Thermally conductive polymer

Abstract

A composition comprising a polymer comprising a repeat unit of formula (I) and at least one of a curable material comprising a plurality of crosslinkable groups and a curing agent capable of reacting with a crosslinkable material to form a crosslinked network, X1 and X2 are each independently selected from formulae (II) and (III): -(Ar1)m- Formula (II), -(Ar2)p-L-(Ar3)q- Formula (III, wherein Ar1, Ar2 and Ar3 in each occurrence is an arylene or heteroarylene group; m is at least 1; p is 0, 1, 2 or 3; q is 0, 1, 2 or 3, and L is selected from O, S, C=O, COO, CONR5, NR5, Si(R6)2 C(R7)2 and an optionally substituted chain of methylene (-CH2-) groups wherein one or more non-adjacent methylene groups may be replaced with O, S, C=O, COO, CONR5, NR5 or Si(R6)2 wherein R5 is H or a substituent; each R6 is independently a substituent; and each R7 is independently a substituent; one of Y1 and Y2 is CR1 wherein R1 is H or a substituent; and the other of Y1 and Y2 is N; and one of Y3 and Y4 is CR1; and the other of Y3 and Y4 is N.

Description

[0001] THERMALLY CONDUCTIVE POLYMER

[0002] BACKGROUND

[0003] Thermally conductive materials are used in a wide variety of applications including in underfill for flip-chips to reduce thermally induced stresses following application of a flip chip or as an interface between a surface of a heat generator and a surface of a heat dissipator.

[0004] Jinhong Yu et al, "Polymer / boron nitride nanosheet composite with high thermal conductivity and sufficient dielectric strength", Polymers Advanced Technologies, Volume 26, Issue 5 2015 pages 514-520 discloses epoxy composites incorporating boron nitride nanosheets.

[0005] US11326843 discloses a thermal interface sheet containing a base material and a filler material.

[0006] US2015 / 318227 discloses a composition of a polyimide, an epoxy resin and a heat-conductive filler.

[0007] WO 2022 / 136584 discloses thermally conductive polymers formed by reaction of a dialdehyde and a diamine.

[0008] Zhiyong Li et al, "Sustainable paeonol-derived polyimine-epoxy as a substitute for DGEBA thermoset", Reactive and Functional Polymers 194 (2024) 105804 discloses a bio-based mono-aromatic epoxy resin, l-(2,4-bis (oxiran-2-ylmethoxy)phenyl)-ethan-l-one (BPEO) derived from paeonol to provide a solvent-free, environmentally friendly curing technique. Maoping Lyu et al, "Vanillin-based liquid crystalline polyimine thermosets and their composites for recyclable thermal management application", Composites Part B 250 (2023) 110462 discloses trifunctional aldehyde monomer prepared from vanillin which is cured with two kinds of diamine to form a polyimine network.

[0009] SUMMARY

[0010] The present disclosure provides a composition comprising a polymer comprising a repeat unit of formula (I) and at least one of a curable material comprising a plurality of crosslinkable groups and a curing agent capable of reacting with a crosslinkable material to form a crosslinked network:

[0011]

[0012] wherein:

[0013] X1and X2are each independently selected from formulae (II) and (III):

[0014] -(Ar^m Formula (II)

[0015] -(Ar2)P-L-(Ar3)qFormula (III)

[0016] wherein Ar1, Ar2and Ar3in each occurrence is an arylene or heteroarylene group; m is at least 1; p is 0, 1, 2 or 3; q is 0, 1, 2 or 3, and L is selected from O, S, C=O, COO, CONR5, NR5, Si(R5)2 C(R7)2and an optionally substituted chain of methylene (-CH2-) groups wherein one or more non-adjacent methylene groups may be replaced with O, S, C=O, COO, CONR5, NR5or Si(R5)2wherein R5is H or a substituent; each R5is independently a substituent; and each R7is independently a substituent;

[0017] one of Y1and Y2is CR1wherein R1is H or a substituent; and the other of Y1and Y2is N; and

[0018] one of Y3and Y4is CR1; and the other of Y3and Y4is N.

[0019] Optionally, the curable material comprises a plurality of crosslinkable groups selected from:

[0020] an acyclic unit of formula -CR10=CH2wherein R10is H or a substituent;

[0021] a cyclic alkene unit;

[0022] an optionally substituted epoxide unit;

[0023] an optionally substituted oxetane unit; and

[0024] an optionally substituted benzocyclobutene unit.

[0025] Optionally, the curable material comprises a plurality of optionally substituted epoxide Optionally, the composition further comprises a curing agent comprising a plurality of amine groups.

[0026] Optionally, the curing agent is a branched polyethyleneimine.

[0027] Optionally, the curable material is a polymerisable monomer.

[0028] Optionally, the curable material is a curable polymer.

[0029] Optionally, the curable polymer comprises a repeat unit comprising an alkylene-oxy group, optionally an ethyleneoxy repeat unit.

[0030] Optionally, Y1and Y4are both the same one of CR1and N; and Y2and Y3are both the same and are the other one of CR1and N.

[0031] Optionally, Ar1, Ar2and Ar3are each, independently in each occurrence, selected from a 6-12 membered arylene or an optionally fused 5- or 6-membered heteroarylene.

[0032] Optionally, Ar1, Ar2and Ar3independently in each occurrence is an unsubstituted or substituted para-phenylene.

[0033] Optionally, p and q are each 1.

[0034] Optionally, the composition consists of the polymer and the curable material.

