Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
2002-09-06
2004-01-20
Gupta, Yogendra N. (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
C252S500000, C252S511000, C428S620000, C523S400000, C523S205000, C523S466000, C528S033000, C257S778000
Reexamination Certificate
active
06680007
ABSTRACT:
This invention relates to conductive resin compositions having both the adherent, heat resistant and moisture resistant properties of epoxy and phenolic resins and the flexible and impact resistant properties of silicone resins and suitable for use in electrical and mechanical connection of electronic parts as a substitute for the existing solder and conductive resin compositions; and electronic parts using the same.
BACKGROUND OF THE INVENTION
For the electrical and mechanical connection of electronic parts, solders and low-melting alloys are now widely used as well as conductive resin compositions of a thermosetting resin loaded with a conductive filler such as silver powder.
In most solders, lead is added in order to lower the melting point, which is against the current prevailing climate aiming for environmental protection. The abolition of leaded solder is being proposed in many countries. In combination with solder, a flux based on higher fatty acid is often used to help the solder bond to substrates and chips, which complicates the assembly operation of electronic parts.
Known conductive resin compositions include amine cure type epoxy resins and addition cure type silicone resins. Of these, the amine cure type epoxy resins can cure at a low temperature within a short time into cured products which have a high glass transition temperature and heat resistance, but are undesirably rigid and brittle. Additionally, since the cured epoxy resins do not fully absorb stresses generated at the bond interface to electronic parts, there is a risk that in a thermal cycling test or thermal shock test, cracks and other defects may develop in the electronic parts or the cured resins. The amine curing agents are more hygroscopic than phenolic curing agents and have a risk that in a moisture resistant reliability test, they may cause corrosion to electrodes and conductors and other undesired problems.
On the other hand, the addition cure type silicone resins cure into flexible products which can absorb stresses, but are less adherent and less heat resistant than the epoxy resins. There is a risk of cured silicone resins arising undesired problems such as interfacial separation after they are allowed to stand at elevated temperatures. Curing accelerators commonly used in silicone resin compositions, typically platinum compounds have the drawback that curing reaction is substantially retarded by inhibitors having an unshared electron pair such as nitrogen, phosphorus and sulfur.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a conductive resin composition which has both the adherent, heat resistant and moisture resistant properties of epoxy and phenolic resins and the flexible and impact resistant properties of silicone resins, is capable of fully absorbing stresses generated at the bond interface, and is suitable for use in electrical and mechanical connection of electronic parts as a substitute for the existing solder and conductive resin compositions. Another object is to provide an electronic part using the same.
The present invention provides a conductive resin composition comprising (A) an epoxy resin, (B) a phenolic resin, (C) a curing accelerator, and (D) a conductive filler as essential components. Component (A) and/or (B) is a copolymer obtained by reacting an epoxy resin or phenolic resin having at least two structural units of formula (1) per molecule:
wherein R
3
is hydrogen or glycidyl, and R
4
is hydrogen or a monovalent hydrocarbon group of 1 to 6 carbon atoms, with an organopolysiloxane of average compositional formula (2):
(R
1
)
a
(R
2
)
b
SiO
(4−a−b)/2
(2)
wherein R
1
is a monovalent organic group containing an amino, epoxy, hydroxyl or carboxyl group, hydrogen, hydroxyl, alkoxy or alkenyloxy group, R
2
is a substituted or unsubstituted monovalent hydrocarbon group, letters a and b are positive numbers in the range: 0.001≦a≦1, 1≦b≦3, and 1≦a+b≦4, the number of silicon atoms per molecule is an integer of 1 to 1,000, the number of functional groups R
1
directly attached to silicon atoms per molecule is an integer of at least 1. The organopolysiloxane component in the cured composition does not form a phase separation structure. A weight ratio of component (D) to components (A) plus (B) is in the range: 300/100≦D/(A+B)≦1500/100.
The conductive resin composition of the invention possesses both the adherent, heat resistant and moisture resistant properties of epoxy and phenolic resins and the flexible and impact resistant properties of silicone resins, is capable of fully absorbing stresses generated at the bond interface, and is suitable for use in electrical and mechanical connection of electronic parts as a substitute for the existing solder and conductive resin compositions. The term “conductive” is electrically conductive throughout the specification.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The conductive resin composition of the invention uses (A) an epoxy resin as a base and (B) a phenolic resin as a curing agent. Either one or both of components (A) and (B) must be a silicone-modified resin, i.e., a resin modified with an organopolysiloxane.
Reference is first made to the silicone-modified resin.
The silicone-modified resin originates from an epoxy resin or phenolic resin which has at least two, preferably 2 to 10, and more preferably 2 to 5 structural units of formula (1) per molecule.
Herein R
3
is hydrogen or glycidyl:
and R
4
is hydrogen or a monovalent hydrocarbon group of 1 to 6 carbon atoms.
At least two structural units of formula (1) are included for the following reason. When the epoxy or phenolic resin is reacted with an organopolysiloxane, either one of R
3
and R
4
in formula (1) reacts with a functional group R
1
in formula (2). If only one structural unit of formula (1) is included and R
3
reacts with the functional group R
1
, then the epoxy or phenolic hydroxyl group is lost from the moiety of formula (1), which means that the function of epoxy or phenolic resin is lost. If only one structural unit of formula (1) is included and R
4
reacts with the functional group R
1
, then both the epoxy or phenolic hydroxyl group and the organopolysiloxane are attached to the same benzene ring, indicating that reactivity lowers due to a steric factor. If two or more structural units of formula (1) are included, a controlled blending ratio of the epoxy or phenolic resin and the organopolysiloxane makes it possible that only one of the epoxy or phenolic hydroxyl group and the organopolysiloxane be attached to some benzene rings, indicating possible maintenance of reactivity. Moreover, as compared with the inclusion of one structural unit of formula (1), the inclusion of two or more structural units of formula (1) increases the number of functional groups on the silicone-modified resin and hence, the crosslinking density of cured products, which leads to improved mechanical strength, heat resistance and moisture resistance.
Of the above-described epoxy and phenolic resins, those of the following general formula (3), (4) or (5) are desirable.
Herein R
3
is hydrogen or glycidyl,
R
4
is hydrogen or a monovalent hydrocarbon group of 1 to 6 carbon atoms,
n and m each are an integer of at least 0.
Illustrative examples of the epoxy and phenolic resins of formula (3), (4) or (5) are compounds of the structure shown below.
Herein R
3
is hydrogen or glycidyl,
R
7
is each independently hydrogen or an alkenyl group such as vinyl, allyl or propenyl,
R
8
is each independently
or
n and m each are an integer inclusive of 0.
The molecular weight of these epoxy and phenolic resins is not critical. They preferably have a lower molecular weight in order that the silicone-modified resin have a low viscosity and the resin composition be easy to work. Illustratively, n is 0 to 10, and m is 0 to 5. More preferably, n is 0 to 5 when R
5
is —CH
2
—, or 0 to 3 when R
5
is
and m is 0 to 3.
The other reactant from which the silicone-modified resin is derived is an organopoly
Honda Tsuyoshi
Shiobara Toshio
Birch Stewart Kolasch & Birch, LLP.
Gupta Yogendra N.
Shin-Etsu Chemical Co. , Ltd.
Vijayakumar Kallambella
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