Compostion of epoxy resin, phenol-triazine-aldehyde condensate and rubber

The present invention provides an epoxy resin composition comprising: (a) an epoxy resin having two or more epoxy groups in each molecule; (b) a phenolic resin composition comprising a condensation product of: (i) a phenol; (ii) a compound having a triazine ring; and (iii) an aldehyde, the mixture or condensation product being substantially free from any unreacted aldehydes, or methylol groups; (c) a rubber component; and (d) a curing accelerator. The epoxy resin composition has minute protrusions having a maximum height (Ry) .ltoreq.1.0 .mu.m, formed on its surface by thermosetting at or above 80.degree. C. The invention also provides a process for manufacturing a multilayer printed-wiring board of the build-up type which has a formed copper plating layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an epoxy resin composition having a 
surface on which minute protrusions can be formed simply by thermosetting 
the resin composition. The composition is useful as an interlayer 
insulation material in a multilayer printed-wiring board of the build-up 
type consisting of alternate layers of conductor circuitry and insulating 
materials. The present invention also relates to a multilayer 
printed-wiring board containing the epoxy resin composition and to a 
process for manufacturing the same. 
2. Discussion of the Background 
One process which has been used for manufacturing multilayer printed-wiring 
boards comprises laminating copper foils onto an internal-layer circuit 
board having a circuit formed thereon, by using several prepreg sheets as 
insulating bonding layers. Each prepreg sheet is prepared by impregnating 
glass cloth with an epoxy resin and curing it to a B-stage. Interlayer 
continuity is achieved by through holes in an external layer. This process 
suffers from several disadvantages including high cost incurred by 
large-scale equipment and long production times required for molding the 
copper foils under heat and pressure using a laminating press. Also, the 
formation of a fine pattern is made difficult by an increased copper 
thickness due to the through-hole plating on the external layer. 
Attention has recently been drawn as a means for solving these problems, to 
a technique in which organic insulating layers are formed alternately on 
conductor layers of an internal-layer circuit board for use in a 
multilayer printed-wiring board of the build-up type. Japanese Patent 
Applications Laid-Open Nos. Hei 7-304931 and Hei 7-304933 disclose a 
process for manufacturing a multilayer printed-wiring board by coating an 
internal-layer circuit board having a circuit formed thereon with an epoxy 
resin composition, curing it under heat, forming an uneven roughened 
surface thereon with a roughening agent and forming conductor layers by 
plating. Japanese Patent Application Laid-Open No. Hei 8-64960 discloses a 
process for manufacturing a multilayer printed-wiring board by applying an 
undercoat adhesive, preliminarily drying it, bonding an additive adhesive 
in film form thereto, curing it under heat, roughening it with an alkaline 
oxidizing agent and forming conductor layers by plating. All of these 
processes have the drawback of being low in productivity, since they have 
many time consuming steps requiring strict processing controls, including 
not only the prolonged step of roughening with an oxidizing agent, but 
also preparatory steps such as mechanical polishing and chemical swelling. 
SUMMARY OF THE INVENTION 
In view of the problems associated with the production of multilayer 
printed-wiring boards of the build-up type, it is an object of this 
invention to develop an epoxy resin composition for use in a multilayer 
printed-wiring board, having a surface on which minute protrusions can be 
formed simply by thermosetting the resin composition. It is also an object 
of the invention to simplify the process for making a multilayer 
printed-wiring board. 
The above objects are achieved through the use of an epoxy resin 
composition comprising: (a) an epoxy resin having two or more epoxy groups 
in each molecule; (b) a phenolic resin composition comprising a mixture or 
condensation product of: (i) phenols, (ii) a compound having a triazine 
ring, and (iii) aldehydes, the mixture or condensation product being 
substantially free from any unreacted aldehydes, or methylol groups; (c) a 
rubber component; and (d) a curing accelerator. The epoxy resin 
composition has minute protrusions, which have a maximum height (Ry) 
.ltoreq.1.0 .mu.m, formed on its surface by thermosetting the composition 
at or above 80.degree. C. 
The process of this invention simplifies the manufacture of a multilayer 
printed-wiring board of the build-up type, having high heat resistance, 
since it is possible to form a copper plating layer of high adhesive 
strength without any mechanical grinding, or chemical swelling, by 
thermosetting the epoxy resin composition once it has been applied to the 
circuit board.

