Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
  • C09K5/08—Materials not undergoing a change of physical state when used
  • C09K5/14—Solid materials, e.g. powdery or granular

Definitions

• the present disclosure relates to a two-part thermal interface material based on a polysulfide resin and a plurality of thermally conductive fillers.
• the present disclosure further relates to an electronic device comprising the two-part thermal interface material.
• Electronic devices such as integrated circuits (IC), central processing units (CPU), and power modules typically generate a significant amount of heat during operation.
• heat generated by the electronic device during use is transferred from a heat source of the device to a heat sink, where the heat is harmlessly dissipated.
• Thermal interface materials also known as TIM or TIMs, provide an intimate contact between the heat sink and the heat source to facilitate heat transfer between the two.
• the TIMs have an important impact in a device’s operation, both in performance and reliability. These materials can be used to accelerate heat dissipation and provide cost-effective method to reduce overall size of the package.
• TIMs can be based on metal, ceramics or polymer composites.
• Thermal paste also called thermal grease or thermal compound
• thermal grease are the most common TIMs. These one-component materials effectively bridge the gap between the heat source and heat sink, eliminate micro air pockets, and as a result, provide low thermal resistance initially. The biggest challenge with these materials, however, is migration and voiding over time, causing reduction in thermal conductivity and as well as contamination in the surrounding areas.
• thermal pads Another type of TIMs is thermal pads, which are commonly pre-cured and pre-cut. Pads address the handling and application challenges of the pastes. In order to achieve effective heat transfer, the thermal pads should be designed to have Shore OO Hardness less than 90 to minimize the mechanical stress and to improve surface contact between heat components and thermal pads.
• Reactive gap filler TIMs are cure-in-place materials, which are typically applied as a two-component paste and grows in molecular weight and cures into a solid pad. Compared to conventional pre-cured and pre-cut thermal pads, these gap fillers can adopt to the irregular surface terrain of the substrates, thus creating a more intimate contact without adding additional external pressure between the substrates.
• Traditional gap fillers are silicone-based since they provide good thermal conductivity and softness. However, silicone-based materials are often associated with bleeding and outgassing due to low molecular weight cyclics, free/unreacted silicone chains, as well as decomposition during thermal aging. This often leads to device contaminations, as well as loss of intimate contact.
• a composition comprising a polysulfide resin is provided.
• the polysulfide resin is prepared from two parts, and upon mixing the two parts, polysulfide resin is cured.
• a plurality of thermally conductive fillers is added and dispersed throughout the polysulfide resin to provide thermal conductivity, which may be used as a TIM.
• the polysulfide resin has a predominantly comb-like network structure, where the main backbone structure is formed by reacting an acrylate resin and a thiol resin, and at least one of the resins contains (i) a difunctional group and (ii) a chain having glass transition temperature less than -20°C, preferably less than -30°C.
• the side chain, comb portion of the network structure is formed through a thiol-acrylate reaction with a monofunctional acrylate or thiol resin having a molecular weight over 100 g/mol, preferably over 200 g/mol.
• the comb network structure is formed through Scheme I.
• a tri thiol resin is reacted with a di-acrylate resin to form the backbone.
• One of the thiol functional groups from the tri-thiol resin is reacted with a mono-acrylate resin to form the comb side chain.
• One part comprises the tri-thiol resin and the other part comprises the diacrylate resin.
• the mono-acrylate resin may be in either of the parts.
• the two parts have equal weight and equal molar amounts of each functionality, thiols and acrylates. Upon combining the two parts, the polysulfide resin is formed.
• Scheme II is another embodiment of the invention.
• the thiol and acrylate functionalities of the resins is switched from Scheme I for this reaction.
• a tri-acrylate resin is reacted with a di-thiol resin to form the backbone.
• One of the acrylate functional groups from the tri-acrylate resin is reacted with a mono-thiol resin to form the comb side chains.
• One part comprises the tri-acrylate resin and the other part comprises the dithiol resin.
• the mono thiol resin may be in either of the parts.
• the two parts have equal weight and equal molar amounts of each functionality, thiols and acrylates. Upon combining the two parts, the polysulfide resin is formed.
• Monothiol Monothiol
• a tetrafunctional thiol, in combination of two mono acrylate and di-acrylate is reacted used to form the polysulfide resin, as shown in Scheme III.
• One part comprises the tetra-thiol resin and the other part comprises the diacrylate resin.
• the two mono-acrylate resins may be in either of the parts.
