Thermal interface material for high voltage application

Abstract

The present invention relates to a thermal interface material structure for high voltage application, in particular for high voltage power system and to a method of producing the thermal interface material structure. Further, the present invention relates to an electronic apparatus comprising the thermal interface material structure and to a method of manufacturing the electronic apparatus. The thermal interface material structure, comprises in sequence: a gap filler layer, a thermal pad layer, and an adhesive layer having a first adhesion strength to metal of from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer of at least 10% larger than the first adhesion strength.

Description

[0001] Henkel AG & Co. KGaA Wang / cl

[0002] Thermal Interface Material for High Voltage Application

[0003] Technical Fields

[0004] The present invention relates to a thermal interface material structure for high voltage application, in particular for high voltage power system and to a method of producing the thermal interface material structure. Further, the present invention relates to an electronic apparatus comprising the thermal interface material structure and to a method of manufacturing the electronic apparatus.

[0005] Backgrounds

[0006] Thermal interface materials are used to establish a low resistance interface between electronic components, such as integrated circuit chips, and cooling elements such as integrated heat spreaders or cooling plates.

[0007] For example, US 2003128521 A discloses an electronic package for integrated circuit chip, comprising a heat-generating electronic component, a thermally conductive member, a thermal interface material in heat conducting relation between the electronic component and the thermally conductive member, wherein the thermal interface material includes a polymer matrix and thermally conductive filler, and has a required storage shear modulus and loss shear modulus.

[0008] WO 2020011613 A1 discloses an auxiliary assembly of a motor vehicle (2), in particular an electricmotor refrigerant compressor, comprising a housing, which has an electronics compartment and a further compartment, which are separated from each other pressure-tight by means of a partition. Electronics having a printed circuit board are arranged in the electronics compartment. A heat source is connected to the printed circuit board. The heat source is in mechanical contact with the partition via a thermally conductive gel and a thermally conductive pad. The thermally conductive gel and the thermally conductive pad are connected thermally in series between the heat source and the partition.

[0009] In automotive applications, developments in e-mobility and electronics technologies have placed substantial new demands on TIM materials. One important trend has been an increase in voltages to provide faster charging of electric vehicles. However, higher voltage systems need more physical space to avoid problems such as overvoltage and arcing. For example, capacitors or transistors such as MOSFET require a minimum creepage distance between polarities to avoid arcing. As the voltage is higher, the required distance is longer and in turn the component size is larger, which is unfavourable for the manufacturers.

[0010] On the other hand, the increase in voltage requires new solution to electrically insulate the components and to ensure that this insulation is sufficiently robust to last throughout the lifetime of the vehicle. The solutions are particularly challenging because of the complicated logistics in the automotive supply chain and the need for sustainable handling during assembly, and minimal cost. It is also desirable that the TIM material is repositionable and reworkable to minimize scrap and enable higher levels of quality, that it has high temperature stability without loss in mechanical performance, and that the thermal performance not be compromised throughout the lifetime.

[0011] There is a need for improved thermal management solutions that can meet the reliability and robustness requirements of automotive applications with improved dimensional tolerance and ease of handling.

[0012] Summary of the invention

[0013] According to the first object of the invention, a thermal interface material (TIM) structure is disclosed. The TIM, preferably laminated TIM structure comprising, in sequence: a gap filler layer, a thermal pad layer and an adhesive layer having a first adhesion strength to metal from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer sufficient to avoid delamination or other loss in interfacial strength throughout the service life of the component, such as at least 10% larger than the first adhesion strength.

[0014] Another object relates to an apparatus comprising an electronic component, a heat transfer component, and a thermal interface material structure according to the invention which is disposed between the electronic component and the heat transfer component, wherein the gap filler layer is in contact with the electronic component and the adhesive layer is in contact with the heat transfer component.

