High temperature-resistant phase-change thermal interface material based on polyoctenamer

Abstract

The invention relates to high temperature-resistant phase-change thermal interface materials, to a process for producing these materials and to the use thereof.

Description

[0001] High temperature-resistant phase-change thermal interface material based on polyoctenamer

[0002] Field of the invention

[0003] The invention relates to a high temperature-resistant phase-change thermal interface material, to a process for producing this material and to the use thereof.

[0004] Prior art

[0005] WO2022 / 148669 describes a process for producing trans-polyoctenamer-graphene composite material having a high filler content, the highly filled trans-polyalkenamer-graphene composite material itself and the use thereof. The process has the advantage that it is very simple to perform and thus attain a high filler content composite material. In addition, compared to classical plastics and rubber compounding, no high shear forces are required to produce the composite material. Exceptionally high filler contents with good dispersion quality are nevertheless attained. This document provides trans-polyoctenamer- graphene composite materials which have a filler content of graphene material of 15% to 99.9% by weight, wherein the filler content is based on the sum of the mass fractions of trans-polyoctenamer and graphene material which sums to 100% by weight, and a dust number of 0.002% to 1% by weight when the filler content is from 15% to 70% by weight.

[0006] WO2016086410 describes a thermal interface material having a low thermal resistance comprising a polymer, a phase-change material and at least two different thermally conductive fillers which differ in their particle size. The first thermally conductive filler contains aluminium particles having particle sizes between 1 and 25 pm. The second thermally conductive filler contains zinc oxide particles having particle sizes between 0.1 and 3 pm. Titanium adhesion promoters are also employed. The polymer matrix is to be miscible with the thermally conductive fillers and flowable under pressure and heat. Employed to this end are saturated and unsaturated rubber mixtures, especially silicones. The phase-change material employed is selected from waxes, especially paraffins, having melting points between 20°C and 100°C. Polymer waxes having melting points between 40°C and 160°C are also described. The employed solvents are there to solvate the phase-change materials. The mixture is baked and dried at temperatures between 25°C und 170°C. The thickness of the material is between 5 and 80 pm.

[0007] WO2017152353 describes a thermal intermediate material composed of a polymer matrix material, a phase-change material, an amine-based crosslinker and thermally conductive materials. These are especially selected from the group of zinc oxide particles and aluminium particles. The crosslinker is an alkylated melamine resin. The polymer matrix contains ethylene-propylene rubber, silicone rubber, polyethylene / butylene or polyethylene-butylene-styrene material.

[0008] The phase-change materials employed are paraffins having melting points between 20°C and 100°C. Polymer waxes having melting points between 40°C and 160°C are also described. WO2017152353 describes special titanium adhesion promoters. Many semiconductor modules, for example SiC-based semiconductor modules, are operated at higher temperatures than established Si-based modules. This requires that the thermal interface material (TIM) between the module and the heat sink can withstand temperatures above 150°C. This is not the case with established TIM.

[0009] Especially continuous load or cycling at temperatures above 150°C cannot be covered with the known thermal interface materials.

[0010] Problem

[0011] Against the background of the discussed prior art the problem addressed by the present invention was accordingly that of providing a novel high temperature-resistant phase-change thermal interface material. Processes for producing this material should additionally be provided.

[0012] The problem addressed by the present invention was especially that of providing materials with different mechanical properties in order to allow different applications.

[0013] Further problems not explicitly discussed at this point may be derived from the prior art, the description, the claims or the exemplary embodiments.

[0014] Solution

[0015] The problem was solved by providing a high temperature-resistant phase-change thermal interface material containing

[0016] 5 to 30% by weight of component A and 70-95% by weight of component B, wherein component A contains a1) 10-85% by weight of polyoctenamer, a2) 10-85% by weight of polybutadiene, a3) 0.1-5% by weight of stabilizers and component B containing b) thermally conductive fillers, and c) 0-50% by weight of a solvent C, based on the total amount of components A and B.

[0017] The high temperature-resistant phase-change thermal interface material may be provided in the form of a solid if no solvent is employed.

[0018] It has proven advantageous to also provide the high temperature-resistant phase-change thermal interface material in the form of a dispersion by adding a suitable solvent or solvent mixture.