• the two parts have equal weight and equal molar amounts of each functionality, thiols and acrylates.
• the polysulfide resin is formed.
• polysulfide resin may be formed by flipping the acrylate functionality and thiol functionality in each of the resins described in Scheme III, i.e. , a reaction of a tetrafunctional acrylate, in combination of two mono-thiols and di-thiol resins.
• One part comprises the tetra-acrylate resin and the other part comprises the dithiol resin.
• the two mono thiol resins may be in either of the parts.
• the two parts have equal weight and equal molar amounts of each functionality, thiols and acrylates. Upon combining the two parts, the polysulfide resin is formed.
• the comb network may be formed by reacting three di-thiols in combination with a mono-acrylate, a di-acrylate, and a tri-acrylate resins, as shown in Scheme IV.
• One part comprises all acrylate-based resins and the other part comprises all thiol- based resins.
• one part comprises diacrylate and the other part comprises tri-acrylate and di-thols.
• the mono-acrylate may be in either parts. The two parts have equal weight and equal molar amounts of each functionality, thiols and acrylates. Upon combining the two parts, the polysulfide resin is formed.
• the polysulfide resin may be formed by flipping the acrylate functionality and thiol functionality in each of the resins described in Scheme IV, i.e., a reaction of di-acrylate in combination with a mono-thiol, a di-thiol, and a tri-thiol resin.
• One part comprises all acrylate-based resins and the other part comprises all thiol- based resins.
• one part comprises dithiols and the other part comprises tri-thiols and di-acrylates.
• the mono-acrylate may be in either parts.
• the two parts have equal weight and equal molar amounts of each functionality, thiols and acrylates. Upon combining the two parts, the polysulfide resin is formed.
• the polysulfide resin is formed by combining two separate parts: Part A and Part B. Upon mixing the two parts, and optionally with the addition of catalysts in either Part A or B, both parts react to form the comb-like structure. It is preferred that at least one of the Part A or Part B further comprises a plurality of thermally conductive fillers.
• Another aspect of the present invention provides an electronic device containing a heat source, a heat sink and a TIM prepared with the polysulfide resin according to the above description disposed therebetween.
• Figure 1 is a modulus and tan d of a polysulfide resin filled with thermally conductive fillers prepared in accordance with the invention.
• the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.”
• the terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps.
• compositions or processes as “consisting of and “consisting essentially of the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom, and excludes other ingredients/steps.
• the approximating language may correspond to the precision of an instrument for measuring the value.
• the modifier "about” should also be considered as disclosing the range defined by the absolute values of the two endpoints.
• the expression “from about 2 to about 4" also discloses the range “from 2 to 4.”
• the term “about” may refer to plus or minus 10% of the indicated number.
• “about 10%” may indicate a range of 9% to 11%”
• “about 1” may mean from 0.9-1.1.
• Other meanings of "about” may be apparent from the context, such as rounding off, so, for example "about 1” may also mean from 0.5 to 1.4.
• a resin, oligomer or monomers are used interchangeably here in the invention.
• Acrylate is broadly defined as including acrylates, substituted acrylate, e.g., (meth)acrylates.
• a plurality of thermally conductive fillers may be dispersed throughout the polysulfide resin to provide thermal conductivity for use as a TIM.
• the mono-acrylate pendent comb unit is linked to the main backbone through the residual thiol group. It has been determined that the pendant groups (1) minimize leaching or migration without the inclusion of a plasticizer, and (2) achieve low Shore OO Hardness without the addition of any floating resin components to the polysulfide polymer.
• multifunctional thiols and multifunctional acrylates remain in separate Part A or Part B, until combined together to form the polysulfide resin.
• the di-acrylates useful to prepare the polysulfide resin include functionalized di acrylate having a Tg value less than -20°C, preferably less than -30°C.
• exemplary functionalized acrylates are polyether-based acrylate, e.g., polypropylene glycol di-acrylate, polyethylene glycol di-acrylate, polytrimethylene glycol di-acrylate, polytetramethylene glycol di acrylate, and the like.
• the functionalized di-acrylate has a molecular weight in the range of about 200 to about 2000 g/mol.
• di-acrylates might be prepared from a low Tg diol backbone such as 2-methyl-1, 3-propanediol adipate, polybutadiene diol, hydrogenated polybutadiene diol, polyfarnesene diol, dimer diol along with its polyester oligomer diols.