[0015] Yet another object of the invention relates to a process for producing a thermal interface material structure comprising applying the first side of an adhesive layer onto the first side of thermal pad layer to form an adhesive coated thermal pad, applying a curable gap filler composition onto the second side of the thermal pad to form a layer at least partially covering the thermal pad, applying the second side of the adhesive layer onto one surface of a heat transfer component, applying the second side of the curable gap filler composition onto an electronic component, and curing the curable gap filler composition, wherein the adhesive layer having a first adhesion strength to metal from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer sufficient to avoid delamination or other loss in interfacial strength throughout the service life of the component, such as at least 10% larger than the first adhesion strength.

[0016] The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular descriptions of exemplary embodiments of the invention as illustrated in the accompanying drawings wherein like reference numbers generally represent like parts of exemplary embodiments of the invention. Brief description of the drawings

[0017] Figure 1 is vertical sectional view of a thermal interface material according to the present invention including a gap filler layer, an adhesive layer and in between a thermal pad layer.

[0018] Figure 2 is a vertical sectional view of typical assembly of an electronic apparatus including an electronic component, a heat transfer component, and in between a thermal interface material structure according to the present invention.

[0019] Detailed description of the invention

[0020] In the following passages the present invention is described in more detail. Each aspect so described may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0021] Unless otherwise defined, all terms used in the disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of the ordinary skill in the art to which this invention belongs to. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0022] As used herein, the singular forms “a”, “an” and “the” include both singular and plural referents unless the context clearly dictates otherwise.

[0023] The terms “comprising”, “comprises” and “comprised of’ as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or process steps.

[0024] The recitation of numerical end points includes all numbers and fractions subsumed within the respective ranges, as well as the recited end points.

[0025] All references cited in the present specification are hereby incorporated by reference in their entirety.

[0026] The disclosed thermal interface material structure comprises as shown in FIG. 1 , in sequence, a gap filler layer 14, a thermal pad layer 13 and an adhesive layer 15 having a first adhesion strength to metal from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer sufficient to avoid delamination or other loss in interfacial strength throughout the service life of the component, such as at least 10% larger than the first adhesion strength. The traditional solution for thermal management with robust electrical insulation has been with thermal pads containing a polymer film, such as polyimide for tear-through resistance. However, thermal pads are pre-cured to a specific thickness and while they are conformable, have limited ability to accommodate variations in gap thickness. Curable gap fillers have been a valuable solution to provide an excellent thermal interface independent of thickness, as the dispensed material can be compressed. However, it is not possible to provide a similar level of robustness for electrical insulation to thermal pads containing a polymer interlayer. The soft and natural tackiness on the thermal pads also limits the pre-assembly methodology for faster, more efficient and sustainable processing and logistics for the manufacturing of electronic apparatus. According to this invention, the technologies of thermal pad, curable gap filler and adhesive are leveraged to provide a robust electrically insulating barrier for high voltage applications that are growing in importance for e-mobility and electronics applications in automobiles with the ease of pre-assembly and re-positioning of electronic components during manufacturing.

[0027] Gap filler layer

[0028] The thermal interface material includes a layer of gap filler in contact with the thermal pad and electronic component. The layer of gap filler may partially or fully cover the thermal pad and / or electronic component, and may be in different geometric shapes, such as straight line, dotted line, curved line, circle, square and combination thereof.

[0029] Thermally conductive materials that are applied as pastes in a liquid state are called gap fillers. There is no limitation to the composition of gap filler as long as it is matched to the requirements of thermal conductivity, thermal contact, electrical insulation properties, maximum operating temperatures in the application such as high voltage electronic apparatus. The gap fillers are usually silicone based as silicone has many attractive properties such as surface wetting, high thermal stability, and physical inertness.

[0030] Silicone based gap filler may be prepared from a curable silicone composition for gap filler comprising a reactive silicone and thermally conductive filler. Examples of reactive silicones are polyorganosiloxane, in particular polydimethylsiloxanes having reactive groups selected from the group consisting of vinyl, epoxy, amino, hydrosilane, hydroxy, (meth)acryloxy, and combination thereof.

