JPH1142730A - Thermal conductivity interface for electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide interface, which has excellent mechanical, electrical, thermal, and chemical characteristics, and can be assembled in low pressure flow by constructing a laminated sheet having specified outer layers arranged on both sides of a specified base. SOLUTION: Thermal conductivity interface having mechanical adaptability is composed of a laminated sheet having outer layers arranged on both sides of a base, which is selected from a layer group comprising glass fiber, aluminum foil, expanded metal, polyimide, or polyester. The outer layers have construction represented by a formula (R1 is selected from a group composed of a hydrogen, hydroxyl, or methyl group, and x is an integer having 1-1,000 value), and are composed of organosiloxane having approximately 10-10,000 centipoise viscosity, and poly-dimethyl siloxane having, for example, a hydrogenated end. And they are constructed of reactive product composed of a mixture with a dihydryl aliphatic chain extender having approximately 10-10,000 centipoise viscosity. The reactive product is filled with fine particle solid of approximately 10-60% amount in volume, and the rest is the reactive product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the present invention on May 19, 1995.
"Thermal Conductive Interface for Electronic Devices"
No. 08 / 445,048.

The present invention generally relates to a mechanically compliant, thermally conductive interface used to electrically insulate and thermally couple a printed circuit board to a heat sink, metal chassis, or heat spreader. The interface materials of the present invention have very desirable electrical and mechanical properties, and practically all of the materials that require heat to be conducted from the device to the frame, chassis, heat spreader, or other support surface. Can be used to assemble electronic devices.

[0003]

In the past, various mechanically compliant, thermally conductive interface devices have been proposed to insulate electronic devices from heat sinks such as frames, chassis, heat spreaders, and the like. While these interfaces have been fairly useful and quite satisfactory, the formulations of the present invention have very good mechanical properties, good electrical properties, and compatibility with exceptional thermal and chemical properties Offers a number of advantages in terms of These advantages can be benefited by the use of controlled molecular weight silicones and, optionally, by the use of a surface coating of the pressure sensitive adhesive layer. Thus, the thermal interface scheme of the present invention matches the relative positioning of the assembly without harming, sacrificing or otherwise impeding the mechanical, electrical, thermal and chemical properties. Enables assembly by low pressure flow.

[0004]

SUMMARY OF THE INVENTION A thermally conductive interface material of the present invention is a member comprising a highly compliant silicone polymer filled with thermally conductive electrically insulating particulates, such as alumina and boron nitride. including.
The silicone has the following structural formula

Embedded image Wherein R ₁ is selected from the group consisting of hydrogen, hydroxyl or methyl groups, and wherein x represents an integer having a value from 1 to 1000, which is a conventional organosiloxane.

Typically, the material comprises a liquid organosiloxane of the above structure and the following structural formula

Embedded image A chain extender, such as a hydride terminated polydimethylsiloxane material, having the formula wherein R ₂ represents either a hydrogen, methyl or hydroxy group and y represents an integer having a value from 1 to 1000. Produced as a reaction product with

The use of chain extenders of this type for controlling the molecular weight of organosiloxane polymers is, of course, well known. Also, methods and techniques for reacting those materials are well known to those skilled in the art,
And generally comprises mixing the materials and heating to 120 ° C. for about 5 minutes in the presence of a platinum catalyst and a cure inhibitor such as a cyclic vinyl siloxane.

Other types of materials have the formula

Embedded image (Where the molar ratio of x to y can vary from 10% to 100%). Copolymers of hydromethylsiloxane and dimethylsiloxane are known. This type of material acts as a crosslinking agent. Other types of materials include, for example,

Embedded image And trifunctional and tetrafunctional hydrosiloxanes.

[0008] As a suitable carrier for the above-mentioned polymer materials, a layer of glass fibers may be used, again to give a carrier having good mechanical, electrical and thermal properties, And it is well suited for this application. Glass fibers having a density of about 1 to 4 ounces / square yard may be used in carriers having a thickness of preferably 3 mils.