[0035] Optionally, the curable material : polymer ratio is in the range of 1:99 wt % to 99:1 wt%. Optionally, the composition further comprises a thermally conductive particulate material. According to these embodiments, optionally the curable material : polymer ratio is in the range of 1:99 wt % to 99:1 wt%.

[0036] Optionally, the thermally conductive particulate material is 5-80 wt % of the composition. The present disclosure provides a formulation comprising the composition as described herein and one or more solvents wherein the curable material and the polymer are dissolved in the one or more solvents.

[0037] The present disclosure provides a method of forming a cured structure comprising curing a composition as described herein wherein the composition comprises the curable material and the polymer. Optionally, the composition further comprises the curing agent.

[0038] The present disclosure provides a film comprising a composition as described herein. The present disclosure provides a cured film comprising a composition as described herein in which the curable material has been cured.

[0039] The present disclosure provides a method of forming a film as described herein wherein the film is formed by a thermal processing method. Optionally, the thermal processing method is selected from extrusion, injection moulding, thermocompressive bonding and hot press or melt press moulding.

[0040] The present disclosure provides an electronic device comprising a film as described herein disposed on a surface of a functional layer of the electronic device. Optionally, the film is disposed in a region between the surface of the functional layer and a first surface of a first chip electrically connected to the functional layer. Optionally, the functional layer is a printed circuit board; an interposer; or a second chip.

[0041] Optionally, the electronic device comprises a plurality of films as described herein.

[0042] Optionally, the electronic device comprises a 3D chip stack.

[0043] The present disclosure provides apparatus comprising a heat-generating device, a heat transfer device configured to transfer heat away from the heat-generating device and a film as described herein disposed between the heat-generating device and the heat transfer device.

[0044] The present disclosure provides a heat sink comprising a first surface having fins extending therefrom and an opposing second surface having a film as described herein disposed thereon.

[0045] DESCRIPTION OF DRAWINGS

[0046] Figure 1 schematically illustrates a 3D chip stack according to an embodiment of the present disclosure;

[0047] Figure 2 schematically illustrates a substrate for measurement of thermal conductivity of a film; and

[0048] Figures 3A and 3B schematically illustrate apparatus for measurement of thermal conductivity including the substrate of Figure 2.

[0049] The drawings are not drawn to scale and have various viewpoints and perspectives. The drawings are some implementations and examples. Additionally, some components and / or operations may be separated into different blocks or combined into a single block for the purposes of discussion of some of the embodiments of the disclosed technology. Moreover, while the technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the technology to the particular implementations described. On the contrary, the technology is intended to cover all modifications, equivalents, and alternatives falling within the scope of the technology as defined by the appended claims.

[0050] DETAILED DESCRIPTION

[0051] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word : any of the items in the list, all of the items in the list, and any combination of the items in the list. References to a layer "over" another layer when used in this application means that the layers may be in direct contact or one or more intervening layers may be present. References to a layer "on" another layer when used in this application means that the layers are in direct contact. References to a chemical element include isotopes of that element.

[0052] The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements. These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

[0053] To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms.

[0054] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

[0055] Polymer comprising a repeating structure of formula (11

[0056] Optionally, thermal conductivity of polymers comprising a repeating structure of formula (I) as described herein is at least 0.15 Wm K_1, optionally at least 0.4, 0.5, 0.6 or 0.7 Wm-1K-1. Thermal conductivity of a polymer may be measured as described herein using a neat film of the polymer.

[0057] The polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography of the polymers comprising a repeating structure of formula (I) described herein may be in the range of about lxlO3to 1x10s, and preferably lxlO4to 5xl05. The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers comprising a repeating structure of formula (I) described herein may be lxlO3to 1x10®, and preferably lxlO4to lxlO7.

[0058] Polymers comprising a repeating structure of formula (I) as described herein are preferably at least partially crystalline.

[0059] Polymers comprising a repeating structure of formula (I) as described herein may undergo pi-pi stacking when deposited as a film.

[0060] Preferably, polymers comprising a repeating structure of formula (I) are linear polymers. The polymer comprising a repeating structure of formula (I) may or may not be substituted with a crosslinkable group capable of reacting with the curable material. Preferably, the polymer comprising a repeating structure of formula (I) is not substituted with a crosslinkable group.

[0061] The polymer comprising a repeating structure of formula (I) may have end-groups capable of reacting with a curing agent, for example aldehyde end-groups capable of reacting with amine groups of a curing agent. In these embodiments, it will be understood that both the polymer comprising the repeating structure of formula (I) and the curable material may react with the curing agent.

[0062] L groups

[0063] L is selected from O, S, C=O, COO, CONR5, NR5, Si(R5)2 C(R7)2 and an optionally substituted chain of methylene (-CH2-) groups wherein one or more non-adjacent methylene groups may be replaced with O, S, C=O, COO, CONR5, NR5or Si(R5)2 wherein R5is H or a substituent; each R5is independently a substituent; and each R7is independently a substituent.

[0064] R5is preferably H or a C1-20 hydrocarbyl group.

[0065] R5is preferably a C1-20 hydrocarbyl group.

[0066] R7is preferably H, F or an optionally fluorinated C1-20 hydrocarbyl group.

[0067] Unless otherwise stated, a C1-20 hydrocarbyl group as described anywhere herein is preferably a C1-20 alkyl or phenyl which is unsubstituted or substituted with one or more Ci-14 alkyl groups, optionally one or more C1-12 alkyl groups.