[0031] Thermally conductive filler used in the curable silicone composition for gap filler is well known in the art for enhancing the thermal conductivity of a polymer matrix. Examples of thermally conductive fillers useful in the polymer matrices of the present invention include metals or ceramics, and specifically include, for example, alumina, aluminum nitride, aluminum hydroxide, aluminum oxide, boron nitride, zinc nitride, and silicon carbide. The thermally conductive silicone composition of the present disclosure can further comprise other components as needed, as long as such components do not impair the effects of the present invention. Other components that can be optionally added include filler surface treatment agents, crosslinking agent, diluents and plasticizers and reaction inhibitors, but are not limited thereto.

[0032] The filler surface treatment agents typically include silanes or siloxane oligomers having two or more, such as three, hydrolyzable groups. Silanes having two or more, especially three, hydrolyzable groups are also known as silane coupling agents, non-limiting examples of which include octyltrimethoxysilane, undecyltrimethoxysilane and cetyltrimethoxysilane. Siloxane oligomers having two or more, such as three, hydrolyzable groups, typically include siloxane oligomers containing a terminal alkoxy group or a side alkoxy group, wherein the oligomers generally have a degree of polymerization less than 100, for example, less than 80 or less than 50. Treating the thermally conductive filler with a filler surface treatment agent can improve the dispersibility of the thermal conductive fillers in the base silicone polymer. Nonetheless, in view that the filler surface treatment agent residues will impair thermal conductivity and increase production costs, the silicone composition for gap filler of the present disclosure is prepared preferably in the absence of a filler surface treatment agent.

[0033] The diluents and plasticizers herein refer to non-aqueous liquids that can reduce the viscosity and increases the flowability of the material. Non-limiting examples of suitable diluents and plasticizers include dimethyl silicone oils having a viscosity of from 10 to 5,000 mPa s at 25° C., MDT silicone oils having a viscosity of from 15 to 300 mPa s at 25° C., a.oj-dimethoxypolydimethylsiloxane having a viscosity of 5-100 mPa s at 25° C., mineral oils having a viscosity of 10-100 mm2 / s at 25° C., acetone, esters (such as phthalates, dibasic esters, phosphate esters and polyesters), and alkyl aromatic compounds (such as dodecylbenzene). Typically, it is true that diluents and plasticizers can be added to a silicone composition for gap filler to reduce its viscosity at high filler loadings. Nonetheless, in view that the diluents and plasticizers, as it exudes or volatilizes, can easily form air cavities resulting in a decrease in thermal conductivity efficiency, the silicone composition for gap filler of the present disclosure is prepared preferably in the absence of diluents and / or plasticizers.

[0034] The type of the crosslinking agent in the reactive silicone composition for gap filler can be determined according to the molecular structure of reactive silicone, i.e. the polyorganosiloxane, more specifically, the type of the functional group in the reactive silicone. The crosslinking agent is an organohydrogenpolysiloxane, typically including those having an average of at least three Si-H groups per molecule. The position of the Si-H groups is not particularly limited, and they can be present only as side groups, or as both side groups and end groups. The organohydrogenpolysiloxane may have a dynamic viscosity at 25° C. of suitably from 10 to 500 mPa s, for example, from 50 to 300 mPa s. Non-limiting examples of reaction inhibitors include acetylenic compounds (such as 3-methyl-1- butyn-3-ol, 1-ethynyl-1 -cyclohexanol and 3,7,11-trimethyl-dodecyn-3-ol), polyvinyl polysiloxane, amide compounds and maleate compounds. In the hydrosilylation reaction, the vinyl-containing silicone oil reacts with the hydrogen silicone oil very quickly if no reaction inhibitors are added, affecting the pot life of the silicone composition for gap filler.

[0035] In one embodiment of the present disclosure, the reactive silicone composition for gap filler comprises: 100 parts by weight of the polyorganosiloxane; 500 to 1500 parts by weight of a thermally conductive filler, and 20 to 100 parts by weight of a crosslinking agent.

[0036] The reactive silicone compositions for gap filler may be in the form of liquid or paste at 25° C, and are available as either 1 -component (1 K) or 2-component (2K) gap filler compositions. Such gap filler compositions are commercially available under the trade name of Bergquist Gap Filler TGF series from Henkel.

[0037] The 1 K gap filler composition are highly viscous thermally conductive pastes that are initially dispensable, but are sufficiently gel-like to remain in place after dispensing. They can be applied with auto-dispensing equipment or by hand.

