A thermally conductive mechanically compliant pad including a quantity of gallium and/or indium alloy liquid at temperatures below about 120° C. and a boron nitride particulate solid blended into the liquid metal alloy to form a paste. The paste is then combined with a quantity of a matrix forming flowable plastic resin such as microwax, silicone wax, or other silicone polymer to form the thermally conductive mechanically compliant pad, the compliant pad comprising from between about 10% and 90% of metal alloy coated particulate, balance flowable plastic resin.
|
0. 9. A thermally conductive electrically-resistive mechanically compliant pad comprising:
(a) an indium containing alloy having a melt temperature of between about 40° C. and 120° C., and being in divided particulate form of between about 1 and 100 μm in diameter; and
(b) a polymeric resin material having a melt temperature of between about 40° C. and 120° C.
0. 8. A thermally conductive electrically-resistive mechanically compliant pad comprising a mixture of:
(a) between about 10% and 90% by volume of a paste, which paste includes a blend of:
(i) an indium containing alloy having a melt temperature of between about 40° C. and 120° C.;
(ii) thermally conductive particles, at least a portion thereof being dispersed within at least a portion of said indium containing alloy; and
(b) balance flowable plastic resin.
0. 7. A method of preparing thermally conductive mechanically compliant pads comprising the steps of:
(a) selecting a quantity of an indium containing alloy which has a melt temperature of between about 40° C. and 120° C.;
(b) treating said alloy to cause dispersal into divided form;
(c) combining said dispersed alloy with thermally conductive particles and blending the combination to form a paste; and
(d) combining said dispersed alloy containing paste with a quantity of a flowable plastic resin material to form a thermally conductive mechanically compliant pad with said thermally conductive mechanically compliant pad comprising between about 10% and 90% by volume of the combined dispersed metal alloy and thermally conductive particulate, balance flowable plastic resin.
1. A method of preparing thermally conductive mechanically compliant pads comprising the steps of:
(a) selecting a quantity of an indium containing alloy which has a melt temperature of between about 40° C. and 120° C.
(b) treating said alloy to cause dispersal into divided form;
(c) combining said dispersed alloy with a compatible surface active agent and thermally conductive particles and blended to form a paste; and
(d) combining said dispersed alloy containing paste with a quantity of a flowable plastic resin material to form a thermally conductive mechanically compliant pad with said thermally conductive mechanically compliant pad comprising from between about 10% and 90% by volume of the combined dispersed metal alloy and thermally conductive particulate, balance flowable plastic resin.
2. The method of
3. The method of
4. The method of
5. The method of
0. 10. A thermally conductive mechanically compliant pad as in
0. 11. A thermally conductive mechanically compliant pad as in
|
The present invention is a continuation-in-part of application Ser. No. 09/543,661, filed Apr. 5, 2000, now U.S. Pat. No. 6,339,120 entitled “METHOD OF PREPARING THERMALLY CONDUCTIVE COMPOUNDS BY LIQUID METAL BRIDGED PARTICLE CLUSTERS”, and continuation-in-part application Ser. No. 09/690,994, filed Oct. 17, 2000, now U.S. Pat. No. 6,624,224 entitled “METHOD OF PREPARING THERMALLY CONDUCTIVE COMPOUNDS BY LIQUID METAL BRIDGED PARTICLE CLUSTERS”, and application Ser. No. 09/865,778, filed May 25, 2001, now U.S. Pat. No. 6,649,325 entitled “THERMALLY CONDUCTIVE DIELECTRIC MOUNTS FOR PRINTED CIRCUITRY AND SEMICONDUCTOR DEVICES AND METHOD OF PREPARATION”, all of which are assigned to the same assignee as the present invention.