• Non-limiting exemplary di-acrylates include polypropylene glycol diacrylate, having a Tg of -25°C and molecular weight of 205 and Tg of -48°C and molecular weight of 585, available from Miwon Specialty Chemical as Miramer 2040 and 2070, respectively.
• the tri-acrylate resin examples include trimethylolpropane tri-acrylate, pentaerythritol tri-acrylate, glycerin tri-acrylate, and those chain-extended with ethylene oxide (EO), or propylene oxide (PO) units such as trimethylolpropane (EO) m tri-acrylate, trimethylolpropane (PO) n tri-acrylate, glycerin (PO) n tri-acrylate, and the like. All backbones for di-acrylates can be used for tri-acrylates.
• the mono-acrylate resins suitable for this include, but not limited to long chain alkyl acrylates (such as lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, linear or branched stearyl acrylate), polyester mono-acrylate such as caprolactone acrylate, polypropylene oxide mono acrylate, and nonyl phenol based acrylates chain-extended with ethylene oxide (EO), or propylene oxide (PO) units such as nonyl phenol (EO) m acrylate, nonyl phenol (PO) n acrylate.
• long chain alkyl acrylates such as lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, linear or branched stearyl acrylate
• polyester mono-acrylate such as caprolactone acrylate, polypropylene oxide mono acrylate, and nonyl phenol based acrylates chain-extended with ethylene oxide (EO), or
• the mono-acrylate resins are added in order to adjust thiol to acrylate ratio, balance weight and volume of the first and second part, and reduce hardness of the cured networks.
• the mono acrylate resin may be added to either the first part or the second part.
• the above groups may be further substituted or with heteroatoms such as halogens, oxygens, sulfur and nitrogens.
• the above groups may be unsaturated.
• the thiol resin useful for preparing the polysulfide resin include mono-thiols such as poly(ethylene glycol) methyl ether thiol, alkyl thiols or alkyl 3-mercaptopropionates wherein the alkyl group has linear or branched C1 to C30 backbone.
• alkyl refers to a monovalent linear, cyclic or branched moiety containing C1 to C30 carbon and only single bonds between carbon atoms in the moiety and including, for example, include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, hexadecyl, octadecyl groups.
• the above thiol resin may be further substituted with heteroatoms such as halogens, oxygens, sulfur and nitrogens. Also, the above groups may be unsaturated.
• the mono-thiol resins may be incorporated in the first or the second part.
• the multifunctional thiol resin includes at least two thiol groups in the resin, and preferably, the multifunctional thiol has a molecular weight in the range of about 100 to about 1000 g/mol.
• Non limiting examples of multifunctional thiol resin include 2,2'-(ethylenedioxy) diethanethiol, also known as DMDO (1,8-dimercapto-3,6-dioxaoctane), dipentene dimercaptan, POLYTHIOLTM QE-340M from Toray Fine Chemicals, HS series Mercaptan from Hampton Fine Chemical, Karenz MTTM PE1 , NR1, BD1 product lines from Showa Denko. Thiol-functional siloxane copolymers such as SMS series from Gelest may also be considered.
• the thiol has a molecular weight in the range of about 100 to about 1000 g/mol.
• Preferred multifunctional thiol has a trifunctional core of trimethylolethane, trimethylolpropane or glycerin.
• Exemplary thiol resins include, but not limited to, trimethylolpropane tris(3-mercaptopropionate) (V) and pentaerythritol tetrakis(3-mercaptopropionate) (VI).
• the balance between the components can be adjusted to change the hardness of the composition.
• the effectiveness of the thermal interface material to transfer heat is significantly impacted by the interface between the TIM and the heat source and a soft, conformable material can optimize the contact at the interface.
• the ratio of the acrylate to the thiol resins ranges from about 1.0 : 0.8 to about 1.2 : 1.0.
• the Shore OO Hardness, measured at 24 hours at 22-25°C, of the polysulfide resin is from about 1 to about 90.
• the resin is a soft, conformable material that can optimize the contact at the interface, which it is placed onto.
• compositions for use as a TIM further includes a plurality of thermally conductive fillers.
• the filler can be included in the first part, the second part, or both the first and second parts.
• Thermally conductive fillers are known in the art and commercially available, see for example, U.S. Pat. No. 6,169,142 (col. 4, lines 7-33).
• the thermally conductive filler may be both thermally conductive and electrically conductive.
• thermally conductive filler may be thermally conductive and electrically insulating.