[0038] In the case of 2K gap filler composition, the two components of the reactive composition are stored separately and, in the case of large-volume applications in automated production lines, are only mixed in a mixing tube via a lifting and dosing unit immediately before application and dispensed. There, the reactive components polymerizes until it is cured. These dispensing systems are associated with investments. For small-volume applications, manual dispensing is preferred. These materials are suitable for compensating extreme tolerances and gaps in non-planar structures. Pressure is not necessary and does not occur, thus avoiding stress on components. This allows precise positioning (form-in-place) as well as placed curing (cure-in-place). Since no or only minimal pressure is exerted during assembly when applying liquid 1 K or 2K reactive gap filler composition, they are suitable for mechanically sensitive and high voltage electric components such as capacitors or transistors such as MOSFET with the thermal pad in the present application. Since gap fillers completely fill all unevenness and gaps, they enable particularly efficient heat transfer between the electronic component and the thermal pad, and in turn to the heat transfer component, such as a heat sink having an aluminium or copper surface.

[0039] Depending on the requirements of the application, the gap filler layer may have a thickness as small as the minimum bondline associated with the material, which typically ranges from 50 to 200 pm, but may be as low as 20 pm or as high as 300 to 400 pm depending on the component and assembly process, up to as high as 5 mm, with the form stability of the gap filler and orientation of the component during determining the upper limit, and exhibits a thermal conductivity of at least 0.5 W / m*K. Thermal pad layer

[0040] The TIM structure of the present invention also comprises a thermal pad layer. The thermal pad is not composed of metal or at least does not contain a metal surface, and may comprise a polymer matrix and fillers dispensed in the polymer matrix.

[0041] The polymer of the thermal pad may be any polymer known in the art for such an application. For example, the polymer may be a polydimethylsiloxane resin, an epoxy resin, an acrylate resin, an organopolysiloxane resin, a polyimide resin, a fluorocarbon resin, a benzocyclobutene resin, a fluorinated polyallyl ether resin, a polyamide resin, a polyimidoamide resin, a cyanate ester resin, a phenol resol resin, an aromatic polyester resin, a polyphenylene ether resin, a bismaleimide triazine resin, a fluororesin, or combinations thereof. Blends of polymers may also be used. The polymer may be a thermoplastic or a thermoset, and may have a low or high molecular weight and Tgdepending on the desired final properties (such a viscosity, modulus, elasticity, etc.). Suitable examples of curable thermoset matrices include acrylate resins, epoxy resins, and polydimethylsiloxane resins, as well as other organo-functionalized polysiloxane resins that can form cross-linking networks via free radical polymerization, atom transfer, radical polymerization ring-opening polymerization, ringopening metathesis polymerization, anionic polymerization, cationic polymerization or any other method known to those skilled in the art. For non-curable polymers, the resulting thermal pad can hold components together during fabrication and provide heat transfer with other layers in the TIM structure during operation of the electronic devices using high voltage.

[0042] As a specific example, the polymer may be a polysiloxane resin, such as an addition curable silicone rubber composition. Such compositions include at least one organopolysiloxane component (such as an organopolysiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule), at least one organohydrogenpolysiloxane, which acts as a crosslinking agent (such as an organohydrogenpolysiloxane containing an average of at least two silicon-bonded hydrogen atoms per molecule), and a hydrosilylation catalyst (such as a ruthenium, rhodium, platinum, or palladium complex), and optionally at least one catalyst inhibitor (used to modify the curing profile and to achieve improved shelf life) and at least one adhesion promoter. Specific types and amounts of each component will be known to one skilled in the art.

[0043] The polymer may further comprise various known additives to achieve the desired overall properties of the thermal pad. For example, the thermal pad may comprise at least one pigment or pigment mixed with a carrier fluid (such as in a pigment masterbatch). Flame retardants can also optionally be used.