The present invention relates generally to a method of preparing thermally conductive interface materials and compounds for improving heat transfer from a heat generating semiconductor device to a heat dissipator device such as a heat sink or heat spreader. More specifically, the present invention relates to a method and/or technique for preparing a mixture of an indium alloy blended with a polymer matrix, the polymer being in the solid phase at room temperatures and with both the alloy and the polymer having a melting temperature of between about 40° C. and 120° C., preferably between about 40° C. and 100° C. These blends of metal alloy and polymer have been found to sharply reduce the thermal resistance or impedance which typically arises from a less-than-perfect contact between the boundaries or surfaces of a thermal interface positioned between the components of the assembly. More particularly, the present invention involves a process for blending a normally solid polymeric matrix with a low melting alloy of indium metal for forming an improved thermal management system for use in combination with high performance semiconductor devices.
The thermal impedance or resistance created between two components in a typical electronic thermal management assembly is increased when surface imperfections are present on the opposed surfaces of the two components. The causes of poor physical contact typically lie with macroscopic warpage of one or both surfaces, surface roughness, or other non-flat characteristics created on one or both of the opposed contact surfaces. Areas of non-intimate surface contact result in the creation of air-filled voids which are, of course, exceptionally poor conductors of heat. High thermal impedance resulting from poor thermal contact results in undesirable heating of electronic components which in turn accelerates the rate of failure of the components such as semiconductor components and comprising the assembly. Replacement of air gaps or voids with a thermally conducting medium comprising a good thermal management system has been found to sharply reduce the thermal impedance and/or resistance.
In the past, liquid metals have been proposed for incorporation in thermally conductive pastes for use with heat generating semiconductor devices. In some cases, liquid metals were not readily adapted for this purpose, primarily because of problems created with the tendency of the liquid metal to form alloys and/or amalgams, which altered or modified the thermal and other physical properties of the mounting systems. Other thermal interface materials are made by dispersing thermally conductive fillers in a polymer matrix. While most polymer matrices range in thermal conductivity from 0.1-0.2 W-m−1-K−, the properties of the fillers are quite varied. They include silica (2 W-m−1-K−), zinc oxide (10-20 W-m−1-K−), alumina (20-30 W-m−1-K−), aluminum nitride (100 W-m−1-K−), and boron nitride (200 W-m−1-K−). When placed in the thermal joint, these compounds are intended to displace air and reduce overall thermal impedance. Addition of thermally conductive fillers, generally consisting of fine particulates, improved the thermal conductivity of the compound filling the voids.
In our copending application Ser. No. 09/543,661, a number of low melting alloys are disclosed which are highly effective for use as thermal interfaces in thermal management systems for enhancement of percolation of thermal energy. The present invention provides additional advantages in thermal interfaces through the use of certain selected polymer matrices for retention of the low melting alloy, the matrices having melting points which are also low and, preferably, relatively close to the melting points of the retained alloys. These polymers as well as the alloys are in solid phase at room temperature, and this feature facilitates ease of handling of the thermal interface particularly during production and use.
In accordance with the present invention, improved interface materials have been developed based on incorporation of low melting alloys as fillers capable of altering their shape in response to heat and pressure. At room temperature, these fillers are in solid phase, as is the polymer matrix, with this combination of features facilitating ease of handling. In addition, these morphing fillers respond to heat and pressure by their ability to flow into and fill air gaps or voids that may be present in the matrix, thereby avoiding creation of standoff or poor particle-to-particle contact (see FIG. 2).
In those applications where the opposed surface areas are small, or alternatively are relatively flat, interfaces having thin cross-sections may be employed. Typically, in such applications, those dispersions utilizing only polymeric matrices having dispersed low melting alloys function well (see FIG. 3). For interfaces employing a laterally disposed mechanical standoff, or those subject to large warpage, it is normally desirable to utilize highly thermally conductive particulate fillers in combinations with the low melting alloys in order to create large heat percolating clusters (see for example FIG. 4).
