Thermal interface material with low melting alloy

• US 7,147,367 B2
• Filed: 06/11/2002
• Issued: 12/12/2006
• Est. Priority Date: 06/11/2002
• Status: Expired due to Fees

• Current Assignee: Saint-Gobain Performance Plastics Corporation (Compagnie De Saint-Gobain)
• Original Assignee: Saint-Gobain Performance Plastics Corporation (Compagnie De Saint-Gobain)
• Inventors: Balian, Charles, Currier, Gregg C., Bergerson, Steven E.
• Primary Examiner(s): VERBITSKY, GAIL KAPLAN
• Application Number:
  US10/166,667
• Publication Number:
  US 20030227959A1
• Time in Patent Office: 1,645 Days
• Field of Search: 374/160, 374/159, 374/165, 374/43, 524/404, 524/277, 428/261, 428/348, 428/349, 428/354, 428/355.R, 428/402, 428/403, 428/407, 428/920, 165/185
• US Class Current: 374/44
• CPC Class Codes: H01L 23/3736 Metallic materials H01L23/3732, H01L23/3733, H01L23/3735, H01L23/3737, H01L23/3738 take precedence
• CPC Class Codes: H01L 23/3737 Organic materials with or without a thermoconductive filler
• CPC Class Codes: H01L 23/42 Fillings or auxiliary members in containers or encapsulations selected or arranged to facilitate heating or cooling
• CPC Class Codes: H01L 23/4275 by melting or evaporation of solids
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10T 428/2852 Adhesive compositions

Abstract

A thermal interface composition undergoes a viscoelastic change at microprocessor operating temperatures to transfer heat generated by a heat source, such as a microprocessor to a heat sink. The composition includes a low melting alloy dispersed in a matrix. The matrix comprises a viscoelastic composition which softens at about the operating temperature of the heat source. The viscoelastic composition may include a thermoplastic elastomer, a compatible hydrocarbon oil, and a tackifying resin. In use, the thermal interface composition flows under pressure between the heat source and the heat sink to make thermal contact between the two. When the heat source is operated and reaches operating temperature, the viscoelastic composition softens and the low melting alloy melts at around the operating temperature to form a highly thermally conductive, generally homogeneous mixture which readily transfers heat to the heat sink.

Claims

1. A thermal interface composition for transferring heat between a microprocessor and a heat sink, comprising:

a matrix material which softens at a temperature of about the operating temperature of the microprocessor; and

a low melting alloy in the form of a dispersion in the matrix material substantially free of agglomerated particles, the low melting alloy melting below said temperature at which the matrix material softens, the low melting alloy being a solid at ambient temperature.

2. The thermal interface composition of claim 1, wherein the low melting alloy is a solid at ambient temperature.

12. The thermal interface composition of claim 1, further including:

a thermally conductive filler dispersed within the matrix material.

13. The thermal interface composition of claim 12, wherein the thermally conductive filler is selected from the group consisting of born nitride, aluminum oxide, aluminum nitride, magnesium oxide, zinc oxide, beryllium oxide, silicon carbide, nickel powder, copper flakes, graphite powder, powdered diamond, and mixtures thereof.

14. The thermal interface composition of claim 1, wherein the low melting alloy includes an element selected from the group consisting of bismuth, indium, tin, antimony, and combinations thereof.

15. The thermal interface composition of claim 14, wherein the low melting alloy includes bismuth, indium, and tin.

16. The thermal interface composition of claim 15, wherein the low melting alloy includes bismuth, indium, and tin in a ratio of 10–

50% bismuth, 2–

30% tin, and 30–

80% indium.

17. The thermal interface composition of claim 1, wherein a weight ratio of the matrix material to the low melting alloy is from 1:

1 to 1;

20.

18. The thermal interface composition of claim 1, wherein a weight ratio of the matrix material to the low melting alloy is from 1:

1 to 1;

10.

3. A thermal interface composition for transferring heat between a microprocessor and a heat sink, comprising:

a matrix material which softens at a temperature of about the operating temperature of the microprocessor, the matrix material including a viscoelastic material which undergoes a viscoelastic change at microprocessor operating temperatures; and

a low melting alloy in the form of a dispersion in the matrix material substantially free of agglomerated particles, the low melting alloy melting below said temperature at which the matrix material softens.

4. A thermal interface composition for transferring heat between a heat source and a heat sink, comprising:

a matrix material which softens at a temperature of about the operating temperature of the heat source, the matrix material including a pressure sensitive adhesive; and

a low melting alloy in the form of a dispersion in the matrix material substantially free of agglomerated particles, the low melting alloy melting below said temperature at which the matrix material softens.