[0044] The filler contained in the thermal pad can be any thermally conductive material, including, for example, silica (fumed, precipitated, colloidal, or amorphous), finely divided quartz powder, carbon black, graphite, diamond, a metal (such as silver, gold, aluminum, and copper), silicon carbide, an aluminum hydrate, a metal nitride (such as boron nitride, and aluminum nitrides), a metal oxide (such as alumina, titania, zinc oxide, or iron oxide), or combinations thereof. Preferably the filler has a high conductivity, such as a conductivity of greaterthan or equal to about 10 W / mK, including greaterthan or equal to about 15 W / mK. Thermally conductive fillers that are also minimally electrically conductive are most preferred, and include dielectric materials such as alumina, boron nitride, and aluminum nitride. The filler may further have morphological characteristics that provide additional reinforcement properties to the polymer, and as such would therefore also be considered to be a reinforcing filler in addition to being a thermally conductive filler.

[0045] The filler may also be a treated thermally conductive filler. For example, the filler may be a modified alumina, such as a modified fumed alumina, comprising an alumina, such as a fumed alumina, having attached at least one organic group. Any method known in the art for attaching organic groups to the filler may be used including, for example, chemical reaction of the filler with a surface modification reagent. The choice of organic group will depend on a variety of factors, including, for example, the type of polymer and the reactivity of the filler. It would be expected that, for example, surface treatment of a fumed alumina filler would result in a reduction in viscosity build due to the greater dispersibility of the modified filler in the polymer. This should enable higher loadings of the alumina filler and in turn, lead to higher thermal conductivity of the composite material (without viscosity limitations that would preclude formation of the thermal interface material). Furthermore, a treated thermally conductive filler, such as a modified fumed alumina, would also be expected to have greater compatibility with the polymer, which would be expected to reduce phonon scattering losses as heat is conducted through the filler network and is transferred across the filler / polymer boundaries or interfaces. In addition, improved dispersion of high surface area modified fillers in the polymer would lead to a more effective filler use. For example, a better dispersion increases the probability of particle-to-particle contact and in turn to more efficient and effective thermal percolation networks.

[0046] The relative amounts of the filler and the polymer in the thermal pad can be varied depending on the desired overall properties of the thermal interface material structure. For example, the filler may be dispersed in the polymer in an amount of between about 5% and about 85% by weight based on the total weight of the material, including, for example, between about 10% and about 70% or about 30% and about 60% by weight based on the total weight of the material. The amount of filler will depend, for example, on the type of polymer and the size, morphology, and chemical properties of the filler.

[0047] The thermal pad used in the present application may be reinforced by coating with a reinforcing layer on one or two sides. The reinforcing layer may protect the thermal pad material from moisture impact for longer reliability under harsh environmental conditions. The reinforcing layer is selected from fiberglass, PET, aluminum, polyimide or graphite. Preferably, the thermal pad layer is silicone thermal pad having polyimide as a reinforcing layer on one or both sides. The thermal pads are commercially available under the trade name of Bergquist Sil Pad TSP series and Bergquist Gap Pad TGP series from Henkel.

[0048] The thermal pad layer has a thickness of, for example, 5-400 mil (0.1-100 mm), and preferably about 5 mil (127 pm), for applications requiring excellent heat dissipation, with bulk thermal conductivity of at least 0.5 W / mK according to ASTM D5740 method, with multiple thicknesses used to determine thermal conductivity independent of the contact resistance.

[0049] Adhesive layer

[0050] The thermal interface material structure also includes an adhesive layer to provide adhesion between the thermal pad layer and the heat transfer component such as a heat sink typically having an outer surface of aluminum or copper.

[0051] It has been surprisingly found that when the respective adhesion strength of the adhesive layer to the thermal pad and to the heat transfer component is well selected, the pre-assembly of the adhesive on the thermal pad to form an adhesive coated thermal pad and the re-positioning of the adhesive coated thermal pad onto the heat transfer component can be achieved.

