Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-07-05
2003-01-14
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S476000, C523S443000
Reexamination Certificate
active
06506822
ABSTRACT:
This invention relates to epoxy resin compositions having advantages including minimized formation of internal and surface voids, effective infiltration to semiconductor devices, and firm adhesion of cured compositions to substrates, and thus suitable for the encapsulation of semiconductor devices by potting, chip-on-bonding or screen printing.
BACKGROUND ART
Because of good cured physical properties, epoxy resin compositions are used in a wide variety of fields including electric and electronic fields. Upon application, they are given any suitable flow property, for example, an extremely low viscosity or a highly thixotropic state for ease of operation.
For the encapsulation of semiconductor devices, sealing methods including potting, chip-on-bonding (COB) and screen printing are now widely employed. The potting and COB methods require that the resin flow into very narrow gaps between gold wires extending from the semiconductor chip. The screen printing method requires that the resin maintain its shape after encapsulation. This means that a good compromise between thixotropy and flow must be found. Prior art liquid epoxy resin compositions suffer from the problem of short filling or infiltration.
Epoxy resin compositions also suffer from the problem of air bubbles resulting in defective parts. During potting or dripping, bubbles are often introduced, which cannot be removed during the curing step and are left as voids in the interior and on the surface. In the case of screen printing, bubbles are generated by a squeegee during printing and left as voids on the surface. In the case of transfer molding, air is carried in during flow from the gate to the cavity and left as internal voids.
It is well known to add surfactants to epoxy resin compositions in order to reduce voids. Known surfactants are fluorochemical surfactants such as Florade FC-170C, FC-430 and FC-431 from 3M-Sumitomo Co., Ltd. and silicone surfactants such as KF351, KF945 and KF618 from Shin-Etsu Chemical Co., Ltd. However, where silicone plasticizers are added to epoxy resin compositions, surfactants commonly used as anti-foaming agents are not effective for inhibiting the formation of bubbles. It is impossible to completely remove voids in such silicone component-containing compositions. A study has not been made on the anti-foaming problem associated with the sealing methods including potting, COB and screen printing. It is merely attempted to reduce the viscosity or thixotropy of the resin in order to improve infiltration.
SUMMARY OF THE INVENTION
An object of the invention is to provide epoxy resin compositions having advantages including minimized formation of internal and surface voids, effective infiltration to semiconductor devices, and firm adhesion of cured compositions to substrates.
We have found that in an epoxy resin composition comprising (A) an epoxy resin, (B) a curing agent and (C) a silicone stress-reducing agent, the addition of (D) a foam-suppressing composition comprising (D-i) an oil compound consisting of a hydrophobic organopolysiloxane of the general formula (1) shown below and finely divided silica, (D-ii) a hydrophilic polyoxyalkylene-modified silicone oil of the general formula (2) shown below, and optionally, (D-iii) a polyoxyalkylene polymer is effective for eliminating and breaking bubbles. As a consequence, the formation of voids within the interior or on the surface of a cured product is fully inhibited. The epoxy resin composition is given an ability to infiltrate into semiconductor devices. The composition is fully adherent to various substrates. The addition of foam-suppressing composition (D) does not affect the physical properties of the cured composition. Therefore, the resultant epoxy resin composition is advantageously employed in the encapsulation of semiconductor devices by such techniques as potting, COB and screen printing.
According to the invention, there is provided an epoxy resin composition comprising (A) an epoxy resin, (B) a curing agent, (C) a silicone stress-reducing agent, and (D) a foam-suppressing composition. The foam-suppressing composition (D) is comprised of:
(D-i) 5 to 60% by weight of an oil compound consisting of 100 parts by weight of a hydrophobic organopolysiloxane of the following general formula (1):
R
1
a
SiO
(4−a)/2
(1)
wherein R
1
is at least one group selected from hydroxyl groups and substituted or unsubstituted monovalent hydrocarbon groups of 1 to 18 carbon atoms, and “a” is a number of 1.9 to 2.2, having a viscosity of 10 to 500,000 centistokes at 25° C., and 0.1 to 20 parts by weight of finely divided silica having a BET specific surface area of at least 100 m
2
/g,
(D-ii) 5 to 95% by weight of a hydrophilic polyoxyalkylene-modified silicone oil of the following general formula (2):
R
4
R
2
2
SiO—(R
2
2
SiO)
x
(R
2
R
3
SiO)
y
—SiR
2
2
R
4
(2)
wherein R
2
which may be the same or different is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 18 carbon atoms, R
3
is a group of the formula: —R
5
O(R
6
O)
b
(R
7
O)
C
-R
8
wherein R
5
is a divalent C1-C4 hydrocarbon group, R
6
is ethylene, R
7
is propylene, R
8
is hydrogen or a monovalent organic group selected from the class consisting of C1-C6 alkyl, acetyl and isocyanate groups, b is an integer of 3 to 100, c is an integer of 0 to 100, R
4
is as defined for R
2
or R
3
, x is an integer of 5 to 100, and y is an integer of 1 to 10, having a cloud point in 1% aqueous solution of at least 40° C. and a viscosity of 10 to 100,000 centistokes at 25° C., and
(D-iii) 0 to 90% by weight of a polyoxyalkylene polymer having a molecular weight of 500 to 5,000. The foam-suppressing composition (D) is present in an amount of 1×10
−4
to 20 parts by weight per 100 parts by weight of components (A) and (B) combined.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Briefly stated, the epoxy resin composition of the invention is defined as comprising (A) an epoxy resin, (B) a curing agent, (C) a silicone stress-reducing agent, and (D) a foam-suppressing composition.
The epoxy resin (A) used herein is not particularly limited with respect to molecular structure, molecular weight and other factors as long as it has at least two epoxy groups per molecule. Examples of the epoxy resin which can be used herein include bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins; novolac type epoxy resins such as phenol novolac type epoxy resins and cresol novolac type epoxy resins; triphenolalkane type epoxy resins such as triphenolmethane type epoxy resins and triphenolpropane type epoxy resins; phenolaralkyl type epoxy resins, biphenylaralkyl type epoxy resins, stilbene type epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, and cyclopentadiene type epoxy resins. These epoxy resins may be used alone or in admixture of two or more.
Where liquid epoxy resin compositions are desirable, there may be used any epoxy resin which has at least two epoxy groups per molecule and is liquid at room temperature (typically 25° C.). Preferred are bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins, and naphthalene type epoxy resins.
The curing agent (B) used herein is not particularly limited with respect to molecular structure, molecular weight and other factors. Any compound known as the curing agent may be used as long as it has at least two functional groups capable of reacting with epoxy groups in the epoxy resin. Exemplary functional groups are phenolic hydroxyl groups, amino groups and acid anhydride groups (with the proviso that the compound may have at least one acid anhydride group). A variety of phenolic resins are useful, including phenolic resins having at least two phenolic hydroxyl groups per molecule, for example, novolac type phenolic resins such as phenol novolac resins and cresol novolac resins; xylylene-modified novolac resins such as p-xylylene-modified novolac resins, m-xylylene-modified novolac resins, and o-xylylene-modified novol
Ichiroku Nobuhiro
Shiobara Toshio
Wakao Miyuki
Birch Stewart Kolasch & Birch, LLP.
Moore Margaret G.
Shin-Etsu Chemical Co. , Ltd.
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