In accordance with the present invention, an indium-containing alloy is selected which is in the solid phase at room temperature, while having a melt temperature of between about 40° C. and 120° C. The alloy is then subjected to a size reduction operation—typically by emulsifying, while in molten phase, in the polymer matrix of interest. A surface active agent may be added during the emulsification to enhance the rheological properties and dispersion stability. Alternatively, the size reduction of the metal alloy may be accomplished by blow or impact, or alternatively by grinding or abrasion, under cryogenic conditions. Depending upon the particular type of equipment and conditions under which the particulate is formed, it may be possible to add the surface active agent to the working material while undergoing size reduction process. The metallic powder can then be blended with a quantity of a matrix polymer which is likewise in the solid phase at room temperature, having a melt point of between about 40° and 100° C. to form a compliant pad. The polymer matrix is preferably selected from the group consisting of paraffin, microwax, and silicone waxes. The low melting alloy may also be blended with a particulate filler such as, for example, boron nitride or alumina with the resultant mixture being mechanically agitated in the presence of a compatible wetting agent to form a stable dispersion for ultimate blending with the polymer matrix.
It should be noted that while the melt temperatures for the polymer matrix and the metal alloy are both indicated as being between about 40° C. and 120° C., it is desirable that a differential be maintained between the actual melt temperatures. For example, it has been found desirable to select a polymer matrix having a melting temperature which is approximately 10° C. lower than that of the metal alloy. Other differential relationships may also be useful. While certain other metal alloys may be found useful, indium-based alloys are generally preferred for utilization in the present invention.
The physical properties of thermal interface compounds prepared in accordance with the present invention are such that conventional production handling techniques may be employed during assembly operations. In this connection, the compounds may be handled or formed into an interface device by stamping or they may be printed directly onto heat-transfer surfaces. Alternatively, they may be made into tapes that can be die-cut so as to be later applied directly onto the heat transfer surfaces.
Therefore, it is a primary object of the present invention to provide compositions of materials useful as thermal interface compounds, wherein a low melting metallic alloy is retained within a polymer matrix, and wherein each of these components is in the solid phase at room temperature, and has a melting temperature of between about 40° C. and 120° C. and preferably between about 40° C. and 100° C.
It is a further object of the present invention to provide an improved combination of components utilized to form a composition which is useful as thermal interface compounds, and wherein hard particulate fillers such as boron nitride and/or alumina may be employed in combination with an indium alloy, and thereafter blended into and retained within a polymeric matrix.
It is yet a further object of the present invention to provide an improved thermal interface compound which is dry and solid at room temperature, and which changes to liquid phase at moderately elevated temperatures, thereby permitting the compounds to be easily handled utilizing conventional handling techniques and yet respond effectively in a thermal management application.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawings.
In carrying out the steps of the present invention, an indium-containing alloy is initially selected with this alloy having a melt temperature of between about 40° C. and 100° C., it being understood that alloys having melt temperatures of up to about 120° C. may also find application. Preferably, the low melting indium alloy comprises indium alloys containing quantities of bismuth, tin, and/or zinc as set forth below.
The selected indium alloy is subjected to an emulsification step wherein the metal is reduced to a finely divided form. It is preferred that the metal alloy be reduced to particles which average about 1-100 μm in diameter. The size reduction or emulsification may be undertaken in a high shear mixer, with the addition of a compatible surface active agent at a point in this step.
Following size reduction, the metal particulate is blended with a polymer, with the blend being subsequently cured to form the polymeric matrix retainer. Alternatively, the materials may be compounded in liquid state creating an emulsion with metal droplets dispersed in the polymer.
In order to describe the preferred embodiments, the following examples are given:
TABLE I
Alloys which are prepared for use in the present
invention having the composition and melting points as
follows:
Melting
Indium
Bismuth
Sn
Zinc
Point
Alloy
(%)
(%)
(%)
(%)
(° C.
1
51
32.5
16.5
0
60
2
66.3
33.7
0
0
70
3
26
57
17
0
79
4
52.2
0
46
1.8
108
As surface active agents, silanes, titanates, zirconates and/or assorted surface active agents are preferred to improve rheology and stability of the dispersion, and particularly for creating a hydrophobic barrier. Surface treatments with surface active agents that work well for improving rheology as well as stability of the dispersion, especially against moisture, are alkyl functional silanes, such as for example octyl triethoxy silane (OTES). Another example is methyltrimethoxy (MTMS) silane. These silanes bind to the oxides on the surface of the metal particles, creating a durable hydrophobic barrier. Additionally, these silanes compatibilize the particles with the polymer matrix and reduce particle aggregation.
