Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-25
2002-10-22
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C257S789000, C257S793000, C428S413000, C523S427000, C523S457000, C523S459000, C525S488000, C525S524000, C525S533000
Reexamination Certificate
active
06469074
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a liquid epoxy resin composition used to seal a semiconductor device, etc., a semiconductor device sealed with the resin composition, and a process for producing the sealed semiconductor device.
BACKGROUND OF THE INVENTION
Epoxy resin compositions have excellent electrical characteristics and adhesive strength and are widely used in a variety of electric and electronic fields. In particular, they are used for sealing semiconductor devices to secure high sealing reliability. Methods of sealing semiconductor devices with an epoxy resin composition which are widely carried out include transfer molding using a powdered composition or potting using a liquid composition and a dispenser.
With the recent tendency of electronic equipment getting more and more mobile and functional, the demands for semiconductor packages of higher integrity, higher density, smaller thickness, and smaller weight have been increasing. To address these demands new types of semiconductor packages have emerged, such as exemplified by a ball grid array (BGA) (with which a high density is achieved by area array connections), chip scale packages (CSP), and multi-chip modules (MCM).
Where these new types of semiconductor packages are sealed by conventional sealing techniques using a molding die and a powdered sealing material, the achievable thickness reduction is limited, and wires tend to be deformed (wire sweep). Therefore, liquid sealing materials have now come to be used. Use of a liquid sealing compound is advantageous over the transfer molding method which includes two steps; the step of previously compacting a powdered sealing compound into a tablet and the step of plasticizing the tablet in a pot. However, the problem of the liquid sealing compound resides in that it is inferior to the powdered sealing compound in sealing workability and reliability. The superiority of the powdered sealing compound over the liquid one is attributed to invulnerability to hydrolysis in a moisture resistance reliability test because of a phenolic curing agent contained therein and its high adhesive strength to a chip. In addition, the sealing compound used in the transfer molding is solid (powder) in ambient temperature, allowing a filler to be incorporated in an increased amount and the resin to have an increased glass transition temperature (Tg), thereby to exhibit excellent solder resistance and heat shock resistance.
On the other hand, the choice of curing agents and cure accelerators that can be employed in liquid sealing compounds is limited because of restrictions that the resulting compound should be liquid at ambient temperature, be of one-pack type and of long pot life. Amine compounds and acid anhydrides are generally used as curing agents or cure accelerators but have the following disadvantages. Of the amine compounds, liquid aromatic ones are so reactive with an epoxy group only to give a short pot life. Although solid amines typically exemplified by dicyandiamide secure a long pot life, they require too high a reaction initiation temperature, and the resulting compound is hygroscopic and inferior in electrical characteristics. A cured epoxy resin, cured by the acid anhydride curing agent, tends to be inferior not only in moisture resistance reliability because the ester linkage in the crosslinked structure is susceptible to hydrolysis but also in heat resistance reliability due to insufficient chemical adhesion. The phenolic curing agents, which are used in powdered sealing compounds to be molded in a molding die, are solid at ambient temperature so that they are hardly applicable to liquid sealing compounds loaded with fillers. If used, they would greatly increase the viscosity of a liquid epoxy resin. Addition of a solvent could decrease the viscosity, but the solvent will cause voids in the cured product, which ruin the appearance and deteriorate reliability, hardly equaling to the powdered sealing compounds molded in a molding die in sealing performance. Moreover any of these known curing systems fails to satisfy both the requirements of a long pot life at room temperature and of quick curability at high temperature and therefore unsuited to such large-scale sealing as can be carried out by transfer molding.
Under these circumstances, it has been keenly demanded to develop a liquid sealing compound which has satisfactory workability and is not inferior in sealing reliability and curability to a powdered sealing compound to be molded in a molding die.
In carrying out sealing of semiconductor chips such as BGA or CSP, the chips are mounted on a printed wiring board and then sealed by overcoating. If the sealing resin has a high elastic modulus, the printed wiring board would be warped appreciably and becomes practically useless. Therefore, sealing compounds usually contain an agent for reducing the elastic modulus (hereinafter referred to as a low-elasticity component).
Low-elasticity components generally known in the art include polybutadiene rubber, silicone powder, and silicone oil. However, they have the following disadvantages. The polybutadiene rubber has low long-term heat resistance on account of the thermal deterioration (oxidation) of the double bonds. Although silicone resins are thermally stable, powder type ones tend to agglomerate and separate, migrating upward in liquid, and increase the viscosity of the liquid, failing to be dispersed uniformly, only to produce small effects in reducing elasticity. The silicone oil is liable to form an upper separate phase in a liquid epoxy resin sealing compound because of poor compatibility with the epoxy resin and its small specific gravity. Further, the silicone oil is apt to bleed out in the interface between the sealant and the package substrate and act like a parting agent to reduce the adhesion, which may lead to interfacial separation. Thus, an improvement on a low-elasticity component for a sealing compound is also demanded.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid epoxy resin composition for sealing a semiconductor device, which cures quickly to provide a cured resin securing moisture resistant and heat resistant reliability for semiconductor devices while retaining the merits of conventional liquid sealing compounds, i.e., being liquid at ambient temperature and having a low viscosity easy in handling and a long pot life.
It is another object of the invention to provide a liquid epoxy resin composition for sealing a semiconductor device, which possesses the above-described characteristics and, in addition, provides a cured product with low elasticity without involving such problems as agglomeration, upward migration or phase separation in liquid.
It is still another object of the invention to provide a semiconductor device which is sealed by using the liquid epoxy resin composition.
It is yet another object of invention to provide a process for producing the semiconductor device.
The present invention provides a liquid epoxy resin composition for sealing a semiconductor device which comprises (A) a cyanic acid ester, (B) an epoxy resin, (C) an inorganic filler, (D) a metal chelate and/or a metal salt, and (E1) an acid anhydride, wherein at least one of components (A) and (B) is liquid at room temperature, component E1 is liquid at room temperature, the weight ratio of component C to the total weight of the composition is 0.60:1 to 0.95:1, the weight ratio of component A to component B is 0.76:1 to 1.43:1, and the weight ratio of component E1 to the total weight of the composition except component C is 0.01:1 to 0.3:1.
The present invention also provides a liquid epoxy resin composition for sealing a semiconductor device which comprises (A) a cyanic acid ester, (B) an epoxy resin, (C) an inorganic filler, (D) a metal chelate and/or a metal salt, and (E2) a dihydrazide compound, wherein at least one of components A and B is liquid at room temperature, the weight ratio of component C to the total weight of the composition is 0.60:1 to 0.95:1, the weight r
Fukui Taro
Hashimoto Shinji
Hino Hirohisa
Kanagawa Naoki
Kitamura Kenji
Matsushita Electric & Works Ltd.
Sellers Robert E. L.
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