Compositions – Electrically conductive or emissive compositions – Free metal containing
Reexamination Certificate
2000-02-18
2001-05-29
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Free metal containing
C252S514000, C252S518100
Reexamination Certificate
active
06238597
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of preparing an anisotropic conductive adhesive (hereinafter referred to as “ACA”) for the interconnection of flip chips onto plastic substrates, which is superior in both electrical conductivity and mechanical reliability.
BACKGROUND OF THE INVENTION
Having been strikingly developed, recent semiconductor technology involves principally the integration of more than a million cells, the establishment of a great number of input/output (I/O) pins on non-memory devices, large die sizes, the radiation of extensive heat, high electrical performance, etc. In spite of its remarkable advance, the semiconductor technology is not completely practiced because electronic package technology has not yet developed to such a level as to back the semiconductor technology. In pursuit of high electric performance, microminiaturization/high density, low-power operation, multifunction, high-speed signal processing, permanent reliability, etc., the electronic package technology is one of the most important factors which have critical influence on the determination of a final product's values, including performance, size, price, reliability, etc. Indispensable applications of microminiaturized package assemblies exist in the recently rapidly growing electronic industries, for example, in the computer, information communication, mobile communication, and high-tech electronic appliance industries. In particular, flip chip technology finds numerous applications in the smart card, liquid crystal display (LCD), plasma display panel (PDP), computer, cellular phone, and communication system industries.
Such flip chip technology has been and is being developed from a connection process using solders to a connection process using conductive adhesives which have advantages of the ability to pitch microelectrodes at low costs, fluxless, environment-friendly processing, and low temperature processing.
Commercially available as an anisotropic conductive film/adhesive type and an isotropic conductive adhesive type, conductive adhesives are composed normally of conductive particles, such as Ni, Au/polymer, and Ag, and thermosetting or thermoplastic insulating resins. Undoubtably, a conductive adhesive which is of more reliability, lower resistance and higher adhesive strength guarantees a better flip interconnection on an organic substrate. For this, necessary is knowledge of the optimal values for the size, distribution, content, and strain modulus of the conductive particles. In addition, it is also required to develop an adhesive resin capable of being cured within a shorter time at a lower temperature, its preparation process, and an ACA which can afford a flip chip process of low cost.
Typically, ACAs are divided into a film type and a paste type. The invention is primarily to develop a paste type of ACAs, which are useful for the interconnection of flip chips on plastic substrates, with the aim of making simple the manufacture of them.
Because flip chip technology using conductive adhesives has not yet been standardized clearly, Hitachi and Sony, leading companies in the conductive adhesive field of the world, European universities which form a multinational research consortium in which conductive adhesives are under systematic study, and company research institutes of many countries keenly compete with each other to dominate the world market through the world standardization of their own products. In particular, electronic package technology, one of the most important fields in producing electronic products, attaches great importance to the materials to be used and their preparation processes. Under this condition, novel connection materials which can replace conventional solder material to meet the tendency toward environment-friendly products as well as guarantee electrical conductivity and reliability are needed and their development is being watched with keen interest.
Prior arts which are relevant to the invention include (1) no-flow underfill technology and (2) conventional ACA. Quite different from the invention, the former, in which an underfill is formed when a solder-formed substrate is connected onto a substrate, does not use conductive particles. The latter suffers from a problem in that it is not of high reliability owing to high thermal coefficient resulting from the existence of oily conductive particles in ACA.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the problems encountered in prior arts and to provide an ACA which is endowed with the electrical conductivity that conventional anisotropic conductive films have and the mechanical reliability that the underfill used in a solder flip chip shows, simultaneously.
In accordance with the present invention, there is provided a method of preparing anisotropic conductive adhesives for flip chip interconnection on organic substrates, in which an epoxy resin as a binder is mixed with a conductive material and a non-conductive material at room temperature for 3 hours and then, with a coupling agent and a curing agent at room temperature for 1 hour, whereby the anisotropic conductive adhesives can bond flip chips to the organic substrates with high mechanical reliability.
REFERENCES:
C.P. Wong et a.; High Performance No-Flow Underfills for Low-Cost Flip-Chip Applications: Material Characterization; IEEE Transactions on Components, Packaging, and Mfg. Technology; Part A, vol. 21, No. 3; Sep. 1998; pp. 1-9.
Gautam Sarkar et al.; Flip Chjip Interconnect Using Anisotropic Conductive Adhesive;Journal of Materials Processign Technologies;1999; pp. 1-7.
Paik Kyung Wook
Yim Myung Jin
Greer Burns & Crain Ltd.
Kopec Mark
Korea Advanced Institute of Science and Technology
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