The following compositions have been prepared, with numbers being by weight:
TABLE II
40 μm
Boron
Matrix
Alloy 1
Nitride
OTES
Parts
Parts
Parts
Parts
by
by
by
by
Formula
weight
Vol %
weight
Vol %
weight
Vol %
weight
Vol %
1
1001
30
1200
52
100
15
12
3
2
1001
34
1000
48
83
14
10
4
3
1001
35
1200
61
0
0
12
4
4
1001
40
1000
56
0
0
10
4
5
1002
35
1200
61
0
0
12
4
6
1003
30
1200
52
100
15
12
3
1silicone wax consisting of siloxane backbones with pendant alkyl chains and having a melting point of 60° C.
2microwax, melting point 60° C.
3soft silicone polymer consisting of a reactive siloxane elastomer.
Typical properties of the formulations are set forth in Table III:
TABLE III
Thermal
Conductivity
Thermal Impedance4
Formula
(W/m-K)
(K-cm2/W
1
>7
0.25
2
5.0
0.20
3
1.8
0.20
6
>7
0.25
4ASTM D5470, flat surfaces, no mechanical standoff.
Compounds prepared pursuant to the formulations of Table III are varied. Formulations 3, 4 and 5, in particular, may be applied as coatings by typical coating techniques including hot stamp, screen printing, or applied to the heat transfer surface directly by other means. These coatings will typically have a cross-sectional thickness of less than about 10 mils.
For coatings of larger cross-section, those formulations containing a particulate filler, such as Formulations 1, 2 and 6 may find particular application. These coatings may be applied to carriers such as glass or polymer fabrics, plastic films or metal foils. When supported, the coatings may be handled with ease, thereby facilitating their use in production.
For those applications which require intimate contact, i.e., where the contact line is desired to be as thin as possible, Formula 3 is recommended, although those of Formula 4 and 5 are highly suited as well. In each event, the metal droplet will deform completely so as to reduce contact resistance without increasing standoff. See for example the demonstrative dispersions illustrated in FIG. 5.
For those applications requiring mechanical, standoff, formulations pursuant to Formula 1 are well suited, it being noted that this formulation has highly desirable thermal conductive properties. In addition, the metal droplets present in the formulation will continue to function for reduction of contact resistance, while portions of the metallic component will be present in larger percolating clusters for enhanced transfer of thermal energy. See, for example, the demonstrative percolating cluster dispersions of FIG. 6.
With attention now being directed to
As indicated above,
The preferred method is emulsification of the metal in molten form. This can either be done in-situ in the polymer matrix of interest or in another liquid medium, followed by separation and purification of the powder. Utilizing typical operating parameters, the powdered alloy is available in sizes ranging up to about 100 microns.
Surface treatment includes, preferably, the addition of a surface active agent such as, for example, octyl triethoxy silane (OTES) or methyl triethoxy silane (MTMS). These silanes bind to the oxides which readily form of the surface of the metallic particles to create a hydrophobic barrier. Additionally, they compatibilize the particles with the polymer matrix and reduce particle aggregation. Alternatively, or additionally, titanates or zirconates such as, for example, the barium or calcium salt forms, may be used.
As indicated hereinabove, particulate materials such as boron nitride and alumina may typically be employed to improve the thermal conductivity and stability of the blend. These particulate components may be present in a range up to about 15% by volume, although blends containing up to about 50% by volume may be employed successfully. When blended, the alloy coats the particulate, with the blending operation being undertaken with the alloy in the liquid phase.
As indicated, the polymer matrix is preferably selected from paraffin, microwax, and silicone waxes comprising alkyl silicones. For most purposes microwax having a melting point of about 50-60° C. has been found particularly suited for this application. As indicated above, it is generally desirable to utilize a polymer matrix which undergoes a phase change at a temperature of about 10° C. lower than the phase change temperature of the alloy.