[0052] Specifically, the adhesive layer must exhibit an adhesion strength sufficiently low to allow for removal and repositioning prior subsequent assembly steps, which may include dispensing and compression with the thermal gap filler. It has been surprisingly found that such adhesion performance can be well achieved with a first adhesion strength of the adhesive layerto the metal substrate ofthe heat transfer component, such as stainless steel, aluminium or copper, as commonly measured via a 180° peel- off test on stainless steel according to the ASTM D3330 / D3330M Test Method A, may be, for example, 50 to 1000 g / in, preferably from 50 to 800 g / in, preferably from 75 to 500 g / in, more preferably from 100 to 300 g / in. In addition, the adhesive layer must exhibit a second adhesion strength to the thermal pad layer sufficiently greater than the first adhesion strength, which is at least 10%, or at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 100%, at least 150%, at least 200% largerthan the first adhesion strength.

[0053] In addition, the adhesive layer can be rebonded after being peeled from metal. The first adhesion strength of the adhesive layer after peeling for 3 times is preferably at least 50% of the initial first adhesion strength.

[0054] The adhesive layer may contain or be produced from an acrylate or silicone pressure-sensitive adhesive. A silicone pressure-sensitive adhesive having high weather resistance is preferably used. As used herein, the term “pressure-sensitive adhesive” or “PSA” refers to a viscoelastic material that possesses the following properties: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized by being normally tacky at room temperature. Materials that are merely sticky or adhere to a surface do not constitute a PSA; the term PSA encompasses materials with additional viscoelastic properties. PSAs are adhesives that satisfy the Dahlquist criteria for tackiness, which means that the shear storage modulus is typically 3x105Pa (300 kPa) or less when measured at 25° C. and 1 Hertz (6.28 radians / second). PSAs typically exhibit adhesion, cohesion, compliance, and elasticity at room temperature.

[0055] Examples of the silicone pressure-sensitive adhesive include a peroxide cure type silicone pressuresensitive adhesive and an addition cure type silicone pressure-sensitive adhesive. Specific examples of the silicone pressure-sensitive adhesive include a silicone pressure-sensitive adhesive obtained from a material containing a silicone gum and a silicone resin. For example, an organopolysiloxane containing dimethylsiloxane as a main structural unit can be used as the silicone gum. For example, an MQ resin containing an M unit of RsSiOw and a Q unit of SiOa can be used as the silicone resin.

[0056] The silicone pressure-sensitive adhesive may contain thermal conductive filler to improve the thermal conductivity for the application in high voltage electronic apparatus. The filler may also be a treated thermally conductive filler such as a modified fumed aluminum or a calcined aluminum oxide comprising >95%, >97%, or >98% AI2O3.

[0057] The relative amounts of the filler and the polymer in the silicone PSA can be varied depending on the desired overall properties of the thermal interface material structure. For example, the filler may be dispersed in the polymer in an amount of between about 5% and about 80% by weight based on the total weight of the material, including, for example, between about 10% and about 70% or about 30% and about 60% by weight based on the total weight of the material. The amount of filler will depend, for example, on the type of polymer and the size, morphology, and chemical properties of the filler.

[0058] The silicone PSAs are commercially available under the trade name of SilGrip series from Momentive.

[0059] The adhesive layer has a thickness of, for example, 30 to 70 pm, and preferably about 50 pm, and exhibits a thermal conductivity of at least 0.5 W / m*K.

[0060] Another aspect of the invention relates to an electronic apparatus 10 as shown in FIG. 2 comprising an electronic component 11 , a heat transfer component 12, and a thermal interface material structure including a gap filler layer 14, a thermal pad layer 13, and an adhesive layer 15 according to the invention which is disposed between the electronic component 11 and the heat transfer component 12, wherein the gap filler layer 14 is in contact with the electronic component 11 , such as a high voltage device, and the adhesive layer 15 is in contact with the heat transfer component 12. Nonlimiting examples of the electronic component 11 can include insulated gate bipolar transistors (IGBT), metal oxide semiconductor field effect transistors (MOSFET), diodes, metal semiconductor field effect transistors (MESFET), and high electron mobility transistors (HEMT) used for applications not limited to avionics applications, automotive applications, orthe like. In one preferred embodiment, the electronic component 11 is a MOSFET. The heat transfer component 12 can be of any suitable type or configuration, such as a heat spreader, a heat sink, or any other type of heat transfer component of a thermal solution for an electronic device. In one preferred embodiment, the heat transfer component 12 is a heat sink, more preferably a heat sink having at least one surface of aluminum or copper. In view of the selected adhesive layer, the electronic apparatus 10 is peelable and re-bondable from the interface of the adhesive layer and heat transfer component for at least once, and preferably at least twice.