5. The thermal interface composition of claim 4, wherein the matrix material includes:

a thermoplastic elastomer;

a compatible plasticizer; and

a tackifying resin.

6. The thermal interface composition of claim 5, wherein the thermoplastic elastomer includes a styrene-alkylene-styrene triblock copolymer.

7. (The thermal interface composition of claim 6, wherein the styrene-alkylene-styrene triblock copolymer includes an alkylene selected from the group consisting of ethylene, propylene, 1-butene, 2-butene, isobutylene, butadiene, isoprene, and combinations thereof.

8. The thermal interface composition of claim 7, wherein the thermoplastic elastomer is selected from the group consisting of poly (styrene-butadiene-styrene) triblock copolymers;

poly (styrene-ethylene-butylene-styrene) triblock copolymers;

poly (styrene-isoprene-styrene) triblock copolymers; and

combinations thereof.

9. The thermal interface composition of claim 5, wherein the compatible plasticizer includes a hydrocarbon oil selected from the group consisting of mineral oils, synthetic oils, and mixtures thereof.

10. The thermal interface composition of claim 9, wherein the mineral oil is selected from the group consisting of paraffinic oils, naphthenic oils, aromatic oils, and mixtures thereof.

11. The thermal interface composition of claim 5, wherein the tackifying resin is selected from the group consisting of natural rosin, modified rosin, glycerol esters of natural and modified rosins;

pentaerythirtol esters of natural and modified rosins, polyterpene resins, copolymers of natural terpenes, terpolymers of natural terpenes, phenolic-modified terpene resins, aliphatic petroleum hydrocarbon resins, aromatic petroleum hydrocarbons, hydrogenated derivatives of aromatic petroleum hydrocarbons, aliphatic petroleum derived hydrocarbons, aromatic petroleum derived hydrocarbons, hydrogenated derivatives of aliphatic petroleum derived hydrocarbons, hydrogenated derivatives of aromatic petroleum derived hydrocarbons, and mixtures thereof.

19. A method for forming a thermal interface comprising:

combining a matrix material with a low melting alloy to form a thermal interface material of low melting alloy dispersed within the matrix material, including;

mixing the low melting alloy with the matrix material at a sufficient temperature such that the low melting alloy melts and is dispersed in the form of a fine dispersion throughout the matrix material, the low melting alloy being substantially free of agglomerated particles, and

cooling the mixture of low melting alloy and matrix material such that the low melting alloy is dispersed throughout the matrix material as discrete particles;

positioning the thermal interface material between a microprocessor and a heat sink, the matrix material being one which softens and remains soft at a softening temperature around the operating temperature of the microprocessor, the low melting alloy being one which melts below the softening temperature; and

operating the heat source, whereby the low melting alloy melts and combines with the matrix material to form the thermal interface.

20. A method of forming a thermal interface material for transferring heat from a microprocessor device to a heat sink, comprising:

mixing a low melting alloy with a matrix material to disperse the low melting alloy in the form of a dispersion throughout the matrix material substantially free of agglomerated particles, the low melting alloy being one which melts at a temperature of between about 30°

C. and about the operating temperature of the microprocessor device, the matrix material comprising a thermoplastic elastomer and plasticizer which softens at a softening temperature around the operating temperature of the microprocessor device to form a generally homogeneous dispersion with the molten low melting alloy, wherein the low melting alloy melts below the softening temperature.

21. The method of claim 20, further including:

the step of mixing including mixing the low melting alloy with the matrix material at a sufficient temperature such that the low melting alloy melts and is dispersed throughout the matrix material; and

after the step of mixing, cooling the mixture of low melting alloy and matrix material while continuing to mix the mixture such that the low melting alloy is dispersed throughout the matrix material as particles.

22. The method of claim 20, further including:

coating a filler material with the low melting alloy; and

the step of mixing including mixing the filler material coated with the low melting alloy with the matrix material.

23. A thermal interface composition which undergoes a viscoelastic change at microprocessor operating temperatures to transfer heat generated by a heat source to a heat sink, the composition comprising:

(A) a viscoelastic composition which softens and remains soft at a temperature of about the operating temperature of the heat source, the viscoelastic composition comprising;

(1) a thermoplastic elastomer,

(2) a compatible hydrocarbon oil, and

(3) a tackifying resin; and

(B) a thermally conductive material in the form of a dispersion within the viscoelastic composition substantially free of agglomerated particles, the thermally conductive material having a melting point below said temperature at which the viscoelastic composition softens.

24. The composition of claim 23, wherein the thermally conductive material comprises a low melting alloy (LMA) incorporated in dispersion form within the composition.