It is generally preferred that this step by undertaken with both components in the liquid phase. As such, the materials are blended in a high shear mixer until the metal becomes thoroughly dispersed in the polymer, at which time it may be formed into the configuration desired for the thermal interface. Conventional techniques for preparing the coating may be utilized, with this operation being compatible with most liquid phase treatment operations.
As illustrated in
With reference to
With attention being directed to
With reference to
With attention now being directed to
Boron nitride or alumina particulate preferably ranges in size from about 1 micron and up to about 40 microns in diameter or cross-sectional thickness. It will be observed that the platelet-like configuration of boron nitride in particular provides a highly desirable configuration and combination when wetted with liquid metal. The effective boron nitride particle is illustrated in
One silicone wax utilized in the formulations of the examples is GP-533 (M.P. of 60° C.) (Genesee Polymer of Flint, Mich.), with these materials being, of course, commercially available. A microwax employed is M-7332 (M.P. of 55° C.) (Moore and Munger of Shelton, Conn.). Another polymer matrix used is a one-part soft reactive silicone elastomer (GE Toshiba Silicones of Tokyo, Japan).
One unusual and unexpected property or feature of formulations of the present invention is the electrical resistivity. When Formulation 1 is formed in a pad of thickness of 3-5 mils and interposed between opposed surfaces of a semiconductor device and a heat sink, the electrical resistivity of the pad has been found to be highly significant, having a value of up to about 1012 Ω·cm (Formulation 1, Table II).
It will be appreciated that the above examples are given for purposes of illustration only and are not to be otherwise construed as a limitation upon the scope of the following appended claims.
Misra, Sanjay, Elahee, GM Fazley
Patent | Priority | Assignee | Title |
10068830, | Feb 13 2014 | Honeywell International Inc | Compressible thermal interface materials |
10155894, | Jul 07 2014 | Honeywell International Inc | Thermal interface material with ion scavenger |
10174433, | Dec 05 2013 | Honeywell International Inc | Stannous methanesulfonate solution with adjusted pH |
10287471, | Dec 05 2014 | Honeywell International Inc | High performance thermal interface materials with low thermal impedance |
10312177, | Nov 17 2015 | Honeywell International Inc | Thermal interface materials including a coloring agent |
10428256, | Oct 23 2017 | Honeywell International Inc | Releasable thermal gel |
10428257, | Jul 07 2014 | Honeywell International Inc. | Thermal interface material with ion scavenger |
10501671, | Jul 26 2016 | Honeywell International Inc | Gel-type thermal interface material |
10781349, | Mar 08 2016 | Honeywell International Inc | Thermal interface material including crosslinker and multiple fillers |
11041103, | Sep 08 2017 | Honeywell International Inc. | Silicone-free thermal gel |
11072706, | Feb 15 2018 | Honeywell International Inc. | Gel-type thermal interface material |
11373921, | Apr 23 2019 | Honeywell International Inc. | Gel-type thermal interface material with low pre-curing viscosity and elastic properties post-curing |
Patent | Priority | Assignee | Title |
3226608, | |||
3248615, | |||
3793106, | |||
4129881, | Mar 18 1976 | CKD PRAHA, Oborovy podnik | Heat sink cooled, semiconductor device assembly having liquid metal interface |
4147669, | Mar 28 1977 | Rockwell International Corporation | Conductive adhesive for providing electrical and thermal conductivity |
4233103, | Dec 20 1978 | The United States of America as represented by the Secretary of the Air | High temperature-resistant conductive adhesive and method employing same |
4254431, | Jun 20 1979 | International Business Machines Corporation | Restorable backbond for LSI chips using liquid metal coated dendrites |
4323914, | Feb 01 1979 | International Business Machines Corporation | Heat transfer structure for integrated circuit package |
4398975, | Dec 25 1980 | Sony Corporation | Conductive paste |