[0068] One or more H atoms of the methylene groups of L may be replaced with one or more substituents. Optionally, one or more H atoms are replaced with F, C1-6 alkyl or C1-6 fluoroalkyl.

[0069] Preferably, L is a chain of methylene groups in which one or more non-adjacent methylene groups are optionally replaced with O atoms. Exemplary groups L include, without limitation, -OCH2CH2O- and -OCH2O-.

[0070] Preferably, L contains no more than 4 atoms separating Ar2and Ar3, optionally no more than 3 or 2 atoms separating Ar2and Ar3.

[0071] X1and X2

[0072] Optionally, X1and X2are each independently a group of formula (II).

[0073] Preferably, at least one of X1and X2is a group of formula (III). More preferably, one of X1and X2is a group of formula (II) and the other of X1and X2is a group of formula (III). Y1- Y4

[0074] R1is preferably H or a C1-20 hydrocarbyl group, more preferably H or a C1-6 alkyl group, most preferably H.

[0075] Preferably, Y1and Y4are both the same one of CR1and N; and Y2and Y3are both the same and are the other one of CR1and N. Preferably, R1of each CR1is the same.

[0076] A^-Ar3

[0077] Preferably, Ar1, Ar2and Ar3are each, independently in each occurrence, selected from a 6-12 membered arylene or an optionally fused 5- or 6-membered heteroarylene, e.g., an unfused 5- or 6-membered heteroarylene or a benzene-fused 5- or 6-membered heteroarylene. Exemplary groups Ar1, Ar2and Ar3include, without limitation, paraphenylene, thiophene, furan, and benzobisoxazole, each of which may independently be unsubstituted or substituted with one or more substituents. Para-phenylene is preferred. m is preferably more than 1, preferably 2-5, more preferably 2 or 3.

[0078] p and q are preferably each independently 1 or 2, more preferably 1.

[0079] Each of Ar1, Ar2and Ar3is independently unsubstituted or substituted with one or more substituents R2.

[0080] Preferably, where present R2in each occurrence is independently selected from:

[0081] F;

[0082] CN;

[0083] NO2;

[0084] branched, linear or cyclic C1-40 alkyl, preferably C1-20 alkyl, wherein one or more non-adjacent C-atoms may be replaced with O, S, NR5, SiR52, C=O or COO; wherein R5in each occurrence is H or a substituent, preferably H or a C1-20 hydrocarbyl group and R5in each occurrence is independently a substituent, optionally a C1-20 hydrocarbyl group; or an aryl or heteroaryl group Ar5which is unsubstituted or substituted with one or more substituents, optionally phenyl which is unsubstituted or substituted with one or more substituents selected from F, CN, NO2 and branched, linear or cyclic C1-20 alkyl wherein one or more non-adjacent C-atoms may be replaced with O, S, NR5, SiR52, C=O or COO. Preferably, at least one substituent R2, optionally each substituent R2, is C1-20 alkyl, C1-20 alkoxy, a group of formula -(Ak1)y-(OCH2CH2)z-Ak2wherein Ak1is a C1-4 alkylene group; y is 0 or 1; z is 1-15; and Ak2is a C1-4 alkyl group. More preferably R2is a C1-12 alkyl or Ci-12 alkoxy.

[0085] Exemplary groups -(Ar^m- include, without limitation, groups of formulae (Via) and (VIb):

[0086]

[0087] wherein R2independently in each occurrence is a substituent and w in each occurrence is independently 0 or a positive integer.

[0088] A preferred group -(Ar^m- has formula (VIb-1):

[0089]

[0090] (VIb-1)

[0091] Ar2and Ar3are each preferably optionally substituted 1,4-phenylene, more preferably unsubstituted 1,4-phenylene.

[0092] The polymer may be formed by polymerisation of a first monomer and a second monomer wherein the first and second monomers react to form imine (-CR^N-) linkages between X1and X2. Suitable reactive groups for reaction to form imine linkages are aldehyde or ketone (-C(=O)R1) reactive groups, preferably aldehyde reactive groups, and amine (NH2) reactive groups.

[0093] Accordingly, polymerisation may be between a first monomer of formula Ml and a second monomer of formula M2:

[0094] RG1-X1-RG1Ml

[0095] RG2-X2-RG2M2 wherein each RG1is a first reactive group selected from C(=O)R1and NH2 and each RG2is a second reactive group which is the other of C(=O)R1and NH2.

[0096] Preferably, each RG1is C(=O)R1and each RG2is NH2.

[0097] It will be understood that polymerisation of dialdehyde monomer(s) and diamine monomer(s) gives a linear polymer.

[0098] The reaction between RG1and RG2may be catalysed by a Lewis acid. The Lewis acid may be a Bronsted-Lowry acid. Exemplary catalysts include, without limitation, sulfonic acids and salts thereof, for example p-toluene sulfonic acid; triflic acid; and salts thereof; and aromatic alcohols, more preferably benzene which is substituted with at least one hydroxyl group and, optionally, one or more further substituents for example one or more C1-6 alkyl groups.

[0099] An exemplary triflic acid salt is scandium triflate, Sc(Tf)s.

[0100] Exemplary aromatic alcohols are phenol which is unsubstituted or substituted with one more C1-6 alkyl groups, more preferably one or more methyl groups, for example m-cresoL The reaction may be catalysed by a C1-12 hydrocarbyl ester of salicylic acid, optionally ethyl salicylate.