• useful thermally conductive fillers may comprise a metallic filler, an inorganic filler, a carbon-based filler, a thermally conductive polymer particle filler, or a combination thereof.
• Metallic fillers include particles of metals and particles of metals having layers on the surfaces of the particles. These layers may be, for example, metal nitride layers or metal oxide layers on the surfaces of the particles. Suitable metallic fillers are exemplified by particles of metals selected from the group comprising aluminum, copper, gold, nickel, silver, and combinations thereof. Suitable metallic fillers are further exemplified by particles of the metals listed above having layers on their surfaces selected from the group comprising aluminum nitride, aluminum oxide, copper oxide, nickel oxide, silver oxide, and combinations thereof. For example, the metallic filler may comprise aluminum particles having aluminum oxide layers on their surfaces.
• Inorganic fillers can include metal oxides such as aluminum oxide, beryllium oxide, magnesium oxide, and zinc oxide; nitrides such as aluminum nitride and boron nitride; carbides such as silicon carbide and tungsten carbide; and combinations thereof.
• metal oxides such as aluminum oxide, beryllium oxide, magnesium oxide, and zinc oxide
• nitrides such as aluminum nitride and boron nitride
• carbides such as silicon carbide and tungsten carbide
• Other examples include aluminum trihydrate, silicone dioxide, barium titanate, magnesium hydroxide.
• Carbon-based fillers can include carbon fibers, diamond, graphite.
• Carbon nanostructured materials such as one-dimensional carbon nanotubes (CNTs) and two- dimensional (2D) graphene and graphite nanoplatelets (GNPs) could also be used in the composition due to their high intrinsic thermal conductivity.
• thermally conductive polymer fillers examples include oriented polyethylene fibers and nanocellulose.
• Other examples of polymers that could be used to make thermally conductive fillers include polythiophene, liquid crystalline polymers based on polyesters or epoxies, etc.
• Thermally conductive filler particles is not restricted; however, rounded or spherical particles may prevent viscosity increase to an undesirable level upon high loading of thermally conductive filler in the composition.
• Thermally conductive filler may be a single thermally conductive filler or a combination of two or more thermally conductive fillers that differ in at least one property such as particle shape, average particle size, particle size distribution, and type of filler.
• a combination of inorganic fillers such as a first aluminum oxide having a larger average particle size and a second aluminum oxide having a smaller average particle size can be included in the composition.
• a combination of an aluminum oxide having a larger average particle size with a zinc oxide having a smaller average particle size can be included in the composition.
• Combinations of metallic fillers such as a first aluminum having a larger average particle size and a second aluminum having a smaller average particle size can alternatively be included in the composition.
• combinations of metallic and inorganic fillers such as a combination of aluminum and aluminum oxide fillers; a combination of aluminum and zinc oxide fillers; or a combination of aluminum, aluminum oxide, and zinc oxide fillers can alternatively be included in the compositions disclosed herein.
• the use of a first filler having a larger average particle size and a second filler having a smaller average particle size than the first filler may improve packing efficiency, may reduce viscosity, and may enhance heat transfer.
• the thermally conductive filler may also include a filler treating agent.
• the filler treating agent may be any treating agent known in the art.
• the amount of filler treating agent may vary depending on various factors including the type and amounts of thermally conductive fillers.
• the filler treating agent will be included in the composition in an amount in the range of about 0.1 wt.% to about 5.0 wt.% of the filler.
• the filler may be treated with filler treating agent in situ or pretreated before being combined with the resin to make the composite.
• the filler treating agent may comprise a silane such as an alkoxysilane, an alkoxy-functionalized oligosiloxane, a cyclic polyorganosiloxane, a hydroxyl-functionalized oligosiloxane such as a dimethyl siloxane or methyl phenyl siloxane, a stearate, or a fatty acid.
• Alkoxysilane filler treating agents are known to the art and are exemplified by hexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetradecyltrimethoxysilane, phenyltrimethoxysilane, phenylethyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, and a combination thereof.
• the filler treating agent can be any organosilicon compounds typically used to treat silica fillers.
• organosilicon compounds include, but are not limited to, organochlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, and trimethyl monochiorosilane; organosiloxanes such as hydroxy-endblocked dimethylsiloxane oligomer, hexamethyldisiloxane, and tetramethyldivinyldisiloxane; organosilazanes such as hexamethyldisilazane and hexamethylcyclotrisilazane; and organoalkoxysilanes such as methyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3- glycidoxypropyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane.