DETAILED DESCRIPTION OF THE INVENTION 
The epoxy resin having two or more epoxy groups in each molecule, which is 
used as component (a) according to this invention, is one which provides 
for an interlayer insulating material having sufficiently high heat and 
chemical resistance for long term board use, and good electrical 
properties. The epoxy resin may comprise, for example, one or more 
epoxides selected from bisphenol epoxy resins including: bisphenol A, 
bisphenol F, and bisphenol S epoxy resins; phenol novolak epoxy resins; 
alkylphenol novolak epoxy resins; naphthalene epoxy resins; 
dicyclopentadiene epoxy resins, an epoxidated product of a condensation 
product of phenols and aromatic aldehydes having phenolic hydroxyl groups; 
triglycidyl isocyanurate; alicyclic epoxy resins, and brominated products 
of any of the above epoxy resins. The composition may also contain a 
monofunctional epoxy resin as a reactive diluent. 
Examples of the phenolic resin composition used as component (b) according 
to this invention include those which are disclosed in Japanese Patent 
Applications Laid-Open Nos. Hei 8-253557 and Hei 8-311142, hereby 
incorporated in their entirety by reference. More specifically the 
phenolic resin comprises a mixture or condensation product of: (i) 
phenols, (ii) a compound having a triazine ring, and (iii) aldehydes, said 
mixture or condensation product being substantially free from any 
unreacted aldehydes, or methylol groups. Preferred resins are Phenolite 
7050 resins manufactured by Dainippon Ink & Chemical Industrial Co., Ltd. 
Phenolite resins are novolak resins containing a triazine structure as 
represented by structural formula (1) shown below. 
##STR1## 
The phenolic resin composition (b) is preferably present in an amount such 
that there are from 0.5 to 1.3 phenolic hydroxyl equivalents thereof 
relative to one epoxy equivalent of the epoxy resin (a). As proportions 
outside this range are used, the heat resistance of any final product 
decreases. 
Examples of the rubber component used as component (c) according to the 
present invention are polybutadiene rubbers, modified polybutadiene 
rubbers such as epoxy-, urethane- or (meth) acrylonitrile-modified 
polybutadiene rubbers, and (meth) acrylonitrile-butadiene rubbers 
containing carboxyl groups. The rubber component (c), is preferably 
present in an amount within the range of 5 to 50 parts by weight relative 
to a total of 100 parts by weight of the epoxy resin (a) and the phenolic 
resin composition (b). If the rubber component is present in amounts less 
than 5% by weight, it is not possible to obtain a satisfactorily uneven 
surface by thermosetting. Amounts exceeding 50% by weight result in an 
interlayer insulating material which is unacceptable for practical use 
because of its low heat resistance, electrical properties and chemical 
resistance. 
The curing accelerator used as component (d) according to the present 
invention can be one or more of those which are conventional in the art 
including imidazoles, tertiary amines, guanidines, or epoxy adducts or 
microcapsulated products thereof, and organic phosphine compounds, such as 
triphenylphosphine, tetraphenyl phosphonium and tetraphenyl borate. The 
curing accelerator is preferably present in an amount within the range of 
0.05 to 10 parts by weight relative to a total of 100 parts by weight of 
the epoxy resin (a) and the phenolic resin composition (b). Proportions of 
less than 0.05 part by weight result in insufficient curing. Proportions 
exceeding 10 parts by weight are not effective for any further 
acceleration of curing. In addition, as the proportion of curing 
accelerator increases above 10 parts by weight, heat resistance and 
mechanical strength decrease. 
It is also possible to include binder polymers, thermosetting resins and/or 
other conventional additives in the composition of the present invention. 
Examples of binder polymers which may be used are (brominated) phenoxy 
resins, polyacrylic resins, polyamide resins, polyamideimide resins, 
polycyanate resins, polyester resins and thermosetting polyphenylene ether 
resins. Examples of thermosetting resins which may be used are blocked 
isocyanate resins, xylene resins, radical forming agents and polymerizable 
resins. Examples of other additives which may be included in the 
composition of the invention include inorganic fillers such as barium 
sulfate, barium titanate, silicon oxide powder, amorphous silica, talc, 
clay or mica powder, organic fillers such as silicone powder, nylon powder 
or fluorine powder, a thickening agents such as asbestos, orben or 
bentone, silicones, fluorine or high molecular weight defoaming and/or 
leveling agents and adhesion promoters such as imidazoles, thiazoles, 
triazoles, or silane coupling agents. It is also possible to include 
conventional coloring agents, such as Phthalocyanine Blue, Phthalocyanine 
Green, Iodine Green, Disazo Yellow, titanic oxide or carbon black. 