[0019] It is preferable to provide a high temperature-resistant phase-change thermal interface material in the form of a solid containing 5-30% by weight, preferably 15-25% by weight, of component A, wherein component A contains a1) 10-85% by weight, preferably 40-59.9% by weight, of polyoctenamer, a2) 10-85% by weight, preferably 40-59.9% by weight, of polybutadiene, a3) 0.1-5% by weight of stabilizers and

[0020] 70-95% by weight, preferably 75-85% by weight, of component B containing b) thermally conductive fillers, and no solvents.

[0021] In a particularly preferred form the high temperature-resistant phase-change thermal interface materials are provided in a dispersion composed of 5-25% by weight, preferably 10-20% by weight, of component A, wherein component A contains a1) 15-84.9% by weight, preferably 40-59.9% by weight, of polyoctenamer, a2) 15-84.9% by weight, preferably 40-59.9% by weight, of polybutadiene, a3) 0.1-5% by weight of stabilizers and

[0022] 25-90% by weight, preferably 50-60% by weight, of component B containing b) thermally conductive fillers, and c) 5-50% by weight, preferably 20-40% by weight, of a solvent C, based on the total amount of component A and B.

[0023] Thermal resistance is a key parameter for use in the semiconductor industry. Thermal resistance may be adjusted by addition of fillers. The high temperature-resistant phase-change thermal interface material according to the invention contains thermally conductive fillers selected from the group of aluminium, spherical aluminium oxide, graphite, graphene, boron nitride, thickeners or viscosity modifiers, especially (silane-modified) pyrogenic aluminium oxide and mixtures thereof.

[0024] Suitable solvents are required for the production and processing of high temperature-resistant phasechange thermal interface materials. Especially suitable are solvents which dissolve polyoctenamer polybutadiene at room temperature.

[0025] Suitable solvents are selected from the group of non-toxic solvents, especially cyclic ethers, dialkyl ethers, preferably methyltetrahydrofuran, cyclopentyl methyl ether and mixtures thereof.

[0026] The solvents are employed in amounts of 5% by weight to 50% by weight, preferably from 20% by weight to 40% by weight, based on the total amount of component A and component B.

[0027] The high temperature-resistant phase-change thermal interface materials according to the invention contain stabilizers selected from the group of organic phosphites, sterically hindered phenols, thioethers, aromatic amines and mixtures thereof. Combinations of organic phosphites and sterically hindered phenols are preferred. The organic phosphites are preferably selected from the group of tris(2,4-di-tert- butylphenyl)phosphite and distearyl pentaerythritol diphosphite. The sterically hindered phenols are particularly preferably octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. The stabilizers are generally used in amounts of 0.5% by weight to 5% by weight, preferably of 0.6% by weight to 2% by weight, based on component A.

[0028] It has surprisingly been found that the high temperature-resistant phase-change thermal interface materials according to the invention exhibit thermal stability above 150°C.

[0029] A particularly important parameter for the high temperature-resistant phase-change thermal interface materials is viscosity.

[0030] In this context it is necessary to distinguish between two types of viscosity:

[0031] A) printable dispersions must have a viscosity that is high enough to prevent melting of the printed image but low enough to be printed. Shear-thinning behaviour is preferred.

[0032] Preferred viscosity ranges at defined shear rates at room temperature:

[0033] At a shear rate of 0.1 Hz: 500 - 200000 Pa*s

[0034] At a shear rate of 1 Hz: 100 - 20000 Pa*s

[0035] At a shear rate of 10 Hz: 50 - 5000 Pa*s

[0036] The viscosity is adjustable not only via the presence and / or the amount and type of the employed solvent and the fillers. The molecular weight of the polymers also plays a decisive role.

[0037] After the printing process the material is dried to remove the solvent, thus ensuring the material is dry-to- touch at room temperature and the printed image no longer smears. This allows printed components to be readily stored. The drying or baking is performed at temperatures of 20°C - 170°C for 1 to 24 h.

[0038] B) If the high-temperature resistant phase-change thermal interface materials according to the invention are in the form of a solid, for example the printed and dried material obtained after the printing of the printable dispersion, or after the extrusion of the solvent-free mixture, the viscosity must be low enough to ensure that in the liquid state above the melting point of 55°C the material flows into and wets all unevennesses in the surface but also high enough to ensure that it does not flow out from between the heat sink and the heating element.

