Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-16
2001-08-14
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S458000
Reexamination Certificate
active
06274650
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention is related to liquid encapsulants for electronics components, more specifically those based upon liquid epoxy resins.
2. Background Art
Polymer encapsulants, mostly epoxy encapsulants, are commonly used in IC packaging for thermal and moisture resistance. In recent years with higher integration of integrated circuits, IC chips have become smaller with larger chips. This produces problems such as packaging delamination and cracks caused by stress and moisture. For example, the solder joints in flip chip on board are easily broken caused by stress, causing the flip chip to fail, if underfill encapsulant materials are not used in the package. With underfilling by epoxy encapsulants, the reliability of flip chip on board devices will be significantly increased. Therefore, good performance of encapsulants in stress and moisture resistant is very important for the reliability of packages.
Liquid epoxy composite materials having inorganic fillers blended in liquid epoxy resins are often used as encapsulants for underfilling in flip chip and chip-size packages, and glob-top dispensing/stencil bringing in chip-on-board (COB) and ball grid aray (BGA) packages. Such epoxy encapsulants are commercially available in one-component or two-component products. The one-component products consist of a uniform premix of a base epoxy resin, a curing agent, and other additives which is a mainstay in the art because it is easier to use.
Currently some epoxy encapsulants incorporating acid anhydrides have several drawbacks. The encapsulant materials tend to absorb moisture which causes the materials to expand in volume and results in the degraded performance of the packages. Some epoxy resins, such as epichlorohydrin and bisphenols or other novolak resins, and cycloaliphatic epoxy resins, epoxy resins having incorporated therein hologen atoms like chlorine and brominc atoms, are commonly used for liquid encapsulants because they are liquid at room temperature. An imidazole curing agent was proposed to be used for the base epoxy resins.
U.S. Pat. No. 5,561,174 discloses liquid epoxy resin compositions comprising (A) a liquid epoxy resin, (B) a dimethylpolysiloxane having epoxy groups at both ends and (C) a dispersing agent comprising the reaction product of (C-1) a dimethylpolysiloxane having amino groups or carboxyl groups reactive with epoxy resins on its side chains or both ends and having phenyl groups or polyether groups for improving compatibility with epoxy resins on its side chains, and (C-2) an epoxy resin having the same structure as component (A).
U.S. Pat. No. 5,189,080 discloses an encapsulating resin for electronics components consisting of cycloaliphatic epoxy resin, a hardener, an accelerator, a filler, and optionally, a pigment. The hardener can be methylnadic anhydride and the filler can be amorphous silica.
U.S. Pat. No. 5,248,710 discloses flip chip encapsulating compositions comprising (A) an epoxy resin having at least two epoxy groups per molecule, (B) a silicone-modified epoxy resin, (C) an imidazole curing agent soluble in epoxy resin (A) and (D) fused silica filler.
U.S. Pat. No. 5,354,939 discloses stabilized epoxy resin compositions comprising (a) liquid epoxy resin, (b) filler comprising quartz flour, (c) a polyether polyol and (d) an organically modified sheet silicate.
U.S. Pat. No. 5,416,138 discloses epoxy resin compositions for sealing semiconductor devices, “comprising as essential components” (A) an epoxy resin containing 50-100 weight percent of a diglycidyl ether of a substituted bisphenol identified as formula (I), (B) a phenolic resin curing agent containing 30-100 weight percent of a specific phenolic resin curing agent identified by formula (II), (C) an inorganic filler and (D) a curing accelerator.
U.S. Pat. No. 5,439,977 discloses an acid anydride-containing one package epoxy resin composition “consisting indispensably of” (1) an epoxy resin having two or more epoxy groups per molecule, (2) an acid anhydride, (3) at least one of (a) a liquid latent curing accelerator, (b) a latent curing accelerator soluble in epoxy resins such as (1) and (c) a latent curing accelerator soluble in acid anhydride and (4) a dispersible latent curing accelerator.
U.S. Pat. No. 5,457,165 discloses an encapsulant of amine-cured epoxy resin blends comprising (a) a first liquid epoxy resin comprising either: (1) the diglycidyl ether of polyoxypropylene glycol; or (2) the diglycidyl ester of linoleic dimer acid; (b) a second liquid epoxy resin comprising the diglycidyl ether of 1,4-butanediol, present as 12-55 parts by weight; and (C) a stoichiometric amount of an epoxy resin curing agent selected from flexibilized polyamines or polyamides.
DISCLOSURE OF THE INVENTION
An objective of the present invention is to provide one-component liquid encapsulant materials for underfilling, stencil printing, and dispensing for package such as flip chip, CSP, and BGA, etc. The liquid encapsulant materials provided in this invention have a high glass-transition temperature (Tg), high adhesion, and good moisture and stress resistance. The preferred basic epoxy resin in the liquid encapsulants developed in this invention is poly(bisphenol A-co-epichlorohydrin) glycidyl end-capped with epoxy groups at its ends at an epoxy equivalent of 189.
In accordance with the present invention, a liquid encapsulating composition is provided which comprises a poly(bisphenol A-co-epichlorohydrin) glycidyl end-capped with epoxy groups at each end of the molecule. This family of epoxy resins is characterized by formula I below. Optionally, one or two aliphatic or cycloaliphatic diepoxy resins can be added to modify the properties of the liquid encapsulating composition. The compositions further comprise as a curing agent a diamine compound having amine groups at each end of the molecule. The diamine compound can be an aromatic, aliphatic or cycloaliphatic compound. The compositions also optionally comprise an inorganic oxide filler. The filler, when used, is soaked with a surfactant for surface treatment to enhance its adhesion to the epoxy resin. The surfactant is preferably a silane.
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Aylward D.
Dawson Robert
Institute of Microelectronics
Oppenheimer Wolff & Donnelly LLP
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