[0101] The catalyst may be provided in an amount of 0.01-5 molar equivalents of the total number of moles of the monomers. The catalyst is suitably soluble in the solvent or solvent mixture in which the monomer or monomers are dissolved.

[0102] Optionally, the solvent or solvents used in polymerisation are selected from tetra hydro furan, 2-methyltetrahydrofuran, benzene or naphthalene optionally substituted with one or more substituents, optionally one or more substituents selected from C1-12 alkyl, C 1 12 alkoxy, F and Cl; ethers; esters; halogenated alkanes; ketones; sulfoxides; and mixtures thereof. Exemplary solvents include, without limitation, toluene, xylenes, 1,2,4-trimethylbenzene, mesitylene, tetrahydrofuran, 2-methyltetrahydrofuran, 1-methylnaphthalene, 1-chloronaphthalene, , anisole, N-methylpyrrolidone, 1,2-dimethoxybenzene, dimethylsulfoxide and l,3-dimethyl-2-imidazolidinone.

[0103] The polymerisation may be as described in WO 2022 / 136584, the contents of which are incorporated herein by reference.

[0104] Curable material The curable material is a material that is separate from and mixed with the polymer comprising the repeat unit of formula (I). The curable material may be a polymeric or non-polymeric material substituted with a plurality of crosslinkable groups.

[0105] A curable polymer may comprise a repeat unit substituted with one or more crosslinkable groups, and I or crosslinkable end-groups.

[0106] A preferred curable polymer comprises alkyleneoxy repeat units, more preferably ethyleneoxy repeat units. Preferably, the curable polymer comprising alkyleneoxy repeat units comprises crosslinkable end-groups.

[0107] The curable material may be a curable monomer comprising a core unit substituted with a plurality of crosslinkable groups. The core unit is preferably selected from optionally substituted C6-12 arylene groups, preferably benzene and optionally substituted C1-12 alkylene groups and combinations thereof. Where these groups are linked they may be directly linked to one another or may be linked through a linking group. Optional substituents of C1-12 alkylene are preferably F and C1-6 alkyl. Optional substituents of C6-12 arylene are F, Cl, Br, CN, NO2, and C1-6 alkyl wherein one or more H atoms may be replaced with F.

[0108] The core unit may be a group of formula (VII)

[0109]

[0110] wherein X is selected from optionally substituted C1-12 alkylene; -C(=C(R4)2)-; SO; and SO2 wherein R4in each occurrence is H or a substituent, preferably H, F or Cl. Optional substituents of a C1-4 alkylene group are preferably F; Cl; C1-6 alkyl; and phenyl. Two alkyl groups linked to the same C atom of a C1-4 alkylene group X may be linked to form a ring. Crosslinkable groups are preferably selected from groups of formula (IV):

[0111] -(Sp)y-(XL)z

[0112] (IV)

[0113] wherein Sp is a spacer group; y is 0 or 1; z is 1 if y is 0; and z is at least 1, preferably 1-4 if z is greater than 1, and XL is a crosslinkable unit.

[0114] Optionally, XL is selected from (i) an acyclic unit of formula -CR10=CH2 wherein R10is H or a substituent, preferably a Ci-6 alkyl group, for example vinyl, styryl acrylate or methacrylate; (ii) a cyclic alkene, preferably an optionally substituted norbornene, cyclopropene or cyclobutene;

[0115] (iii) an optionally substituted epoxide;

[0116] (iv) an optionally substituted oxetane; and

[0117] (v) an optionally substituted benzocyclobutene.

[0118] Sp is preferably selected from optionally substituted phenylene; and C1-20 alkylene wherein one or more H atoms of the C1-20 alkylene may be replaced with F and one or more non-adjacent C atoms may be replaced with O, S, NR5, Si(R5)2, CO, COO or CONR5wherein R5is H or a substituent as described above and each R5is independently a substituent, optionally a C1-20 hydrocarbyl group.

[0119] Optional substituents of a phenylene group Sp are F; CN; NO2; and C1-20 alkylene wherein one or more H atoms may be replaced with F and one or more non-adjacent C atoms may be replaced with O, S, NR5, Si(R5)2, CO, COO or CONR5.

[0120] Optional substituents of an epoxide or oxetane are preferably selected from C1-12 alkyl and C1-12 alkoxy.

[0121] The curable material may be capable of reacting with itself to form a crosslinked network. In this case, the composition may comprise a polymerisation initiator.

[0122] The curable material may be an oligomeric material comprising a plurality of linked core units. The curable material may be a mixture of oligomers, for example a mixture of compounds having 1-10 core units.

[0123] The curable material may be capable of reacting with a curing agent. In the case where XL is epoxide, the composition preferably further comprises a curing agent. A preferred curing agent is a material comprising a plurality of amine groups, more preferably a plurality of NH2 groups.

[0124] The curing agent may comprise a plurality of acid anhydride groups.

[0125] The curing agent may be polymeric or non-polymeric.

[0126] An exemplary polymeric curing agent is branched poly(ethyleneimine) (PEI).

[0127] An optionally substituted benzocyclobutene group XL may have formula (V):

[0128]

[0129] wherein R8in each occurrence is H or a substituent; z is 0, 1, 2 or 3, preferably 0; R9in each occurrence is a substituent; and * is a bond to Sp or, if y is 0, a direct bond to the polymer backbone.

[0130] Preferably, of two R8groups bound to the same carbon atom at least one R8is H. Optionally, each R8of formula (V) is H or only one R8of formula (V) is not H. Exemplary non-H groups R8are Ci-6 alkyl, Ci-6 alkoxy and a phenyl which is unsubstituted or substituted with one or more Ci-6 alkyl groups.