[0039] Preferred viscosity ranges at defined shear rates at 70°C:

[0040] At a shear rate of 0.1 Hz: 500 - 2000000 Pa*s

[0041] At a shear rate of 1 Hz: 100 - 200000 Pa*s

[0042] At a shear rate of 10 Hz: 50 - 50000 Pa*s It has further surprisingly been found that the high temperature-resistant phase-change thermal interface materials have better mechanical properties in the cold state. The materials are not brittle but rather elastic and have a relatively high tensile modulus.

[0043] It was further found that during reworking, the reapplication of conductive materials to the heating element, the material may be peeled off as a film in contrast to the prior art which breaks down into smaller pieces.

[0044] The demands on the mechanical properties of the high temperature-resistant phase-change thermal interface materials according to the invention are wide ranging. Printable dispersions but also films are preferred for use for the thermal protection management of semiconductor modules, especially of SiC- based, or GaN-based semiconductor modules.

[0045] It is therefore necessary for the viscosity of the melt to be adjustable to the prevent the material from flowing out. The high temperature-resistant phase-change thermal interface material meets this requirement.

[0046] The viscosity of the molten solid is adjusted such that after printing on the SiC-based or GaN-based semiconductor modules the materials according to the invention do not flow in the dry or melted state even in high temperature applications, i.e. pump-out is avoided.

[0047] It is preferable when viscosity adjustment is effected via the ratio of polyoctenamer to polybutadiene.

[0048] A further preferred application in the thermal protection management of semiconductor modules, especially of SiC-based or GaN-based semiconductor modules, is films. The high temperature-resistant phase-change thermal interface material according to the invention can meet this requirement too. The material is processed into pellet material or directly into films without solvent. It may be applied as a self- supporting film, without a substrate film, which is made possible by the mechanical properties.

[0049] For the solid, melt viscosity adjustment is preferably effected via the ratio of polyoctenamer to polybutadiene. An elevated content of polybutadiene reduces the melt viscosity. Viscosity can be increased via the type and amount of the filler content.

[0050] Especially in the printing process the change in viscosity through shear is important.

[0051] It has been found that high temperature-resistant phase-change thermal interface materials are particularly suitable when the trans-polyoctenamer having a molecular weight Mw between 100 000 g / mol and 180 000 g / mol, preferably between 135 000 g / mol and 145 000 g / mol, is employed.

[0052] A polybutadiene having a molecular weight Mnbetween 1000 and 6000, preferably between 2000 and 4000, is also particularly suitable.

[0053] Mw stands for weight-average molecular weight and Mn stands for number-average molecular weight. Determination of molar weight (Mw) mass agent of Polyoctenamer 8012 by gel permeation chromatography (GPC).

[0054] Sample preparation: The sample was dissolved at a concentration of c = 5 g / L in tetra hydrofuran at room temperature. The solutions of the samples were colorless and clear. The sample solutions contained insoluble portions and were filtered into the GPC system prior to injection.

[0055] Column combination: 1 x 3 cm, 3 pm, 100 A (styrene-divinylbenzene copolymer) and 1 x 25 cm, 3 pm, linear, (styrene-divinylbenzene copolymer)

[0056] Mobile phase: tetra hydrofuran pure, stabilized

[0057] Flow rate: 1 ml / min

[0058] Detection: Refractive index

[0059] Calibration and evaluation: A calibration curve was created with polystyrene standards. Due to the method of calibration, the determined molar mass distribution is therefore not absolute molar masses, but polystyrene-equivalent molar masses. The mass mean of the molar weight (Mw) is determined from the molar mass distribution.

[0060] Determination of numerical means of the molar gravity (Mn) of polybutadiene by gel permeation chromatography (GPC).

[0061] Sample preparation: The sample was dissolved at a concentration of c = 5 g / L in tetra hydrofuran at room temperature. The solutions of the samples were colorless and clear. The sample solutions contained insoluble portions and were filtered into the GPC system prior to injection.

[0062] Column combination: 1 x 5 cm, 5 pm, 100 A (styrene-divinylbenzene copolymer) and 1 x 30 cm, 5 pm, linear, (styrene-divinylbenzene copolymer)

[0063] Mobile phase: Tetrahydrofuran pure, stabilized

[0064] Flow rate: 1 ml / min

[0065] Detection: Refractive index

[0066] Calibration and evaluation: A calibration curve was created with the GPC / SEC Ready-Cai-Kit "Polystyrene Low" from the company Perfekt Separation Solution. Due to the method of calibration, the determined molar mass distribution is therefore not absolute molar masses, but polystyrene-equivalent molar masses. The numerical mean of the molar weight (Mn) is determined from the molar mass distribution.