[0061] Yet another aspect of the invention relates to a process for producing a thermal interface material structure comprising applying the first side of an adhesive layer onto the first side of thermal pad layer to form an adhesive coated thermal pad, applying a curable gap filler composition onto the second side of the thermal pad to form a layer at least partially covering the thermal pad, applying the second side of the adhesive layer onto one surface of a heat transfer component, applying the second side of the curable gap filler composition onto an electronic component, and curing the curable gap filler composition, wherein the adhesive layer has a first adhesion strength to metal from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer sufficient to avoid delamination or other loss in interfacial strength throughout the service life of the component, such as at least 10% larger than the first adhesion strength.

[0062] Optionally, before applying onto one surface of a heat transfer component, the second side the adhesive layer is laminated with a release liner, preferably a PET release liner. Preferably, the adhesion layer has an adhesion strength to the release liner of less than 50 g / in, in particular less than 20 g / in measured according to ASTM D3330 / D3330M Method D for ease of handling.

[0063] The curable gap filler cures under 25° C or under an elevated temperature such as 60° C or 80° C assisted with an external heating device.

[0064] EXAMPLES

[0065] Preparation and test of thermal interface material and the electronic apparatus

[0066] An adhesive layer based on a silicone adhesive commercially available under the trade name of SilGrip from Momentive was provided. The adhesive layer was coated on a roll consisting of a silicone thermal pad commercially available underthe trade name of TSP K1300 from Henkel having a thickness of 150 micrometer to a coated thickness of 25 micrometer and laminated with a PET release liner with a thickness of 75 micrometer. The silicone thermal pad is a laminate of silicone layer and a reinforcing layer composed of polyimide.

[0067] The adhesive layer has a first adhesion strength to metal of 200 g / in, measured according to ASTM D3330 / D3330M Method A and has a second adhesion strength to the silicone based thermal pad layer of at least 50% larger than the first adhesion strength and an adhesion strength to the release liner of 20 g / in or less according to ASTM D 3330 or D3330M Method D.

[0068] After the release liner was removed, the adhesive coated silicone pad was attached to a heat sink made of aluminum using finger force. The heat sink could then be moved and repositioned for further assembly, or transported for assembly at a separate location, without movement or loss of contact with the silicone pad. Finger force could then be used to separate the adhesive layer in the electronic apparatus and the adhesive layer could be easily peeled from the heat sink without residue, repositioned and rebonded to the heat sink again for 3 times, while a strong bonding between the adhesive layer and thermal pad still remained. It was found that an adhesion strength below 1000 g / in, preferably below 300 g / in was sufficient to allow for removal and repositioning, and that an adhesion to the release liner less than 20 g / in was adequate to allow for ease of handling.

[0069] After the silicone pad was adhered and repositioned, the other side of the silicone thermal pad was coated with a thin layer of a curable silicone gap filler paste in liquid form at room temperature. The silicone gap filler is commercially available under the trade name of Bergquist TGF 4400LVO from Henkel. A TO-220 transistor, which was selected as a representative electronic component for the assembly with an interfacial contact area of 10.2 x 15.1 mm, was then compressed on the gap filler using a spring clip with a nominal load of about 35 PSI (0.2 MPa) to reach a thickness of about 250 micrometers. The latter was then allowed to cure for 24 hours at room temperature. The electrical insulation of the component was then tested to be >6 kV based on the ASTM D149 using a D149 series AC dielectric breakdown tester from Haefely Hipotronics.