[0131] R9, if present, is preferably selected from F, Cl, NO2, CN, C1-6 alkyl and C1-6 alkoxy.

[0132] The weight ratio in the composition of the polymer comprising a repeating structure of formula (I) : curable material may be in the range of 99:1 - 1:99, optionally 90:10 -10:90.

[0133] Optionally, the curing agent does not comprise a plurality of amine groups. Optionally, the curing agent is not PEI.

[0134] The curing agent may be a cationic catalyst, for example (4-hydroxyphenyl)methyl(2-methylbenzyl)sulfonium hexafluoroantimonate.

[0135] The curing agent may be a catalyst which releases H+upon one or both of thermal and light treatment.

[0136] Further components

[0137] A composition as described herein may consist of the polymer comprising a repeating structure of formula (I) and the curable material or may comprise one or more further components. Exemplary further components include a curing agent, or hardener, capable of reacting with the curable material to form a crosslinked network; a polymerisation initiator in the case where the composition comprises a curable monomer or oligomer; an accelerator and inorganic thermally conductive particles, preferably boron nitride or aluminium oxide particles. The thermally conductive particles may be provided in an amount of 5-80 wt% of the total mass of the composition, optionally 10-50 wt%.

[0138] Inorganic thermally conductive particles such as boron nitride as described herein may be substituted with an organic group, optionally an aromatic group, for example an oligo-(hetero)arylene comprising 1-10 arylene or heteroarylene groups, or a poly-(hetero)arylene. An exemplary surface group is an oligophenylene, for example biphenyl or terphenyl. Surface groups of a thermally conductive particle are disclosed in WO2022 / 207695, the contents of which are incorporated herein by reference.

[0139] Film formation

[0140] Formation of a cured film may comprise formation of a precursor film comprising the polymer comprising the repeat unit of formula (I) and the curable material and curing the precursor film.

[0141] Curing may be performed by light treatment, preferably UV light treatment, and I or heat treatment. Curing conditions (time and temperature) may be selected according to the materials of the precursor film. Optionally, curing is in the range of 20-80 °C. In the case of low-temperature curing (e.g. below 30 °C), the curing time is preferably at least 12 hours.

[0142] In the case where a curing agent is reacted with the curable material, the curing agent is preferably added to the composition comprising the polymer comprising the repeat unit of formula (I) and the curable material prior to deposition of the composition. The curing agent is suitably a separate material from the curable material and the polymer comprising the repeat unit of formula (I).

[0143] Formation of the precursor film may comprise deposition of a formulation comprising the polymer comprising the repeat unit of formula (I), the curable material and any other components of the composition dissolved or dispersed in one or more solvents, followed by evaporation of the solvent or solvents. Formation of the precursor film may comprise solvent-free deposition of the composition in liquid form. Optionally, the curable material and, optionally, one or more curing agents are the only material of the formulation which are liquid at 25°C and atmospheric pressure.

[0144] The solvent or solvents of the solution may be selected according to their ability to dissolve the polymer, the curable material and, if present, the curing agent and include, without limitation, benzene or naphthalene substituted with one or more substituents, optionally one or more substituents selected from C1-12 alkyl, C1-12 alkoxy, F and Cl; ethers; esters; halogenated alkanes; ketones; sulfoxides; and mixtures thereof. Exemplary solvents include, without limitation, toluene, xylenes, 1,2,4-trimethylbenzene, mesitylene, 1-methylnaphthalene, 1-chloronaphthalene, anisole, tetrahydrofuran, N-methylpyrrolidone, 1,2-dimethoxybenzene, dimethylsulfoxide l,3-dimethyl-2-imidazolidinone, 1,2-dichlorobenzene and cyclopentanone.

[0145] The concentration of each material dissolved in the formulation is preferably in the range of about 1-500 mg I ml, more preferably about 10-40 mg I ml.

[0146] The formulation may be deposited by any known solution processing material including, without limitation, spin-coating, dip-coating, jet dispensing, drop-casting, spray coating and blade coating.

[0147] Formation of the precursor film may comprise deposition of a melt comprising the polymer comprising the repeat unit of formula (I) and the curable material, wherein the melting point of the composition is lower than its curing temperature.

[0148] A melt may be processed using any known thermal processing technique, for example extrusion, injection moulding, compression moulding, thermocompressive bonding and hot press or melt press moulding.

[0149] Optionally, a cured film comprising or consisting of a cured composition as described herein has a thickness in the range of 1-100 microns, preferably 5-100 microns.

[0150] Applications

[0151] A film comprising a curable composition as described herein may be used in any known application of a thermally conductive film. The film as described herein may be disposed between a surface of a heat-generating component and a heat dispersing component of a system, such as in any known thermal interface management application.

[0152] It will be understood that in this arrangement the film is configured to transfer heat from the heat-generating component to the heat-dispersing component. The film preferably has a first surface in direct contact with a surface of the heat-generating component and I or a second surface opposing the first surface in direct contact with a surface of the heatdispersing component.

[0153] The heat-generating component of the system may be an electronic device.

[0154] Any passive or active heat transfer component known to the skilled person may be used including, without limitation, a heat sink having a surface in contact with the film and an opposing surface comprising one or more heat-dissipating features, for example fins or a pipe or channel configured to transfer heat to a fluid flowing through the pipe or channel. The fluid may or may not undergo a phase change upon absorption of heat.