• a polyorganosiloxane capable of hydrogen bonding is useful as a filler treating agent.
• the filler in addition to thermally conductive filler, may also comprise a reinforcing filler, an extending filler, or a combination thereof.
• the thermally conductive filler material for use in the composition disclosed herein is selected from the group comprising aluminum oxide, boron nitride, aluminum nitride, magnesium oxide, zinc oxide, or a combination thereof.
• CB-A205 and AI-43-Me are aluminum oxide fillers of differing particle sizes commercially available from Showa-Denko
• DAW-45 is aluminum oxide filler commercially available from Denka
• AA-04, AA-2, and AA18 are aluminum oxide fillers commercially available from Sumitomo Chemical Company.
• Zinc oxides are available from Zochem LLC.
• suitable fillers and/or additives may also be added to the compositions disclosed herein to achieve various composition properties.
• additional components include pigments, plasticizers, process aids, flame retardants, extenders, electromagnetic interference (EMI) or microwave absorbers, electrically conductive fillers, magnetic particles, etc.
• EMI electromagnetic interference
• a wide range of materials may be added to a TIM according to exemplary embodiments, such as carbonyl iron, iron silicide, iron particles, iron-chrome compounds, metallic silver, carbonyl iron powder, SENDUST (an alloy containing 85% iron, 9.5% silicon and 5.5% aluminum), permalloy (an alloy containing about 20% iron and 80% nickel), ferrites, magnetic alloys, magnetic powders, magnetic flakes, magnetic particles, nickel- based alloys and powders, chrome alloys, and any combinations thereof.
• EMI absorbers formed from one or more of the above materials where the EMI absorbers comprise one or more of granules, spheroids, microspheres, ellipsoids, irregular spheroids, strands, flakes, powder, and/or a combination of any or all of these shapes. Accordingly, some exemplary embodiments may thus include TIMs that include or are based on thermally reversible gels, where the TIMs are also configured (e.g., include or are loaded with EMI or microwave absorbers, electrically conductive fillers, and/or magnetic particles, etc.) to provide shielding.
• thermally conductive filler material is present in the first part of the composition in an amount in the range of about 30-95 wt.%, for example from about 85- 95 wt.% based on the total weight of the first part.
• the thermally conductive filler material is present in the second part in an amount in the range of about 30 wt.% to about 95 wt.%, for example amount from about 85 wt.% to about 95 wt.% based on the total weight of the second part.
• the thermally conductive filler material is present both in the first and the second parts in an amount of about 30 wt.% to about 95 wt.%, and the total weight, based on both parts, of the thermally conductive filler material is present in an amount of about 30 wt.% to about 95 wt.%, preferably from about 85-95 wt.%.
• the acrylate and the thiol resins included in the compositions disclosed herein can react at ambient temperature to form crosslinked/cured polysulfides without the need of a catalyst.
• the optional inclusion of a catalyst in the compositions can effectively speed up the reaction for thiol-acrylate addition.
• one, or several, catalysts can be included in the compositions disclosed herein to tune the curing speed depending on the application and process requirements.
• the acrylate and the thiol resins are each dispensed and then mixed to be reacted. If the catalyzed reaction is too fast, the reactants may clog the dispensing mechanism. If the catalyzed reaction is too slow, the composite may flow out of the area where it is intended to be set after application and contaminate other surrounding components. Accordingly, the reaction speed is critical to obtain the desired properties of the composition.
• Suitable catalysts include base catalyst, but are not limited to, amines, imidazoles, phosphines, and mixtures thereof.
• Radical thermal initiators are also suitable catalysts.
• Non limiting examples of radical thermal initiators include a radical initiator system selected from the group consisting of (a) dibenzoyl peroxide-dimethylaniline mixture, (b) acyl sulfonyl peroxides- dimethylaniline mixture, (c) dibenzoyl peroxide with a reducing agent selected from the group consisting of organoaluminum derivatives, chromium derivatives, tin(ll) derivatives, nitroxyl radicals, benzoyl thiourea; and mixtures thereof, which are described and incorporated herein, Initiators, Free-Radical, Terry N. Myers, 16 November 2001, Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 14
• Exemplary catalysts include HS Mercaptan Epoxy Curing Agent series from Hampton Fine Chemical.
• the catalyst may be chosen to dial-in this efficacy. This is particularly useful for two-part gap filler applications, to allow positioning of the parts, and fully cure within 48, and preferably within 24 hours. This allows time to rework the material to reposition the material without damaging expensive component substrates.