[0070] The suitability of the assembly of the configuration for high voltage applications was evaluated using a modified DC voltage test, where a 500 VDC was applied to a knife side with a ground on a lower platen where the component was applied. The test was run with a load frame at a speed of 0.039 in / min, with a control used to terminate the test once the circuit was completed due to cut-through of the reinforcing layer. The test, which was carried out without the gap filler or adhesive layer as a worst-case example, showed a peak load of 24 lb (107 N) was required on the knife edge to complete the circuit. An equivalent test carried out according to ASTM F1306-21 measured a cut-through resistance of >20 N (4.5 lb), which similarly demonstrates the high robustness of the assembly, with differences in magnitude associated with differences in method, tip geometry, and termination conditions. A further example of the robustness of the base material prior to gap filler addition was carried out via a mandrel test in accordance with IEC 62368-1 5.4.4.6.5, in which the electrical resistance exceeded 5000 V AC for 60 seconds at the tip of the mandrel geometry.

[0071] While this disclosure has been described as having a preferred design, the present disclosure can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.

Claims

Claims1 . A thermal interface material structure, comprising in sequence: a gap filler layer, a thermal pad layer, and an adhesive layer having a first adhesion strength to metal of from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer of at least 10% larger than the first adhesion strength.

2. The thermal interface material structure according to claim 1 , wherein the gap filler layer comprises cured product of a curable gap filler composition.

3. The thermal interface material structure according to claim 2, wherein the curable gap filler composition comprises a reactive silicone and a thermally conductive filler.

4. The thermal interface material structure according to claim 3, wherein the reactive silicone is polyorganosiloxane, in particular polydimethylsiloxanes having reactive groups selected from the group consisting of vinyl, epoxy, amino, hydrosilane, hydroxy, (meth)acryloxy, and combination thereof.

5. The thermal interface material structure according to claim 3, wherein the thermally conductive filler is selected from the alumina, aluminum nitride, aluminum hydroxide, aluminum oxide, boron nitride, zinc nitride, silicon carbide and combination thereof.

6. The thermal interface material structure according to claim 1 , wherein the thermal pad comprises a polymer matrix, preferably silicone, and fillers dispensed in the polymer matrix.

7. The thermal interface material structure according to claim 6, wherein the filler is dispersed in the polymer in an amount of between about 5% and about 80% by weight based on the total weight of the material, including, for example, between about 10% and about 70% or about 30% and about 60% by weight based on the total weight of the material.

8. The thermal interface material structure according to claim 1 , wherein adhesive layer has a first adhesion strength to metal of from 50 to 800 g / in, preferably from 75 to 500 g / in, more preferably from 100 to 300 g / in measured according to ASTM D3330 / D3330M Method A.

9. The thermal interface material structure according to claim 1 , wherein the adhesive layer has a second adhesion strength to the thermal pad layer of at least 20%, preferably at least 50%, more preferably at least 80%, in particular at least 100% largerthan the first adhesion strength.

10. The thermal interface material structure according to claim 1 , wherein the adhesive layer is a layer of silicone or acrylate based pressure-sensitive adhesive.

11. An apparatus comprising an electronic component, a heat transfer component, and a thermal interface material structure according to the invention which is disposed between the electronic component and the heat transfer component, wherein the gap filler layer is in contact with the electronic component and the adhesive layer is in contact with the heat transfer component.

12. The apparatus according to claim 11 , wherein the electronic component is selected from insulated gate bipolar transistors (IGBT), metal oxide semiconductor field effect transistors (MOSFET), diodes, metal semiconductor field effect transistors (MESFET), and high electron mobility transistors (HEMT).

13. The apparatus according to claim 11 , wherein the electronic apparatus is peelable and re- bondable from the interface of the adhesive layer and heat transfer component for at least once, and preferably at least twice.

14. A process for producing a thermal interface material structure comprising applying the first side of an adhesive layer onto the first side of thermal pad layer to form an adhesive coated thermal pad, applying a curable gap filler composition onto the second side of the thermal pad to form a layer at least partially covering the thermal pad, applying the second side of the adhesive layer onto one surface of a heat transfer component, applying the second side of the curable gap filler composition onto an electronic component, and curing the curable gap filler composition, wherein the adhesive layer having a first adhesion strength to metal of from 50 to 1000 g / in, measured according to ASTM D3330 / D3330M Method A and having a second adhesion strength to the thermal pad layer of at least 10% larger than the first adhesion strength.

15. Use of the thermal interface material structure in manufacturing electronic apparatus comprising MOSFET.

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