Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2001-01-24
2003-10-21
Jenkins, Daniel J. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C419S038000, C419S037000
Reexamination Certificate
active
06635099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to the manufacture of heat sinks. More particularly, the invention relates to a process for forming molded, sintered heat sink articles from a composition comprising copper particles.
2. Description of the Related Art
Heat dissipation is essential in the field electronics and semiconductor components. These devices produce heat during operation and are typically housed within a substantially closed compartment. The high number of heat generating parts, coupled with their close proximity increases the need for proper cooling methods.
The ability to control and dissipate heat can be accomplished by the use of heat sinks. Heat sinks are generally known in the art. One known heat sink method includes a conductive metal structure having fins, which is thermally coupled to an electronic component to aid in reducing the temperature of the component. Another approach includes the use of a fan for blowing air over the electronic component. Another heat sink approach is described in U.S. Pat. No. 5,312,508 which discloses attaching a crimped wire mesh having a plurality of wire bends to an object requiring heat transfer.
Unfortunately, these known heat sinks and heat sink methods are expensive, unreliable, occupy too much space, and have limited effectiveness. It would therefore be desirable to formulate a heat sink which is efficient and inexpensive, while still being adaptable to a variety of heat dissipation requirements.
The present invention provides a solution to this problem. The invention provides a process for forming a heat sink which includes injection molding and sintering of a copper composition. Metal injection molding is a well known process for forming molded articles from metal particles. For example, see U.S. Pat. No. 5,746,957 which teaches a process for forming ceramic and/or metal articles from a composition comprising a ceramic and/or metal powder, a polysaccharide binder and a gel strength enhancing agent. The metal injection molding process generally involves injecting a moldable fluid composition into a mold of predetermined shape under conditions to form a shaped article, referred to as a “green body”. After forming a green body, an article may be densified by sintering, so that it may have useful strength and other physical and mechanical properties. According to the invention, a substantially uniform copper composition comprising at least one polysaccharide binder, water, and copper particles is formed, and is then molded under conditions sufficient to form a solid molded intermediate. The solid molded intermediate is then sintered at a sufficient temperature and for a sufficient time to form a heat sink. These heat sinks may be formed into a variety of shapes, and can be used in various electronic and thermo-mechanical applications.
SUMMARY OF THE INVENTION
The invention provides a process for forming a heat sink which comprises:
a) forming a substantially uniform copper composition comprising:
i) at least one gel forming polysaccharide binder;
ii) water; and
iii) copper particles having an average particle size in the range of from about 2 &mgr;m to about 40 &mgr;m;
b) molding the copper composition under conditions sufficient to form a solid molded intermediate; and
c) sintering the solid molded intermediate at a sufficient temperature and for a sufficient time to form a heat sink.
The invention also provides a process for forming a heat sink which comprises:
a) forming a fluid composition comprising:
i) at least one gel forming polysaccharide binder; and
ii) water;
b) heating the fluid composition to melt the binder;
c) blending copper particles into the fluid composition to thereby form a substantially uniform copper composition;
d) cooling the copper composition to thereby form a substantially solid copper composition;
e) shredding the substantially solid copper composition to form a feedstock;
f) optionally adjusting the moisture content in the feedstock to a level of from about 6% to about 8% moisture by weight of the feedstock;
g) molding the feedstock under conditions sufficient to form a solid molded intermediate; and
h) sintering the solid molded intermediate at a sufficient temperature and time to form a heat sink.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention provides a process for forming a heat sink. The first step in forming the heat sink of the invention is to form a substantially uniform copper composition comprising at least one gel forming polysaccharide binder; water; and copper particles, preferably having an average particle size in the range of from about 2 &mgr;m to about 40 &mgr;m.
The gel forming polysaccharide binder is first combined with the water to form a fluid composition. The gel forming binder is used primarily to achieve good flowability, good green strength of the molded component, and a high solids loading potential. The polysaccharide binder preferably comprises an agaroid. For the purposes of this invention, an agaroid refers to agar and any gums resembling agar, and derivatives thereof such as agarose. An agaroid is employed because it exhibits rapid gelation within a narrow temperature range, a factor which can increase the rate of production of articles. Additionally, the use of such gel-forming binders reduces the amount of binder needed to form a self-supporting heat sink article. Therefore, heat sinks produced using gel forming binders comprising agaroids can significantly enhance the quality of and stability of green bodies and sintered heat sink articles.
The preferred agaroids are those which are water soluble and comprise agar, agarose, carrageenan, and the like and combinations thereof, and most preferably comprise agar, agarose, and mixtures thereof. The gel forming binder preferably is present in an amount ranging from about 1.5% to about 10% by weight of the composition, more preferably from about 2% by weight to about 8% by weight of the copper composition, and most preferably from about 3% by weight to about 7% by weight of the copper composition.
The composition then contains water, preferably deionized water. The water is added in an amount sufficient to dissolve the gel forming binder and is preferably present in an amount sufficient to form a uniform mixture of the composition components. The composition may include an additional optional solvent such as an alcohol to aid blending of the composition components. The water is preferably present in an amount of from about 5% by weight to about 11% by weight of the copper composition, more preferably from about 7% by weight to about 11% by weight of the copper composition, and most preferably from about 8% by weight to about 10% by weight of the copper composition.
It is preferred that the fluid composition comprising the binder and the water is first heated to melt the binder. Copper particles are then blended into the fluid composition to thus form a substantially uniform copper composition. The characteristics of the copper powder chosen is important because the selection can influence and control the flowability, evaporation-condensation, lattice, grain boundary surface diffusion and sintering mechanisms of the moldable composition. The size distribution of the particles in the copper powder can also influence the solids loading and moldability of the composition. The shape of the particles is important for flow behavior and shape retention during thermal processing. Preferably the particles are substantially spherical. The powder preferably has an average particle size of from about 1 to about 200 &mgr;m and more preferably from about 1 to about 35 &mgr;m for powders. Should a combination of copper powders be used, then they are preferably blended to ensure that each powder is uniformly dispersed within the composition. This allows the additive and binder to perform their functions most effectively and ensures that maximum solids loading is obtained. The copper particles are preferably present in an amount of from about 50% by weight to about 97% by we
Behi Mohammad
Burlew Joan V.
Glandz George A.
LaSalle Jerry C.
Buff Ernest D.
Ernest D. Buff & Associates LLC
Fish Gordon E.
Jenkins Daniel J.
Rutgers The State University of New Jersey
LandOfFree
Aqueous nonferrous feedstock material for injection molding does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous nonferrous feedstock material for injection molding, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous nonferrous feedstock material for injection molding will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3112482