• the composition may optionally further comprise up to about 80 wt.%, by weight of the composition of a liquid plasticizer in the first and/or second part.
• Suitable plasticizers include paraffinic oil, naphthenic oil, aromatic oil, long chain partial ether ester, alkyl monoesters, epoxidized oils, dialkyl diesters, aromatic diesters, alkyl ether monoester, polybutenes, phthalates, benzoates, adipic esters, acrylate and the like.
• Particularly preferred plasticizers include these with functional groups that can further react with either the acrylate or the thiol and be an integral part of the polysulfide network.
• the curable composition further comprises a moisture scavenger.
• a moisture scavenger is selected from the group comprising oxazolidine, p-toluenesulfonyl isocyanate, vinyloxy silane, and combinations thereof p- Toluenesulfonyl isocyanate is a particularly useful moisture scavenger.
• compositions disclosed herein may further optionally comprise up to about 3.0 wt.%, for example about 0.1 wt.% to about 2.5 wt.%, and preferably about 0.2 wt.% to about 2.0 wt.%, by weight of the resin composition in each part, of one or more of an antioxidant or stabilizers.
• Useful stabilizers or antioxidants include, but are not limited to, high molecular weight hindered phenols and multifunctional phenols such as sulfur and phosphorus-containing phenols.
• Hindered phenols are well known to those skilled in the art and may be characterized as phenolic compounds which also contain sterically bulky radicals in close proximity to the phenolic hydroxyl group thereof.
• tertiary butyl groups generally are substituted onto the benzene ring in at least one of the ortho positions relative to the phenolic hydroxyl group.
• hindered phenols include; 1 ,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-benzene; pentaerythrityl tetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate; n-octadecyl-3(3,5-ditert- butyl-4-hydroxyphenyl)-propionate; 4,4'-methylenebis(2,6-tert-butyl-phenol); 4,4'-thiobis(6-tert- butyl-o-cresol); 2,6-di-tertbutylphenol; 6-(4-hydroxyphenoxy)-2,4-bis(n-oct
• Useful antioxidants are commercially available from BASF and include lrganox®565, 1010, 1076 and 1726 which are hindered phenols. These are primary antioxidants that act as radical scavengers and may be used alone or in combination with other antioxidants, such as, phosphite antioxidants like IRGAFOS®168 available from BASF.
• antioxidants and/or stabilizers in the compositions disclosed herein should not affect other properties of the composition.
• One or more retarding agents can also be included in the composition to provide an induction period between the mixing of the two parts of the composite composition and the initiation of the cure.
• the retarding agent can be 8-hydroxyquinoline.
• compositions can be added to the composition, such as for example, nucleating agents, elastomers, colorant, pigments, rheology modifiers, dyestuffs, mold release agents, adhesion promoters, flame retardants, a defoamer, a phase change material, rheology modifier processing aids such as thixotropic agents and internal lubricants, antistatic agents or a mixture thereof which are known to the person skilled in the art and can be selected from a great number of commercially available products as a function of the desired properties.
• nucleating agents elastomers, colorant, pigments, rheology modifiers, dyestuffs, mold release agents, adhesion promoters, flame retardants, a defoamer, a phase change material, rheology modifier processing aids such as thixotropic agents and internal lubricants, antistatic agents or a mixture thereof which are known to the person skilled in the art and can be selected from a great number of commercially available products as
• the composition according to this invention may be used as a TIM to ensure consistent performance and long-term reliability of heat generating electronic devices.
• these compositions can be used as a liquid gap filler material that can conform to intricate topographies, including multi-level surfaces. Due to the increased mobility prior to cure, the composition can fill small air voids, crevices, and holes, reducing overall thermal resistance to the heat generating device. Additionally, thermal interface gap pads can be prepared from this composition.
• dispensing the material from a cartridge can take up to several hours. It is desirable to have a speed of at least 20 g/min for initial dispensing, since this ensures high throughput when the material is applied to an actual device. In addition, 30 to 60 min latency ensures that the mixing area does not get clogged.
• both parts have smiilar densities, but the weights can be adjusted based on the densities of each part to provide the same volume.
• Other volume mixing ratios may also be used, such as 1:2, 1:4, 1:10.
• the thiol:acrylate reactive group ratio is in the range of about 0.8-1.2 : 1.
• the first part and second part of the composition can be mixed to form a composition that can be cured at room temperature.
