Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-01-06
2001-01-23
Yoon, Tae (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S433000, C523S435000, C523S461000, C524S129000
Reexamination Certificate
active
06177489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a flame retardant epoxy resin composition which is suitable for semiconductor encapsulation and when cured, meets the flame retardance rating UL-94 V-0 without a need for flame retardants and remains stable at high temperature. It also relates to a semiconductor device encapsulated with the composition.
2. Prior Art
With the advance of semiconductor devices toward higher density, surface mount packages now become the mainstream in; the semiconductor technology. Surface mount packages are exposed to high temperatures of 215 to 260° C. during mounting. Packages encapsulated with conventional encapsulants have the problems that separation can occur at the chip-encapsulant interface and cracks generate in the encapsulant portion. Thus reliability after mounting is not insured.
Under the circumstances, encapsulants comprising biphenyl type epoxy resins featuring low moisture absorption and reflow crack resistance are widely employed in these years.
As compared with the conventional encapsulants, these encapsulants comprising biphenyl type epoxy resins are superior in reflow crack resistance owing to low moisture absorption and low modulus at high temperature, but inferior in reliability tests such as a high-temperature residence test because of their extremely low glass transition temperature.
Defects are induced by high-temperature residence because intermetallic compounds form at the joints between aluminum electrodes and gold wires of IC during high-temperature residence. This results in an increased resistance and eventually the breakage of wires. It is known that the formation of such intermetallic compounds is accelerated by the presence of Br
−
and Sb
3+
in the resin composition as a flame retardant. It is a common practice to use a combination of a brominated epoxy resin and antimony trioxide as the flame retardant.
This indicates that the high-temperature capabilities are improved if the flame retardant is omitted. Conventional formulations, however, cannot meet certain flame retardant standards, for example, the rating V-0 of Underwriter's Laboratories UL-94 unless the flame retardant is added.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a novel and improved flame retardant epoxy resin composition which is suitable for semiconductor encapsulation and when cured, meets the flame retardance rating UL-94 V-0 without a need for flame retardants and remains stable at high temperature. Another object of the invention is to provide a semiconductor device encapsulated with the cured composition.
We have found that an epoxy resin composition comprising (A) a crystalline epoxy resin whose solution in meta-cresol in a concentration of 30% by weight has a viscosity of lower than 80 centipoise at 25° C., (B) a curing agent having at least two phenolic hydroxyl groups in a molecule, and (C) silica can achieve the rating V-0 of the flame retardant standard UL-94 without a need for flame retardants including antimony trioxide and bromine compounds such as brominated epoxy resins. The composition remains stable when allowed to stand at high temperature. Then a semiconductor device encapsulated with a cured product of the composition is improved in high-temperature reliability. Advantageous results are obtained particularly when the epoxy resin does not contain a monovalent to tetravalent saturated aliphatic hydrocarbon structure having at least 3 carbon atoms in a molecule except for a closed or open ring glycidyl group, and the curing agent does not contain a monovalent to tetravalent saturated aliphatic hydrocarbon structure having at least 3 carbon atoms in a molecule.
Better results are obtained when the composition further contains at least one member of (D) an organopolysiloxane, (E) an organic phosphine oxide, (F) an amide group-containing release agent, and (G) an epoxy-free silane coupling agent.
In a first aspect, the present invention provides a semiconductor encapsulating epoxy resin composition comprising
(A) an epoxy resin which is crystalline and exhibits a viscosity of lower than 80 centipoise at 25° C. when measured as a solution thereof in meta-cresol in a concentration of 30% by weight,
(B) a curing agent having at least two phenolic hydroxyl groups in a molecule, the curing agent being present in such an amount that the molar ratio of the epoxy group in the epoxy resin to the phenolic hydroxyl group in the curing agent may range from 5/10 to 9/10, and
(C) 89 to 92% by weight of the entire composition of silica.
In a second aspect, the present invention provides a semiconductor encapsulating epoxy resin composition comprising
(A) an epoxy resin which is crystalline and exhibits a viscosity of lower than 80 centipoise at 25° C. when measured as a solution thereof in meta-cresol in a concentration of 30% by weight,
(B) a curing agent having at least two phenolic hydroxyl groups in a molecule, the curing agent being present in such an amount that the molar ratio of the epoxy group in the epoxy resin to the phenolic hydroxyl group in the curing agent may range from 5/10 to 9/10,
(C) 86 to 92% by weight of the entire composition of silica, and
(D) an organopolysiloxane in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the epoxy resin and the curing agent combined.
In a third aspect, the present invention provides a semiconductor encapsulating epoxy resin composition comprising
(A) an epoxy resin which is crystalline and exhibits a viscosity of lower than 80 centipoise at 25° C. when measured as a solution thereof in meta-cresol in a concentration of 30% by weight,
(B) a curing agent having at least two phenolic hydroxyl groups in a molecule, the curing agent being present in such an amount that the molar ratio of the epoxy group in the epoxy resin to the phenolic hydroxyl group in the curing agent may range from 5/10 to 9/10,
(C) 87 to 92% by weight of the entire composition of silica, and
(E) an organic phosphine oxide of the following general formula (2):
(O═PR
2
3
)
n
(2)
wherein R
2
is independently a substituted or unsubstituted monovalent hydrocarbon group or two R
2
groups, taken together, forms a cyclic structure and letter n is equal to 1, 2 or 3, in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the epoxy resin and the curing agent combined.
The composition may further contain (F) an amide group-containing release agent.
The composition may further contain (G) a silane coupling agent free of an epoxy group. Preferably, the epoxy resin does not contain a monovalent to tetravalent saturated aliphatic hydrocarbon structure having at least 3 carbon atoms in a molecule except for a closed or open ring glycidyl group, and the curing agent does not contain a monovalent to tetravalent saturated aliphatic hydrocarbon structure having at least 3 carbon atoms in a molecule.
Also contemplated herein is a semiconductor device encapsulated with a cured product of the epoxy resin composition defined above.
The epoxy resin composition of the invention exhibits high flame retardance although it does not contain conventional flame retardants such as antimony trioxide and bromine compounds, typically brominated epoxy resins. Even when left at high temperature for a certain period, a semiconductor device encapsulated with a cured product of the composition remains unaffected and reliable because the composition does not contain bromide and antimony ion sources which can promote the formation of intermetallic compounds. The epoxy resin composition of the invention is of great worth in the industry in that it does not contain antimony trioxide and bromine compounds which are detrimental to the human body and can pollute the environment.
DETAILED DESCRIPTION OF THE INVENTION
A first essential component, component (A), of the epoxy resin composition of the invention is an epoxy resin which is crystalline at room temperature (typically 25° C.). When the epoxy resin is dissolved in meta-cresol in a concent
Aoki Takayuki
Asano Eiichi
Ino Shigeki
Okuse Satoshi
Shiobara Toshio
Shin-Etsu Chemical Co. , Ltd.
Yoon Tae
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