[0009] In practical use, the finished thermally conductive interface material of the present invention preferably has a thickness in the range of 20 mils to 500 mils, and a thickness in this range will result in a substantially overall thickness. It provides the desired overall thermal resistance to allow for efficient use, as well as providing adequate compliance for the interface. Electrical properties, of course,
A thickness near the upper limit is enhanced, but the breakdown voltage of the material is high enough to allow the use of thicknesses up to about 125 mils and beyond. In some applications, materials having thicknesses as low as about 15 mils may be used, and for some other applications, the operating conditions may be about 500
Allows thickness up to the mill.

[0010] Other supports may also be used, including various aluminum foils in thicknesses of 1 mil to 10 mils. For example, a polyimide (amide) film such as Kapton ^™ may be used at a thickness of 1 mil to 3 mils. Polyester films ranging in thickness from 1 mil to 10 mils may also prove useful. The composition may also be injection molded into various shapes, or alternatively, may be pressed into sheets with or without reinforcement.

In some applications, it may be desirable to provide a pressure sensitive adhesive coating on one or both major surfaces.
A pressure-sensitive adhesive consisting essentially of polydimethylsiloxane may suitably be used. In some of these applications,
It may be desirable to utilize a release film to facilitate handling of the thermally conductive interface material prior to actual end use or assembly operations.

[0012] The features of the present invention will be more fully understood from the following specification, appended claims and appended drawings.

[0013]

In accordance with a preferred embodiment of the present invention, the mechanically compliant, thermally conductive interface material or pad uses a fiberglass carrier, and its compliant material disposed on both sides of the carrier. Manufactured by layers of material. The compliant material comprises a compressible or compressible silicone polymer loaded with a specific filler selected from the group consisting of alumina and boron nitride and mixtures thereof. If desired, and for certain applications, a pressure sensitive adhesive may be used on either of the two main surfaces, and the pressure sensitive adhesive may be used for certain applications and The condition may facilitate assembly and manufacture.

EXAMPLES The mechanically compliant, thermally conductive interface material of the present invention can be manufactured according to the specific examples described below.

EXAMPLE 1 Structural formula

Embedded image Wherein R ₁ represents a methyl group, and the material is liquid and has a viscosity of 1000 centipoise. This material is mixed with a dihydrol aliphatic chain extender consisting essentially of hydride terminated polydimethylsiloxane and having a viscosity of 500 centipoise. Such chain extenders are, of course, commercially available.

After mixing the reactants, about 25 ppm of a catalyst consisting essentially of a divinyl adduct of platinic acid was added. The material was placed in a container in which the glass fiber carrier was located in a central position. The mixture was then cured at 150 ° C. for 10 minutes. Glass fiber carrier is 2
It had a density of ounces / square yard and a thickness of 4 mils. A layer of pressure-sensitive adhesive consisting essentially of polydimethylsiloxane was applied to the surface thereon. The adhesive film is compatible with the silicone and bonds to its surface. The composite is then prepared for cutting or other processing that may be required for custom or general use. A release film made of polyethylene is typically used as the lower surface layer and will, of course, stay with the flexible thermally conductive interface for as long as necessary. When completed, the overall thickness of the composite is 80
It was a mill.

Example 2 The organosiloxane of Example 1 was used with a chain extender consisting essentially of hydride terminated polydimethylsiloxane and having a viscosity of 100 centipoise.
The processing conditions were the same as in Example 1, and a mechanically compliant thermally conductive interface material was formed therefrom. This material was filled with a particulate solid consisting essentially of alumina having an average particle size of about 5 microns. The complex is 29
% Alumina by weight, with the balance being polymer. Such materials are, of course, commercially available. The total thickness is 25 mil.

Example 3 Structural formula

Embedded image Wherein R ₁ represents a methyl group, and the material is liquid and has a viscosity of 100 centipoise. This material is mixed with a dihydryl aliphatic chain extender consisting essentially of hydride terminated polydimethylsiloxane. Such chain extenders are, of course, commercially available.

