carbides, metal silicides and carbons, preferably metal oxide, metal nitride and carbon, more preferably aluminium oxide, boron nitride and zirconium oxide.

In a further aspect the present invention provides a gap filler comprising the two- component gap filler composition described herein in cured form.

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Received at EPO via Web-Form on Apr 28, 2023 In a further aspect, the present invention provides a kit for forming a gap filler, the kit comprising: a first component comprising a first polysiloxane and a first aluminium oxide powder; and

5 a second component comprising a second polysiloxane and a second aluminium oxide powder.

The advantages and preferable features of the first aspect apply equally to this aspect.

In a further aspect the present invention provides a method of applying a gap filler to an electronic component, the method comprising: providing an electronic component, providing the two-component gap filler composition as described herein, contacting the first component and the second component to provide a contacted

15 two-component gap filler composition, and applying the contacted two-component gap filler composition to the electronic component.

The advantages and preferable features of the first aspect apply equally to this aspect.

20

The electronic component preferably comprises a printed circuit board.

The electronic component preferably comprises a metal housing and applying the contacted two-component gap filler composition to the electronic component comprises

25 disposing the contacted two-component gap filler composition to the electronic component between the printed circuit board and the housing.

In a further aspect, the present invention provides a method of applying a gap filler to an electronic component, the method comprising: providing an electronic component, providing a first component comprising a first polysiloxane and a first aluminium oxide powder, providing a second component comprising a second polysiloxane and a second aluminium oxide powder,

35 contacting the first component and the second component, and

Received at EPO via Web-Form on Apr 28, 2023 applying contacted first component and second component to the electronic component.

The advantages and preferable features of the first aspect apply equally to this aspect.

5

The electronic component preferably comprises a printed circuit board.

The electronic component preferably comprises a metal housing and applying the contacted first component and second component to the electronic component comprises disposing the contacted first component and second component between the printed circuit board and the housing.

Preferably, the first component and second component are part of the two-component gap filler composition described herein.

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In a further aspect, the present invention provides an electronic component comprising a gap filler formed of the two-component gap filler composition described herein.

The advantages and preferable features of the first aspect apply equally to this aspect.

20

The electronic component preferably comprises a printed circuit board.

In a further aspect, the present invention provides an electronic component comprising a gap filler formed of the two-component gap filler composition described herein.

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The advantages and preferable features of the first aspect apply equally to this aspect.

The electronic component preferably comprises a printed circuit board.

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

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Received at EPO via Web-Form on Apr 28, 2023