[0067] A process for producing high temperature-resistant phase-change thermal interface materials in the form of a solid is characterized in that compounding of polyoctenamer, polybutadiene, stabilizer and filler is carried out at temperatures of 60°C-250°C over 1 min to 120 min in a plasticizing apparatus, preferably an extruder or kneader. Subsequent further processing of the obtained high temperature-resistant phasechange thermal interface material as a strand is carried out with a suitable apparatus to afford a pellet material or powder. After pelletization or milling the obtained material or film precursor, especially in the form of pellet material or powder, may be further processed into films. Alternatively, the material may also be further processed into films directly in an extruder by blown film extrusion or cast film extrusion.

[0068] A process for producing high temperature-resistant phase-change thermal interface materials in the form of a dispersion is characterized in that mixing of polyoctenamer, polybutadiene, stabilizer, filler and solvent is carried out at temperatures of 10°C-50°C over 5 min to 60 min, preferably 10 to 20 min, in a mixer, preferably in a planetary centrifugal mixer. The resulting mixture can be filled into cartridges as a printable dispersion and used for the printing process.

[0069] High temperature-resistant phase-change thermal interface materials are especially used for heat protection management in semiconductor modules, preferably in SiC-based or GaN-based semiconductor modules.

[0070] The inventive high temperature-resistant phase-change thermal interface materials in the form of a solid are used as films in semiconductor modules, preferably in SiC-based or GaN-based semiconductor modules. The inventive high temperature-resistant phase-change thermal interface materials in the form of a dispersion are used as printable dispersions in semiconductor modules, preferably in SiC-based or GaN- based semiconductor modules.

[0071] Working examples

[0072] Materials used

[0073] Polyoctenamer:

[0074] VESTENAMER® 8012; Evonik Germany

[0075] Liquid polybutadiene:

[0076] POLYVEST® 110; Evonik, Germany

[0077] Spherical aluminium oxide with D50 of 2 pm:

[0078] BAK-2; xtra GmbH, Germany

[0079] Silane-modified pyrogenic aluminium oxide BET 75 - 105 m2 / g:

[0080] AEROXIDE® Alu C 805; Evonik, Germany

[0081] Example 1 : General procedure for compounding moulding materials

[0082] The moulding materials were produced in a co-rotating twin-screw extruder or co-kneader. The pellet material components were metered in via the main intake and the liquid and pulverulent components were metered into the melt at a downstream position. The moulding material composition in % by weight and the most important process parameters are reported in table 1 . Pelletization was by strand pelletization with subsequent drying in a dry air drying cabinet for 12 hours at 40°C.

[0083] The pellet material may then optionally be processed in a film extrusion line to produce films having a thickness of 100 pm to 400 pm. The material exhibits thermal stability at temperatures of 170°C for 1000 h.

[0084] Table 1

[0085] Barrel temperature: 210°C

[0086] Example 2: Production of a pasty dispersion The pasty dispersion was produced using a centrifugal planetary mixer.

[0087] 56 g of cyclopentyl methyl ether, 12 g of polyoctenamer with Mw of 140 000 g / mol (VESTENAMER® 8012), 12 g of liquid polybutadiene with Mn of 2600 (POLYVEST® 110), 0.3 g of distearyl pentaerythritol diphosphite, 96 g of spherical aluminium oxide D50 = 2 pm (BAK-2) and 3.5 g of silane-modified pyrogenic aluminium oxide BET 75 - 105 m2 / g, (AEROXIDE® Alu C 805) 805) are added to the mixing vessel of the centrifugal planetary mixer.

[0088] The mixing operation is then performed for 15 minutes at room temperature. After termination of the mixing operation the dispersion is subjected to a visual inspection to confirm homogeneity. The finished homogeneous dispersion has a pasty consistency and may be used in the stencil printing process. The printed dried material exhibits thermal stability at temperatures of about 170°C for 1000 h.

Claims

Claims1 . High temperature-resistant phase-change thermal interface materials in the form of a solid or a dispersion containing5 to 30% by weight of component A and 70-95% by weight of component B, wherein component A contains a1) 10-85% by weight of polyoctenamer, a2) 10-85% by weight of polybutadiene, a3) 0.1-5% by weight of stabilizers and component B containing b) thermally conductive fillers, and c) 0-50% by weight of a solvent C, based on the total amount of components A and B.

