Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-10-05
2001-02-27
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...
C523S427000, C523S457000, C525S481000, C528S153000
Reexamination Certificate
active
06194491
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an encapsulant comprising an epoxy resin composition with good moldability and high reliability in use, and semiconductor devices in which such an encapsulant is applied.
While there is a steady trend toward reduction of size and thickness of semiconductor elements, we can also note a tendency for the number of pins to increase in the elements in line with the enhanced performance of these elements. This has mandatorily narrowed the interval of the outer leads connecting the semiconductor elements to the substrate, making substrate packaging harder to work. As a solution to this problem, it has been proposed to employ the outer shape designated “BGA” (ball grid array package) in place of conventional “SOP” (small outline package) or “QFP” (quad flat package), and certain elements of this outer shape are already in quantity production in some quarters.
BGA allows wide spacing of the soldering balls for joint as these soldering balls are formed at a part or over the whole surface of the backside of an element, so that this outer shape is suited for multi-pin packaging. However, since BGA is designed to apply an encapsulant on one side of a BT (bismaleimide triazine) substrate or a glass-reinforced epoxy substrate, the produced package necessarily has a bimetal structure and is therefore subject to warping due to the difference in coefficient of contraction between the substrate and the encapsulant.
In order to overcome this problem, various proposals have been made, such as combining a polyfunctional epoxy compound with a specific curing agent and/or a curing accelerator (JP-A-8-176277), or mixing the encapsulants differing by more than 20° C. in glass transition temperature (JP-A-8-213518), but none of these proposals have been found satisfactory.
SUMMARY OF THE INVENTION
The present invention is intended to provide an epoxy resin composition for semiconductor encapsulating, which composition has good moldability, high use reliability and also high warping resistance in use for BGA packaging, and semiconductor devices in which such a resin composition is applied as encapsulant.
The present invention provides an epoxy resin composition for semiconductor encapsulation, comprising:
(A) a biphenyl-type epoxy resin represented by the formula (1):
wherein n is an integer of 0 to 6; and R
1
to R
4
are the same or different and represent independently a hydrogen atom or an alkyl group having 10 or less carbon atoms;
(B) a curing agent represented by the formula (2):
wherein l and m are each an integer of 0 or greater; and n is an integer of 1 or greater; and preferably 0.03≦n/(l+m+n)≦0.05,
(C) a curing accelerator which is an addition product of a triphenylphosphine and p-benzoquinone,
(D) an inorganic filler contained in an amount of 85 to 95% by weight based on the total amount of the composition.
The present invention also provides a resin-encapsulated semiconductor device comprising a substrate, a semiconductor element mounted on the substrate, and a resin layer encapsulating the semiconductor element-mounted side alone of the substrate, said resin layer being formed with said epoxy resin composition.
DETAILED DESCRIPTION OF THE INVENTION
The epoxy resin composition for semiconductor encapsulation according to the present invention comprises:
(A) an epoxy resin of the formula (1):
wherein n is an integer of 0 to 6, and R
1
to R
4
are the same or different and represent independently a hydrogen atom or an alkyl group having 10 or less carbon atoms;
(B) a curing agent of the formula (2):
wherein l and m are each an integer of 0 or greater; and n is an integer of 1 or greater; and preferably 0.03≦n/(l+m+n)≦0.05,
(C) a curing accelerator which is an addition product of a triphenylphosphine and p-benzoquinone, and
(D) an inorganic filler which accounts for 85 to 95% by weight of the total amount of the composition, wherein preferably said curing agent (B) is contained in an amount of 1.0 to 1.4 equivalents to one equivalent of the epoxy resin (A).
It is said that, generally, the problems arise in substrate packaging when warpage of the package exceeds 150 microns, so that efforts are being made to suppress such warpage to, preferably, less than 100 microns. With the conventional technology, however, it has been difficult to hold the warpage below 100 microns in case the BGA outer shape was large.
Use of the epoxy resin composition of the present invention makes it possible to overcome the above problems.
In the present invention, an epoxy resin of the formula (1) and a curing agent of the formula (2) are used as essential components, but where necessary other epoxy resins and/or curing agents may be jointly used.
Other epoxy resins usable in the present invention are not subject to restrictions as far as they have 2 or more reactive groups in the molecule, but their ratio (equivalent percent) in the composition is preferably 10 to 40%. When their ratio is less than 10%, the effect of their use is not manifested, while when their ratio exceeds 50%, there can not be obtained satisfactory fluidity of the composition. More preferably, other epoxy resin is used in a ratio (equivalent percent) of 15 to 30%.
Other curing agents usable in this invention are also not subject to restrictions as far as they have 2 or more hydroxyl groups in the molecule, but their ratio (equivalent percent) in the composition is preferably 10 to 50%. When their ratio is less than 10%, their use effect is not recognized, while when their ratio exceeds 50%, the advantageous properties of the curing agents of the formula (2) are not manifested. More preferably, other curing agent is used in a ratio (equivalent percent) of 20 to 40%. For providing the best fluidity of the composition, the equivalent ratio of the curing agent to the epoxy resin is preferably 0.6:1~1.4:1, more preferably 0.95~1.30.
The curing agent used as component (B) is added in an amount of preferably 1 to 100 parts by weight, more preferably 5 to 95 parts by weight, per 100 parts by weight of the epoxy resin.
For the synthesis of the compounds of the formula (2), it is possible to employ, for example, the following intermolecular ring-closing reaction method comprising self oxidation of naphthol.
An incipient reaction of a phenol containing 20 to 90 mol % of a naphthol and an aldehyde is carried out with an acid catalyst in the same way as in the case of ordinary novolak resins. In case where formalin is used as the aldehyde, the reaction is conducted under reflux at a temperature of around 100° C. This reaction is continued for about one to 8 hours, and then the reaction system is heated to 120 to 180° C. while draining water from the system in the presence of a strong acid and/or a super-strong acid. This operation is carried out in an oxidizing atmosphere (e. g., in the air). 2- to 24-hour holding of this situation completes the synthesis of a compound of the formula (2). Thereafter, the unreacted monomers are removed to obtain a desired curing agent.
The naphthols usable for the synthesis include 1-naphthol, whose use is essential, 2-naphthol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, and the like. These naphthols may be used in combination.
The phenols other than naphthols usable for the above synthesis include phenol and the phenol compounds commonly used for the synthesis of the phenol resins, such as o-cresol, p-cresol, m-cresol, butylphenol, dimethylphenol, nonylphenol, allylphenol and the like. These phenols may be used either singly or as a mixture of two or more of them.
The aldehydes usable for the above synthesis include those commonly used for the synthesis of phenol resins, such as formaldehyde, acetaldehyde, benzaldehyde, salicylaldehyde and the like, which may be used either singly or as a mixture of two or more of them.
Such a phenol and an aldehyde are reacted in an aldehyde to phenol molar ratio of preferably 0.3-1.0 to 1 in the presence of an
Fujii Masanobu
Sue Haruaki
Yamada Shin-ya
Antonelli Terry Stout & Kraus LLP
Hitachi Chemical Company Ltd.
Sellers Robert E. L.
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