• the mixed composition has a pot life of longer than about 10 minutes, and preferably longer than about 20 min. It is desirable to have some latency in the first hour after mixing to allow positioning of the parts, and full cure within 24 hours.
• dispensing rate at 30-60 minutes can be adjusted by changing resin stoichiometry, using less catalyst, or moving catalyst from one part to another to minimize pre-reaction between the acrylate and the thiol functionalities.
• the composition after room temperature cure, has a glass transition temperature (Tg) of less than about -20°C, preferably less than about -30°C, and Shore OO Hardness less than about 90, preferably less than about 80, and even more preferably less than about 70, measured at 48 hours. In a preferred emboidment, the same Shore OO Hardness may be achieved in 24 hours. Further, the cured composition is thermally stable from about -40°C to about 125°C
• a stable modulus at elevated temperatures indicate the resin as thermally stable, and the resin can maintain the shape as a TIM in use. Also, the gradual drop of the Tg, instead of sharp decline in G’, denotes heat stability of the cured resin. These characteristics of the resin ensures good dampening performance of the resin to minimize mechanical shock to its attached substrates.
• the polysulfide resin may be formed as a component in an electronic device, e.g., battery, and thus, Shore OO Hardness less than about 90 is desirable since this allows for good damping performance to absorb shocks and minimizes damage in the material, rather than transferring that shock onto expensive battery components. In a preferred embodiment, Shore OO Hardness change of less than 50 is desirable under aggressive aging conditions, e.g., 100°C/2 hours.
• a TIM may include an adhesive layer.
• the adhesive layer may be a thermally conductive adhesive to preserve the overall thermal conductivity.
• the adhesive layer may be used to affix the TIM to an electronic component, heat sink, EMI shield, etc.
• the adhesive layer may be formulated using a pressure-sensitive, thermally conducting adhesive.
• the pressure-sensitive adhesive (PSA) may be generally based on compounds including acrylic, silicone, rubber, and combinations thereof. The thermal conductivity is enhanced, for example, by the inclusion of ceramic powder.
• TIMs including thermally-reversible gel may be attached or affixed (e.g., adhesively bonded, etc.) to one or more portions of an EMI shield, such as to a single piece EMI shield and/or to a cover, lid, frame, or other portion of a multi piece shield, to a discrete EMI shielding wall, etc.
• Alternative affixing methods can also be used such as, for example, mechanical fasteners.
• a TIM that includes thermally-reversible gel may be attached to a removable lid or cover of a multi-piece EMI shield.
• a TIM that includes thermally-reversible gel may be placed, for example, on the inner surface of the cover or lid such that the TIM will be compressively sandwiched between the EMI shield and an electronic component over which the EMI shield is placed.
• a TIM that includes thermally-reversible gel may be placed, for example, on the outer surface of the cover or lid such that the EMI shield is compressively sandwiched between the EMI shield and a heat sink.
• a TIM that includes thermally-reversible gel may be placed on an entire surface of the cover or lid or on less than an entire surface.
• a TIM that includes thermally-reversible gel may be applied at virtually any location at which it would be desirable to have an EMI absorber.
• a device comprising a heat- source, a heat sink, and the compositions disclosed herein disposed therebetween.
• the device does not leave an air gap between the heat source and the heat sink.
• the compositions listed in the following examples were created according to the following procedure.
• the first part (Part A) of the composition was prepared by mixing a di-acrylate and thermally conductive fillers (if used) using a DAC 150 FVZ- K Speedmixer by FlackTek, Inc.
• the second part (Part B) of the composition was prepared by mixing a mono-acrylate, a multifunctional thiol, catalyst, and thermally conductive fillers (if used) using DAC 150 FVZ-K Speedmixer by FlackTek, Inc.
• a polymeric polypropylene glycol (PPG) di-acrylate is chain-extended with a trifunctional thiol resin with a base catalyst, as described in Scheme I, and particularly described as Scheme VII.
• a long chain aliphatic mono-acrylate is linked to the main chain through the residual thiol group, creating a comb structure.
• Cured resins without fillers were obtained by mixing all resins (for one component systems) or Part A with Part B (for two component systems) in a Speedmixer.
• Cured composites (with fillers) were prepared using a Loctite dual cartridge applicator equipped with 50cc or 200cc 2K cartridge and a 6.3-21 static mixer attached to the end of the cartridges.
• Part A and Part B are fully mixed when traveling through the static mixer under applied pressure typically ranging from 0.5 to 0.65 MPa at room temperature.