2. High temperature-resistant phase-change thermal interface materials in the form of a solid according to Claim 1 containing5 to 30% by weight of component A, wherein component A contains a1) 10-85% by weight of polyoctenamer, a2) 10-85% by weight of polybutadiene, a3) 0.1-5% by weight of stabilizers and70-95% by weight of component B containing b) thermally conductive fillers, and c) 0% by weight of a solvent C, based on the total amount of components A and B.

3. High temperature-resistant phase-change thermal interface materials in the form of a solid according to Claim 1 containing15 to 25% by weight of component A, wherein component A contains a1) 40-59.9% by weight of polyoctenamer, a2) 40-59.9% by weight of polybutadiene, a3) 0.1-5% by weight of stabilizers and75-85% by weight of component B contains b) thermally conductive fillers, and c) 0% by weight of a solvent C, based on the total amount of components A and B.

4. High temperature-resistant phase-change thermal interface materials in the form of a dispersion according to Claim 1 containing5 to 25% by weight of component A, wherein component A contains a1) 15-84.9% by weight of polyoctenamer, a2) 15-84.9% by weight of polybutadiene, a3) 0.1-5% by weight of stabilizers and25-90% by weight of component B containing b) thermally conductive fillers, and c) 5-50% by weight of a solvent C, based on the total amount of components A and B.

5. High temperature-resistant phase-change thermal interface materials according to Claim 1 containing10 to 20% by weight of component A, wherein component A contains a1) 40-59.9% by weight of polyoctenamer, a2) 40-59.9% by weight of polybutadiene, a3) 0.1-5% by weight of stabilizers and50-60% by weight of component B, wherein component B contains b) thermally conductive fillers, and c) 20-40% by weight of a solvent C, based on the total amount of components A and B.

6. High temperature-resistant phase-change thermal interface materials according to Claim 1 containing thermally conductive fillers selected from the group of aluminium, spherical aluminium, aluminium oxide, spherical aluminium oxide, graphite, graphene and boron nitride, viscosity modifiers and mixtures thereof.

7. High temperature-resistant phase-change thermal interface materials according to Claim 1 containing stabilizers selected from the group of organic phosphites, sterically hindered phenols, thioethers, aromatic amines and mixtures thereof.

8. High temperature-resistant phase-change thermal interface materials according to Claim 1 containing solvents selected from the group of cyclic ethers, dialkyl ethers, preferably methyltetrahydrofuran, cyclopentyl methyl ether and mixtures thereof.

9. High temperature-resistant phase-change thermal interface materials according to Claim 1 containing polyoctenamer having a molecular weight Mw, determined by gel permeationchromatography, between 100 000 g / mol and 180 000 g / mol, preferably between 135 000 g / mol and 145 000 g / mol.

10. High temperature-resistant phase-change thermal interface materials according to Claim 1 containing polybutadiene having a molecular weight Mn, determined by gel permeation chromatography, between 1000 and 6000, preferably between 2000 and 4000.

11. Process for producing high temperature-resistant phase-change thermal interface materials in the form of a solid according to Claim 1 , characterized in that- compounding of polyoctenamer, polybutadiene, stabilizer and filler is carried out at temperatures of 60°C-250°C over 1 min to 120 min in a plasticizing apparatus, preferably in an extruder, and- subsequent further processing of the obtained high temperature-resistant phase-change thermal interface material as a strand is carried out with subsequent pelletization to afford a pellet material or direct extrusion to afford a film.

12. Process for producing high temperature-resistant phase-change thermal interface materials in the form of a dispersion according to Claim 1 , characterized in that- mixing of polyoctenamer, polybutadiene, stabilizer, filler and solvent is carried out at temperatures of 10°C-50°C over 5 min to 60 min in a mixer, preferably in a planetary centrifugal mixer, and a high-temperature-resistant phase-change thermal interface material is isolated in the form of a printable dispersion.

13. Use of high temperature-resistant phase-change thermal interface materials according to Claim 1 , produced according to Claim 11 for producing a film.

14. Use of high temperature-resistant phase-change thermal interface materials according to Claim 1 , produced according to Claim 12 for producing a printable dispersion.

15. Use of high temperature-resistant phase-change thermal interface materials according to Claim 1 for heat protection management of semiconductor modules, preferably of SiC-based or GaN- based semiconductor modules.

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