[0155] Preferably, the film is a thermally conductive layer of an electronic device.

[0156] Heat may be transferred from a surface by bringing a layer comprising a thermally conductive film as described herein adjacent to the surface. The thermally conductive film may be in direct contact with the surface or it may be spaced apart from the surface by one or more thermally conductive layers.

[0157] A film as described herein may be disposed on a surface of a heat sink opposing a surface of the heat sink having fins extending therefrom. In use, the film may be disposed between the heat sink and an electrical component.

[0158] A film as described herein may be a heat spreader layer disposed on a surface of a printed circuit board, for example a PCB for use in LED arrays.

[0159] A film as described herein may be used as an electrically non-conductive film, e.g. an underfill, between opposing surfaces of electrically connected layers, e.g. between a substrate and a semiconducting wafer or between two semiconducting wafers, such as for a flip chip including but not limited to 3D stacked multi-chips. The curable composition may be introduced between the two layers by any method known to the skilled person, for example a capillary underfill method or pre-applied underfill method. Following formation of the film comprising the curable composition, the film may be heated to above a melting point of the curable composition. Following alignment and bonding between the opposing surfaces, the film may be heated to a curing temperature above the melting point to form a solid, crosslinked film.

[0160] Following curing, the structure may be diced. Dicing may be performed using any method known to the skilled person.

[0161] Figure 1 illustrates a 3D stack of chips 105 according to some embodiments, wherein the chips 105 are interposed by an interposer 111 and a non-electrically conductive film 109 disposed between adjacent interposer and chip surfaces and between the substrate 101, e.g. a printed circuit board, and a first chip of the 3D stack. At least one non-electrically conductive film 109 comprises a polymer as described herein. Through-vias 115 are formed through the chips 105 and the interposers. The 3D stack may comprise a heat sink 113 disposed on a surface thereof.

[0162] In formation of the 3D stack, a first non-electrically conductive film 109 may be formed by deposition of a curable polymer as described herein followed by curing of the film prior to or after formation of one or more further non-electrically conductive films 109. Following curing, the film is stable to elevated temperatures that may be used in subsequent processing steps, for example formation of the one or more further non-electrically conductive films 109. Preferably, a plurality of the non-electrically conductive films 109 comprise or consist of a crosslinked composition as described herein.

[0163] In some embodiments, a film comprising or consisting of a crosslinked composition as described herein may be disposed between an electronic device and a heat sink.

[0164] EXAMPLES

[0165] Thermal conductivity measurement

[0166] A sensor substrate 600 (ca. 25 mm x 25 mm) illustrated in Figure 2 was used for measurement of thermal conductivity as described herein. The substrate has a polyimide (PI) film (25 microns) with a 400 nm thick heating structure consisting of a 20 micron wide heater line 610, 500 micron wide busbars 620 for application of a current and contact pads 640. A sensing structure mirrors the heating structure except that the heater line is replaced with a 200 micron wide sensor line 630.

[0167] With reference to Figures 3A and 3B, the sensor substrate 600 carrying the film to be measured is placed on a temperature-controlled aluminium block, regulated via a PID system such that the temperature may be controlled by software. The aluminium block has a long notch 720 of 1 mm width and ~1 mm depth cut into it. The sensor substrate 600 is placed over the notch such that the central heater line 610 is aligned with the centre of the notch 720, and the sensor line 630 is aligned with the edge of the notch. A PMMA sheet 730 (2 mm thickness) with a notch cut-through matching that of the aluminium block 710 is placed over the top and an addition piece of plain PMMA sheet 740 (5 mm thickness) is placed on top to enclose the device. The entire assembly is clamped using bolts and nuts at positions 750. The heater line is connected to a sourcemeter unit (Keithley 2400) using a 4-wire measurement set up. The sensor line is connected to a multimeter unit (Keithley 2001) using a 4-wire set up.

[0168] The temperature of the assembly is first stabilised at a predetermined temperature. The resistance of the heater line and the temperature sensor is then measured. To measure the resistance of the heater line without causing undue heating a low current is sourced and voltage measured in short pulses, with time allowed between pulses for heat to be dissipated. A constant DC current is then passed along the heater line to cause resistive heating. The arrangement of the substrate in the assembly causes heat to flow through the substrate and film to the aluminium block which acts as a heat sink, setting up an approximate one-dimensional steady state heat flux. The power dissipated in the heater line, and the resistance of the heater line and temperature sensor is additionally measured in this state. This process is repeated for increasing sourced current, and the complete process repeated at the next temperature setpoint.

[0169] The resistances of the heater line and sensor lines under the condition of no heat flux at different temperature setpoints are used as calibration data in a straight-line fit of resistance and temperature, allowing the temperature of the resistive elements to be determined under the condition of steady state heat flux. As such the temperature gradient, AT, between the heater line and temperature sensor (aligned with the heatsink) can then be calculated. The power dissipated in the heater line is assumed to be completely converted to heat energy Q. A straight-line fit is then made between dT and Q with additional parameters for the length of the heater line over which power is measured (L, 14 mm), the distance between the voltage sense points) and the gap width (2 w, 1 mm). This provides a measure of the conductance C of the device under test and is affected by losses pertaining to conductive heat transfer in the substrate and convective and radiative heat transfer to the environment (h).

[0170] To calculate a thermal conductivity K, the same measurement process is carried out on substrates without any test film (substrate only). We assume the losses will be approximately the same when measuring a coated vs uncoated substrate. We subtract the conductance of the substrate (Cs) from the device measurement (CF+S) to adjust for these losses. The thermal conductivity (kp) is then calculated by dividing the resulting film only conductance by the film thickness (dp). The film thickness is determined using a digital micrometer by measuring the total thickness and subtracting the substrate thickness.