After the reactants have been mixed,
pm of a catalyst consisting essentially of platinum was added and the material was placed in a container in which the central glass fiber carrier was located. The mixture was then cured at 150 ° C. for 10 minutes. The glass fiber carrier had a density of 2 oz / square yard and a thickness of 4 mils. A layer of pressure-sensitive adhesive consisting essentially of polydimethylsiloxane was applied to the surface thereon. The adhesive film is compatible with the silicone and bonds to its surface. The composite is then prepared for cutting or other processing that may be required for custom or general use. A release film composed of polyethylene is typically used as the lower surface layer,
And, of course, will stay with the flexible thermal interface as needed. When completed, the overall thickness of the composite was 125 mils.

EXAMPLE 4 Structural formula

Embedded image A relatively high molecular weight organosiloxane is selected, wherein R ₁ represents a methyl group, and the material is liquid and has a viscosity of 500 centipoise. This material is mixed with a dihydroxy aliphatic chain extender consisting essentially of hydride terminated polydimethylsiloxane. Such chain extenders are, of course, commercially available.

After the reactants have been mixed,
pm of a catalyst consisting essentially of platinum was added and the material was placed in a container in which the central glass fiber carrier was located. The mixture was then cured at 150 ° C. for 10 minutes. The glass fiber carrier had a density of 2 ounces per square yard and a thickness of 80 mils. A layer of pressure-sensitive adhesive consisting essentially of polydimethylsiloxane was applied to the surface thereon. The adhesive film is compatible with the silicone and bonds to its surface. The composite is then prepared for cutting or other processing that may be required for custom or general use. A release film of polypropylene is typically used as the bottom layer and will, of course, remain with its conformable thermally conductive interface if desired.

EXAMPLE 5 Structural formula

Embedded image And a relatively low molecular weight organosiloxane wherein R ₁ represents a methyl group, and the material is liquid and has a viscosity of 10 centipoise. This material is mixed with a dihydroxy aliphatic chain extender consisting essentially of hydride terminated polydimethylsiloxane. Such chain extenders are, of course, commercially available.

After the reactants have been mixed,
pm of a catalyst consisting essentially of platinum was added and the material was placed in a container in which the central glass fiber carrier was located. The mixture was then cured at 150 ° C. for 10 minutes. The glass fiber carrier had a density of 2 ounces per square yard and a thickness of 40 mils. A layer of pressure-sensitive adhesive consisting essentially of polydimethylsiloxane was applied to the surface thereon. The adhesive film is compatible with the silicone and bonds to its surface. The composite is then prepared for cutting or other processing that may be required for custom or general use. A release film of polyethylene is typically used as the lower surface layer and will, of course, remain with its conformable thermally conductive interface if desired.

Representative Properties of the Finished Product As noted above, the mechanically compliant, thermally conductive interface material of the present invention has been found to have excellent mechanical, electrical, thermal and chemical properties. Was. An example of compression versus applied force is shown in FIG. 3, where this curve illustrates the desired and predictable compression exerted by the various applied loading forces. With respect to other properties, Tables I, II and III appear to be important. These tables are shown below.

[0025]

TABLE I Representative electrical properties Breakdown voltage: thickness (inches) volts AC test method 0.20 7000 ASTM D-149 0.050 10,000 ASTM D-149 0.060 12000 ASTM D-149 0.080 20,000 or more ASTM D-149 0.125 20,000 or more ASTM D-149

[0026]

TABLE II Representative Mechanical Properties Thickness 0.020 "-0.500" ASTM D-374 Color Pink Visual Compression Coefficient 300 PSI ASTM D-1621 Compression Deflection 10% 30 PSI ASTM D-575 50% 200 PSI ASTM D-575 Compression set 65%

[0027]

TABLE III Thermal properties (typically using interface of Example 1, thickness 80 mils) Thermal resistance Thermal resistance (° C / W) Thickness (ASTM D-54P) Pressure (psi) (up to -220 ) ) (Mill) (° C-in ² / W) 256 20 0.46 50 5 30 0.70 100 4 40 0.93 200 350 50 1.16 60 1.39 80 1.85 125 2.90

It is noted that other forms of the interfaces of the present invention may be used and manufactured, and that other techniques may be utilized for their preparation as well.
Of course, it will be understood.

