Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Die bond
Reexamination Certificate
1999-03-25
2001-10-02
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Die bond
C438S118000
Reexamination Certificate
active
06297564
ABSTRACT:
The present invention relates to electronic devices and, in particular, to electronic devices employing adhesive interconnections including plated particles.
Electrically conductive polymer adhesives have played a major role in electronic applications as conductive adhesives for forming electrical interconnections and as conductive inks for forming parts of electronic circuitry for more than 40 years. Most of the conductive adhesives used for such applications for microelectronics have been filled with silver particles or with silver-plated particles. While gold particles and silver-palladium-alloy particles have also been used, their use has been limited by their intrinsic high cost which is determined principally by the high cost of the precious metals employed therein, resulting in a cost differential of at least a factor of 20-50 times the cost of silver. Particles of other conductive materials, such as nickel, copper, and graphite, have been used in filled adhesives for certain specific applications, but are not suitable for electrically-conductive adhesives because of inherent conductivity limitations resulting from either the relatively higher electrical resistance of the nickel and graphite materials or the tendency of copper and nickel to form oxidation.
Silver and silver-plated particles are widely used because of their relative low cost and high electrical conductivity, for example, as shown in prior art U.S. Pat. Nos. 2,774,747, 2,849,631, 4,210,704, 4,410,457, and 4,695,404. One major drawback of silver-based conductors and particles arises from the fundamentally lower ionization energy of their outer-shell electrons which are easily ionized and thus migrate easily under the influence of an electrical field especially when facilitated by the presence of water and other sources of ions. Thus protection against this well-known silver-migration problem must be provided if interconnections or other electrical conductors are to be in close proximity to each other, as where interconnections are formed having a fine pitch (i.e. center-to-center spacing).
While gold and palladium particles overcome the silver migration problem, they have been much less used because of their high cost. Gold and palladium typically cost in the range of US$200-400 per troy ounce as compared to a cost of US$5-10 per troy ounce for silver. As the pitch of interconnections in both semiconductor-to-substrate level interconnections and the component-to-board level interconnections has become increasingly fine, avoidance of silver migration has increased the cost of the finished product. This is caused by the need for additional protective coatings or for protective dielectric underfill in the spaces between silver-based interconnections in order to achieve acceptable levels of resulting device reliability.
Although copper, nickel and aluminum are good electrical conductors in bulk form, they are poor conductors in the form of small particles because they oxidize relative easily. While plating with silver and other precious metals is a relatively well-established art, the adoption of such plating of precious metals other than silver onto particles of copper, nickel, aluminum and other metals for forming electrically-conductive adhesive interconnections has not been desirable or commercially practical because of the high intrinsic cost of the precious metals. The same is true for electroless plating of such precious metals other than silver over organic and inorganic particles, such as polymer spheres and powders, graphite, carbon particles and fibers, and glass powders or frits. Thus, silver and silver-plated particles were inexpensive and were commercially available, but precious-metal-plated particles were not.
Accordingly, there is a need for an electrically conductive adhesive that avoids the problem of silver migration at a cost that is substantially lower than that of the prior art gold, palladium and gold-palladium alloy particle systems.
To this end, an electronic device according to the present invention comprises a semiconductor chip having contact pads thereon, wherein the semiconductor chip is connected in a flip chip manner to a substrate having corresponding contact pads. Connections between corresponding contact pads on the semiconductor chip and on said substrate are made with a conductive adhesive including: an adhesive selected from the group consisting of thermosetting and thermoplastic polymer adhesives, and a multiplicity of core particles formed of a material other than a precious metal, wherein the core particles are plated with a precious metal selected from the group consisting of gold, platinum and palladium.
According to another aspect of the present invention, an electronic device comprises at least one electronic component having a plurality of contact pads on a first surface thereof and a substrate having a plurality of contact pads on a first surface thereof. The contact pads of the substrate are arranged in a pattern to correspond to the contact pads on the electronic component and the electronic component and the substrate are positioned with their respective first surfaces proximate each other. A plurality of conductive adhesive connections are between respective ones of the contact pads of the electronic component and of the corresponding contact pads of the substrate. The conductive adhesive includes an adhesive selected from the group consisting of thermosetting polymer adhesives, thermoplastic polymer adhesives, and combinations thereof. The conductive adhesive also includes a multiplicity of core particles formed of a material other than a precious metal that are plated with a precious metal selected from the group consisting of gold, platinum and palladium.
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Amerasia International Technology Inc.
Chaudhuri Olik
Dann Dorfman Herrell and Skillman, P.C.
Pizarro-Crespo Marcos D.
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