[0171]

[0172] PEG diglycidyl ether (Mn~500) and branched PEI (Mw~600) were separately dissolved in 1,2-dichlorobenzene at a concentration of 20 mg / ml at room temperature.

[0173] Polymer 1 was dissolved in 1,2-dichlorobenzene at a concentration of 20 mg / ml at 80 °C and the solution was left to cool down to room temperature.

[0174] Boron nitride (BN) nanoflakes were prepared via a ball milling process. BN powder (2.76 g, Goodfellow, nominal particle size 10 microns) was placed in a zirconia lined milling jar (50 mL) with zirconia milling beads (114 g, 2 mm) and 2M aqueous NaOH (15.1 g). The mixture was milled in a planetary ball mill (Retsch PM100) at 400 rpm for 6 hours. On completion the mixture was decanted from the milling jar and washed with deionised water. The milling beads were separated by sieving. The boron nitride nanoflakes were collected by filtration using a small pore filter, washing with water until the filtrate was neutral, then with methanol and dried in air at 130 °C to yield 2.47 g as white solid. The milled BN was functionalized by reaction with 2',5'-dihexyloxy terphenyl 4,4"-dialdehyde.

[0175] 0.5 g of BN prepared above was dispersed in 100 ml DMSO with 0.593 g of 2',5'-dihexyloxy terphenyl 4,4"-dialdehyde. The reaction mixture was stirred for 20 hours at 100 °C. The product was collected via filtration and washed with acetone and toluene to remove unreacted aldehyde. The solid was dried for 4 hours at 100 °C to yield 0.44 g of lightyellow solid which was then suspended in 1,2-dichlorobenzene at a concentration of 20 mg / ml. The suspension was homogenised by sonication (Fisherbrand 11207, 100 % duty cycle, 37 kHz, 50 °C) for 1 hour. The suspension was then cooled down to room temperature.

[0176] Solutions and suspension were mixed as set out in Table 1 and further homogenised using a vortex mixer. The solutions (if no BN is present) or suspensions (if BN is present) were then drop casted onto polyimide substrates and dried in ambient environment overnight. The films were then cured at 170 °C for 1 hour, and then transferred to thermal conductivity testing.

[0177]

[0178] ,

[0179]

[0180] Branched polyethylenimine (PEI), (Mw 600)

[0181] Table 1: weight ratios for polymer blends

[0182]

[0183] Table 2: weight ratios for polymer blends with functionalised BN

[0184]

[0185] With reference to Table 1, thermal conductivity increases with increasing amounts of Polymer 1.

[0186] Thermal conductivity of a film formed from comparative formulation 6 of PEG diglycidyl ether / PEI only was not measured due to shrinkage of the film formed from this formulation, whereas films formed from formulations containing Polymer 1 underwent less or no shrinkage showing an advantage in terms of film formation.

[0187] With reference to Table 2, highest thermal conductivities were obtained from formulations containing both Polymer 1 and PEG diglycidyl ether I PEL Surprisingly, the film formed from formulation 11, containing 60 wt% Polymer 1 and no PEG diglycidyl ether / PEI, has lower thermal conductivity than films formed from formulations 9 and 10 which contain lower amounts of Polymer 1. This indicates that presence of both Polymer 1 and the PEG diglycidyl ether / PEI contribute to increased thermal conductivity in films containing BN filler particles.

[0188] Composition Examples - aromatic epoxy

[0189] MG Chemicals 832C Translucent Epoxy Encapsulating and Potting Compound (MG-832C) epoxy Part A and Part B (triethylenetetramine) were separately dissolved in 1,2-dichlorobenzene at a concentration of 20 mg / ml at room temperature.

[0190] Polymer 1 was dissolved in 1,2-dichlorobenzene at 20 mg / ml at 80 °C and cooled down to room temperature. The solution was mixed with Part A and Part B in ratios set out in Table 3 with the MG-832C Part B solution added last, and homogenised using a vortex mixer. The solutions were then drop-cast onto a heated polyimide substrate at 65 °C and dried at 65 °C for 1 hour. The films were then cured at 170 °C for 30 minutes before transferred to thermal conductivity testing.

[0191] Table 3

[0192]

[0193]

[0194] With reference to Table 3, thermal conductivity increases with increasing amounts of Polymer 1.

[0195] Further films were formed as described above using formulations containing MG-832C except that Polymer 1 was replaced with one of Polymers 2-4, illustrated below, and the Polymer: MG-832C ratio was 9:1 by mass, in which the Part A: Part B ratio of MG-832C was 2:1 by mass.

[0196]

[0197] For comparison, thermal conductivities of neat films containing Polymers 2-4 only were measured.

[0198] Results are set out in Table 4.

[0199] Table 4

[0200]

[0201] Films containing epoxy and Polymer 1 or 4 all have very similar thermal conductivities, despite a much wider range of thermal conductivities for neat films of these polymers. Films containing epoxy and Polymer 2 or 3 maintain a higher conductivity than any of the corresponding films containing epoxy and Polymer 1 or 4. Without wishing to be bound by any theory, this may be due to higher rigidity of Polymers 2 and 3 due to their shorter linker group (Polymers 2 and 3 have a -(C2H4)- linker group and Polymers 1 and 4 have a -(OC5H10O)- linker group).