• Shore OO Hardness was measured using a shore Durometer OO according to ASTM D2240.
• the storage modulus (G’) and tan delta of the composite was measured by Rheometric Scientific RDA III by TA Instruments.
• the dynamic temperature sweep test was performed by placing a composite sample between two parallel plates, then measured from about -70°C to about 200°C at constant frequency of 10 rad/sec. Throughout the experiment the temperature increased by 5°C in steps.
• Table 1 a Gelled within 1-2 min, Shore OO Hardness 32 b. Instant cure at room temp c. No gel for 1 h, seems to thicken in 24hr d. Gelled, Shore OO Hardness 21 in 24hr e. Instant cure at room temp f. No gel for 1 h, seems to thicken in 24hr g. Becomes very thick in 24hr * Molecular Weight
• dimethylphenyl phosphine was very reactive even at low level, i.e. , ⁇ 0.2wt% based on total resin.
• dimethylaminopyridine catalyst provided slower reactivity at similar loading. For this reason, trioctyl phosphine provided best balance of catalytic reactivity, initial latency within the first hour after mixing the two parts and full cure within 24-48 hours.
• the di acrylate resin is separated from the multifunctional thiol resin.
• the mono-acrylate resin can be placed in either Part A or Part B to balance the weight. Based on the density of each part, the weight of each part can be adjusted to ensure the same volume of each part is dispensed through the cartridge and mixed in the mixing area.
• a two-part filled formulation was prepared using alumina as thermally conductive fillers. Details to Sample 8 (#8) are listed in Table 2. This example uses 1:1:1 molar ratio of mono-acrylate : di-acrylate : tri-thiol. A plasticizer was used to balance the weight of Part A & B resin.
• the dispensing rate was measured by a Loctite dual cartridge applicator equipped with 50cc 2K cartridges and a 6.3-21 static mixer under 0.52 MPa for 1 minute to collect the initial dispensing of the composition after purging out a small amount of the inhomogeneous mixture.
• Part A and Part B were dispensed at 1 : 1 ratio (volume) into an aluminium pan. Upon curing for 24 hours at room temperature, a soft composite having Shore OO Hardness of 73 was obtained.
• a combination of two or more di-acrylates with different molecular weight or a combination of a mono- and a di-acrylate in Part A may be adjusted to control the crosslinking density, time to gelation, sample hardness, dispensing rate, etc., of the polysulfide resin.
• Example 3 [0089] In this Sample 9 (#9), a di-acrylate based on polyTHF was used in place of PPG di acrylate. Details to Sample 9 are listed in Table 3. This example uses slight excess of mono acrylate and tri-thiol resins compared to the diacrylate resin to achieve desired hardness and curing speed. Plasticizer was omitted for this sample.
• the dispensing rate was measured by a Loctite dual cartridge applicator equipped with 50cc 2K cartridges and a 6.3-21 static mixer under 0.52 MPa for 1 minute to collect the initial dispensing of the composition after purging out a small amount of the mixture.
• Part A and Part B were dispensed at 1:1 ratio (volume) into an aluminium pan. Upon curing for 48 hours at room temperature, a soft composite having Shore OO Hardness of 75 was obtained.
• Dispensing rate at 30 min showed that Formulation 9 had an extended pot life since the dispensing rate was above zero and did not clog the nozzle, indicating latency desired for thermal interface materials.
• dispensing rate at 30 minutes can be further improved by changing resin stoichiometry, using less catalyst, or moving catalyst to Part A to minimize pre-reaction between the mono-acrylate and the tri-thiol in Part B.
• Sample 9 had acceptable thermal conductivity.
• This example demonstrates a 2-part system using a difunctional thiol and trifunctional acrylate (trimethylolpropane tri-acrylate, TMPTA) in combination with other mono and di-acrylates, as described in Scheme IV.
• Resins in Part A and Part B have equal weights, and Part B was premixed and allowed to stabilize at room temperature for 48 hours before mixing with Part A (Table 4).
• This example demonstrates a 2-part system using a tetrafunctional thiol and difunctional acrylate in combination with a mono-acrylate, as described in Scheme III.
• Resins in Part A and Part B have equal weights, and Part B was premixed and allowed to stabilize at room temperature for 48 hours before mixing with Part A (Table 5). After room temperature cure, there was minimal change after further curing at 100°C for 2 hours, indicating very thorough cure.
• Thermally conductive fillers can be added to this two-part formulation to make gap filler thermal interface materials.

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