4520067, | Jun 23 1982 | SOLVAY ADVANCED POLYMERS, L L C | Composition useful for making circuit board substrates and electrical connectors |
4550140, | Mar 20 1984 | SOLVAY ADVANCED POLYMERS, L L C | Circuit board substrates prepared from poly(aryl ethers)s |
4764327, | Jan 14 1986 | Mitsubishi Gas Chemical Company, Inc. | Process of producing plastic-molded printed circuit boards |
5012858, | Oct 20 1986 | Fujitsu Limited | Method of cooling a semiconductor device with a cooling unit, using metal sherbet between the device and the cooling unit |
5024264, | Oct 20 1986 | Fujitsu Limited, | Method of cooling a semiconductor device with a cooling unit, using metal sherbet between the device and the cooling unit |
5053195, | Jul 19 1989 | Microelectronics and Computer Technology Corp. | Bonding amalgam and method of making |
5056706, | Nov 20 1989 | Microelectronics and Computer Technology Corporation | Liquid metal paste for thermal and electrical connections |
5170930, | Nov 14 1991 | Stovokor Technology LLC | Liquid metal paste for thermal and electrical connections |
5173256, | Aug 03 1989 | International Business Machines Corporation | Liquid metal matrix thermal paste |
5198189, | Aug 03 1989 | International Business Machines Corporation | Liquid metal matrix thermal paste |
5225157, | Jul 19 1989 | Stovokor Technology LLC | Amalgam composition for room temperature bonding |
5328087, | Mar 29 1993 | Stovokor Technology LLC | Thermally and electrically conductive adhesive material and method of bonding with same |
5445308, | Mar 29 1993 | Microelectronics and Computer Technology Corporation | Thermally conductive connection with matrix material and randomly dispersed filler containing liquid metal |
5529836, | Jul 31 1992 | International Business Machines Corporation | Multilayer article comprising a toughened polycyanurate |
5538789, | Feb 09 1990 | ORMET CIRCUITS, INC | Composite substrates for preparation of printed circuits |
5565267, | Feb 09 1990 | ORMET CIRCUITS, INC | Composite substrates for preparation of printed circuits |
5827907, | Aug 30 1993 | IBM Corporation | Homo-, co- or multicomponent thermoplastic polymer dispersed in a thermoset resin |
5958590, | Mar 31 1995 | International Business Machines Corporation | Dendritic powder materials for high conductivity paste applications |
6339120, | Apr 05 2000 | Henkel IP & Holding GmbH | Method of preparing thermally conductive compounds by liquid metal bridged particle clusters |
6624224, | Apr 05 2000 | Henkel IP & Holding GmbH | Method of preparing thermally conductive compounds by liquid metal bridged particle clusters |
6649325, | May 25 2001 | The Bergquist Company | Thermally conductive dielectric mounts for printed circuitry and semi-conductor devices and method of preparation |
EP696630, | |||
EP708582, | |||
EP813244, |
Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
Sep 04 2001 | ELAHEE, GM FAZLEY | The Bergquist Company | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 034435 | /0829 | |
Sep 04 2001 | MISRA, SANJAY | The Bergquist Company | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 034435 | /0829 | |
May 04 2005 | The Bergquist Company | (assignment on the face of the patent) | / | |||
Mar 25 2015 | The Bergquist Company | Henkel IP & Holding GmbH | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 035779 | /0071 |
Date | Maintenance Fee Events |
Feb 20 2012 | M1552: Payment of Maintenance Fee, 8th Year, Large Entity. |
Mar 22 2016 | M1553: Payment of Maintenance Fee, 12th Year, Large Entity. |
Date | Maintenance Schedule |
Jan 01 2011 | 4 years fee payment window open |
Jul 01 2011 | 6 months grace period start (w surcharge) |
Jan 01 2012 | patent expiry (for year 4) |
Jan 01 2014 | 2 years to revive unintentionally abandoned end. (for year 4) |
Jan 01 2015 | 8 years fee payment window open |
Jul 01 2015 | 6 months grace period start (w surcharge) |
Jan 01 2016 | patent expiry (for year 8) |
Jan 01 2018 | 2 years to revive unintentionally abandoned end. (for year 8) |
Jan 01 2019 | 12 years fee payment window open |
Jul 01 2019 | 6 months grace period start (w surcharge) |
Jan 01 2020 | patent expiry (for year 12) |
Jan 01 2022 | 2 years to revive unintentionally abandoned end. (for year 12) |