[0202] Further films were formed with Polymer Examples 1, 3, 5, 6 and 7 using more concentrated solutions to obtain thicker films. MG Chemicals 832C Translucent Epoxy Encapsulating and Potting Compound (MG-832C) epoxy Part A and Part B (hardener) were separately dissolved in 1,2-dichlorobenzene at a concentration of 30 mg / ml at room temperature. Polymers were separately dissolved in 1,2-dichlorobenzene at 30 mg / ml at 80°C and cooled down to room temperature. The polymer solutions were mixed with Part A and Part B solutions in ratios set out in Table 5 with the MG-832C Part B solution added last, and homogenised using a vortex mixer. The solutions were then drop-cast onto a heated polyimide substrate at 65°C and dried at 65°C for 1 hour. The films were then cured at 170°C for 1 hour before transferred to thermal conductivity testing.

[0203]

[0204]

[0205] Polymer 6

[0206]

[0207] Polymer 7 Table 5:

[0208]

[0209] With reference to Table 5, thermal conductivity increases with increasing amounts of polyimines.

Claims

CLAIMS1. A composition comprising a polymer comprising a repeat unit of formula (I) and at least one of a curable material comprising a plurality of crosslinkable groups and a curing agent capable of reacting with a crosslinkable material to form a crosslinked network:wherein:X1and X2are each independently selected from formulae (II) and (III):-(Ar^m Formula (II)-(Ar2)P-L-(Ar3)q- Formula (III)wherein Ar1, Ar2and Ar3in each occurrence is an arylene or heteroarylene group; m is at least 1; p is 0, 1, 2 or 3; q is 0, 1, 2 or 3, and L is selected from O, S, C=O, COO, CONR5, NR5, Si(R5)2 C(R7)2 and an optionally substituted chain of methylene (-CH2-) groups wherein one or more non-adjacent methylene groups may be replaced with O, S, C=O, COO, CONR5, NR5or Si(R5)2 wherein R5is H or a substituent; each R5is independently a substituent; and each R7is independently a substituent;one of Y1and Y2is CR1wherein R1is H or a substituent; and the other of Y1and Y2is N; andone of Y3and Y4is CR1; and the other of Y3and Y4is N.

2. The composition according to claim 1 wherein the curable material comprises a plurality of crosslinkable groups selected from:an acyclic unit of formula -CR10=CH2 wherein R10is H or a substituent;a cyclic alkene unit;an optionally substituted epoxide unit;an optionally substituted oxetane unit; andan optionally substituted benzocyclobutene unit.

3. The composition according to claim 2 wherein the curable material comprises a plurality of optionally substituted epoxide units.

4. The composition according to claim 3 wherein the composition further comprises a curing agent comprising a plurality of amine groups.

5. The composition according to claim 4 wherein the curing agent is a branched polyethyleneimine.

6. The composition according to any one of the preceding claims wherein the curable material is a polymerisable monomer.

7. The composition according to any one of the preceding claims wherein the curable material is a curable polymer.

8. The composition according to any one of the preceding claims wherein the curable polymer comprises a repeat unit comprising an alkylene-oxy group.

9. The composition according to any one of the preceding claims wherein Y1and Y4are both the same one of CR1and N; and Y2and Y3are both the same and are the other one of CR1and N.

10. The composition according to any one of the preceding claims wherein Ar1, Ar2and Ar3are each, independently in each occurrence, selected from a 6-12 membered arylene or an optionally fused 5- or 6-membered heteroarylene.

11. The composition according to any one of the preceding claims wherein Ar1, Ar2and Ar3independently in each occurrence is an unsubstituted or substituted paraphenylene.

12. The composition according to any one of the preceding claims wherein p and q are each 1.

13. The composition according to any one of the preceding claims wherein the composition consists of the polymer and the curable material.

14. The composition according to any one of claims 1-13 wherein the composition further comprises a thermally conductive particulate material.

15. A formulation comprising the composition according to any one of the preceding claims and one or more solvents wherein the curable material and the polymer are dissolved in the one or more solvents.

16. A method of forming a cured structure comprising curing a composition according to any one of claims 1-14 wherein the composition comprises the curable material and the polymer.

17. The method according to claim 16 wherein the composition further comprises the curing agent.

18. A film comprising a composition according to any one of claims 1-14.

19. A cured film comprising a composition according to any one of claims 1-14 in which the curable material has been cured.

20. A method of forming a film according to claim 19 wherein the film is formed by a thermal processing method.

21. The method according to claim 20 wherein the thermal processing method is selected from extrusion, injection moulding, thermocompressive bonding and hot press or melt press moulding.

22. An electronic device comprising a film according to claim 19 disposed on a surface of a functional layer of the electronic device.

23. The electronic device according to claim 22 wherein the film is disposed in a region between the surface of the functional layer and a first surface of a first chip electrically connected to the functional layer.

24. The electronic device according to claim 23 wherein the functional layer is a printed circuit board; an interposer; or a second chip.

25. The electronic device according to any one of claims 22-24 wherein the electronic device comprises a plurality of films according to claim 19.

26. The electronic device according to any one of claims 22-25 wherein the electronic device comprises a 3D chip stack.

27. Apparatus comprising a heat-generating device, a heat transfer device configured to transfer heat away from the heat-generating device and a film according to claim 19 disposed between the heat-generating device and the heat transfer device.

28. A heat sink comprising a first surface having fins extending therefrom and an opposing second surface having a film according to claim 19 disposed thereon.29

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