EXAMPLE 6 An interface manufactured according to Example 1 was coated with a surface layer of a pressure-sensitive adhesive consisting of polydimethylsiloxane.
The layer of pressure-sensitive adhesive had a thickness of 1 mil. This material was compatible with the silicone and bonded well to it. When a pressure sensitive adhesive layer is used, a second release film may be used, or alternatively, the material may be packaged in a roll.

Turning now to FIGS. 4A to 4E,
FIG. 4A depicts the isobar of viscosity achieved by a change in formulation. Inspection of FIG. 4A demonstrates the dramatic effect of the addition of 100 centipoise. FIG. 4C shows the significant effect of low viscosity divinyl silicone on the hardness properties of the final product.

EXAMPLE 7 A composite mixture design experiment was undertaken to determine the effect of various reactants on the properties of the reaction product. The reaction product was mixed with alumina such that the alumina content in each case was as follows: Alumina (average particle size, 5 microns) = 71% by weight Polymer component = 29% by weight (a) 1000 cps divinyl silicone (x ₁ ) = 1
-100 mol% (b) 100 cps divinyl silicone (x ₂ ) = 0
100 mol% (c) 500 cps divinyl silicone (x ₃ ) = 0
100 mol% These reactants were mixed and processed according to the conditions described in Example 1 without the presence of glass fibers.

A design matrix was created and the results were analyzed by computer. FIG.
The properties described in 4E are as follows. (A) Centipoise viscosity (FIG. 4A) (b) 10% compression force (force required to achieve 10% compression of initial thickness) (ASTM-D-575) (FIG. 4)
B) (c) 50% compression force (force required to achieve 50% compression of initial thickness) (ASTM-D-575) (FIG. 4)
B) (d) Percentage of solvent absorption (24 hours) (FIG. 4D) and (e) Compression set (ASTM-D-395) (FIG. 4)
E)

Example 8 Each reactant of Example 2 was used to prepare a reaction product.
At that time, the reaction product was filled with fine graphite particles. The material contained 50% by weight of graphite, with the balance being polymer.
A material having excellent thermal properties with an overall thickness of 25 mils was obtained.

General Assembly Configuration Turning now to FIGS. 5 and 6, the entire electronic device 20 shown generally is a base having a circuit array 22 in the form of electrical and electronic components disposed thereon. Or it includes a chassis member. Circuit components typically include solid-state active components, such as transistors, microchips, etc., as in 23-23. Array 22 also includes a number of passive portions, such as illustrated in 24-24, in the form of resistors, capacitors, etc., all of which are disposed on substrate 25. The entire assembly is housed in shroud member 26, where shroud 26 cooperates with chassis 21 to form a complete enclosure. A generally shown mechanically compliant, thermally conductive interface member 27 is inserted between the upper surface of both the chassis 21 and the circuit array 22 and the inner surface 28 opposite the shroud 26.

Turning now also to FIG. 6, the portion of the compliant, thermally conductive interface pad 27 that contacts the circuit component deforms and flows from its planar or rectangular shape, thereby causing it to flow. The individual circuit components are wrapped and housed in cavities formed therein.
In FIG. 6, two microchips 2 on a circuit board 25
3-23 are illustrated as compliant thermal conductive interfaces and their combination that flow to conform to the shape required by the components to achieve the illustrated results. Because of the highly desirable flow properties of the formulation of the present invention, the compliant heat conductive interface pad 27
Will deform under very low pressure and will not interrupt, destroy, or otherwise interfere with the integrity of the individual circuit component leads and other elaborate parts.

To increase the heat dissipation from the assembly, thermally conductive layers are illustrated at 28 and 30, where these layers enhance their work.

As can be seen from these figures, the mechanically compliant, thermally conductive interface possesses the physical properties such that the flexible material comprising the interface flows to form a natural cavity therein. I do. The low durometer of the product allows the interface member to conform to the irregular surfaces of the circuit assembly. About 10 psi due to its low durometer hardness
Moderately low pressures are typically all that is required to achieve the above results.

It will, of course, be understood that various partial modifications may be made to the specific examples provided above without departing from the spirit and scope of the invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view taken through an assembly using a compliant, thermally conductive interface made in accordance with the present invention.

FIG. 2 is a perspective view showing the shape of an interface device manufactured according to the present invention, which is made to order;

FIG. 3 is a graph showing percent compression versus applied force for a compliant thermally conductive interface made in accordance with the present invention.

4A to 4E each show a viscosity (FIG.
A), the force required to achieve 10% compression of the initial thickness (FIG. 4B), the force required to achieve 50% compression of the initial thickness (FIG. 4C), solvent absorption 5 is a graph of the composition showing the response (FIG. 4D) and the isobar of the compression set (FIG. 4E).

FIG. 5 is a perspective view, in the form of an exploded assembly, illustrating a representative assembly using the interface material of the present invention as a component of the assembly.

FIG. 6 is a vertical cross-sectional view taken through the assembly illustrated in FIG. 5, showing that the interface material is compatible with the component containing the circuit assembly.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 23/36 G06F 1/00 360C // B32B 27/00 101 H01L 23/36 D

Claims (13)

[Claims] A mechanically compliant, thermally conductive interface inserted between a heat sink and an electronic device for use as a mounting barrier in combination with the electronic device, comprising: (a) a support and its support; Comprising a laminate having outer layers disposed on both sides of a support, wherein the support is selected from the group consisting of layers of glass fiber, aluminum foil, copper foil, expanded metal, polyimide (amide), and polyester; And (b) the outer layer has the structural formula Wherein R ₁ is selected from the group consisting of hydrogen, hydroxyl or methyl groups, and x represents an integer having a value of 1 to 1000, and having a viscosity of about 10 to 10,000 centipoise. Siloxane and structural formula Wherein R ₂ is selected from the group consisting of hydrogen, methyl and hydroxy groups, and y represents an integer having a value of 1 to 1000, and having a viscosity of about 10 to 10,000 centipoise. Comprising a reaction product of a mixture with an extender, and wherein the organosiloxane reaction product is packed with a particulate solid in an amount of about 10% to 60% by volume, with the remainder being the reaction product. The interface as recited above. 2. The particulate solid is alumina, boron nitride,
The mechanically compliant, thermally conductive interface of claim 1, wherein the interface is selected from the group consisting of graphite, titanium boride, alumina trihydrate, alumina nitride, and mixtures thereof. 3. The thermally compliant thermally conductive interface of claim 2, wherein said particulate solid is alumina having a particle size range of about 1 to 50 microns. 4. The mechanically compliant thermally conductive interface of claim 1, wherein said compliant thermally conductive interface has a thickness between 0.010 inches and 1.00 inches. 5. The mechanically compliant thermally conductive interface of claim 4, wherein the thickness is between 20 and 1000 mils. 6. The mechanically compliant thermally conductive interface of claim 1, wherein said organosiloxane consists essentially of polydimethylsiloxane. 7. The mechanically compliant, thermally conductive interface of claim 6, wherein said chain extender comprises hydride terminated polydimethylsiloxane. 8. The mechanically compliant, thermally conductive interface of claim 7, wherein said chain extender comprises hydroxy-terminated polydimethylsiloxane. 9. A mixture consisting of 71% by weight alumina and the balance polydimethylsiloxane, and the range of forces required to achieve a compression of 10% of the original thickness is 1%.
The mechanically compliant, thermally conductive interface of claim 7, which is in the range of 0-200 psi. 10. A mixture comprising 71% by weight of alumina and the balance consisting of polydimethylsiloxane and the force required to achieve a compression of 50% of the original thickness is in the range of 40 to 1000 psi. A mechanically compliant, thermally conductive interface according to claim 7. 11. The mechanically compliant thermally conductive interface according to claim 6, wherein the thermal conductivity is in the range of 0.5 W / m · K (watt per meter per kelvin) to 4 W / m · K. 12. The mechanically compliant thermally conductive interface according to claim 6, wherein the filler is graphite. 13. The mechanically compliant, thermally conductive interface of claim 1, wherein the viscosity is in the range of 10 to 1000 centipoise.