The epoxy resin composition of the present invention may contain one or 
more organic solvents. Examples of organic solvents which may be used 
include ketones such as acetone, methyl ethyl ketone and cyclohexanone; 
acetic esters such as ethyl acetate, butyl acetate, cellosolve acetate, 
propylene glycol monomethyl ether acetate and carbitol acetate; 
cellosolves such as cellosolve and butyl cellosolve; carbitols such as 
carbitol and butyl carbitol; aromatic hydrocarbons such as toluene and 
zylene; dimethylformamide and dimethylacetamide. 
A multilayer printed-wiring board comprising the epoxy resin composition of 
the present invention can be prepared according to procedures known in the 
art. The epoxy resin composition may first be formed on a patterned 
internal-layer circuit board. The composition can be applied to the 
circuit board by any method known in the art including coating, screen 
printing and laminating. The composition is applied to the board, dried 
(if it contains an organic solvent) and thermoset. Compositions in the 
form of an adhesive film can be laminated on the board under heat, and 
thermoset. The internal-layer circuit board may, for example, be an 
epoxy/glass laminate, a metal board, a polyester board, a polyamide board, 
a BT resin board, or a thermosetting polyphenylene ether board, and may 
have a roughened surface. Thermosetting of the epoxy resin composition is 
carried out by heating it at or above 80.degree. C., preferably between 
100.degree. C. and 180.degree. C. for 15 to 90 minutes. The surface of the 
resin layer, as thermoset, has minute protrusions having a maximum 
roughness (Ry) .ltoreq.1.0 .mu.m (FIGS. 1 and 2). Although it is not clear 
why the protrusions are formed simply by thermosetting, it has been 
determined that no protrusions are formed on the surface of a resin layer 
which is comprised of a conventional phenolic curing agent, such as phenol 
or cresol novolak, a polyfunctional epoxy resin, and a rubber component 
(FIG. 3). It is assumed that the surface of a resin layer rises and forms 
minute protrusions when a rubber component, forming an island structure by 
phase separation during thermosetting, is added to a curing agent having a 
crosslinking group differing in reactivity from a phenolic hydroxyl group 
and active hydrogen in triazine. The formation of these protrusions makes 
it possible to eliminate any mechanical grinding or chemical swelling 
treatment for carrying out the subsequent roughening treatment 
efficiently. 
Then, the necessary through or via holes are made by a drill and/or a laser 
or plasma. Roughening treatment is performed by an oxidizing agent, such 
as permanganate, bichromate, ozone, hydrogen peroxide/sulfuric acid, or 
nitric acid. Since the surface of the resin layer already has minute 
protrusions, roughening is only necessary to remove any smear from the 
through holes. Roughening gives the protrusions an even better anchoring 
effect due to the fact that the rubber component is soluble in the 
oxidizing agent. Next, conductor layers are formed by electroless and/or 
electrolytic plating. If a plated resist having the reverse pattern from 
the conductor layers is formed, the conductor layers can be formed simply 
by electroless plating. After the conductor layers have been formed, 
annealing is done at 150.degree. C. to 180.degree. C. for 15 to 60 minutes 
to cure any residual unreacted epoxy resin and improve the heat resistance 
of the resin layer and the peel strength of the conductor layers to a 
further extent. 
Examples 
Having generally described this invention, a further understanding can be 
obtained by reference to certain specific examples which are provided 
herein for purposes of illustration only and are not intended to be 
limiting unless otherwise specified. 
Example 1 
An epoxy resin composition was prepared by dissolving 30 parts by weight 
(the proportions being all expressed in parts by weight throughout the 
following description) of a bisphenol A type epoxy resin (Epon 1001 of 
Yuka shell Epoxy Co., Ltd., having an epoxy equivalent of 469) and 40 
parts of a cresol novolak type epoxy resin (EPICLON N-673 of Dainippon Ink 
& Chemical Industrial Co., Ltd., having an epoxy equivalent of 215) as 
component (a) and 30 parts of a phenol novolak resin containing a triazine 
structure (Phenolite KA-7052 of Dainippon Ink & chemical Industrial Co., 
Ltd. having a phenolic hydroxyl equivalent of 120) as component (b) in 20 
parts of ethyl diglycol acetate and 20 parts of solvent naphtha under 
heating and stirring, and adding 15 parts of end-epoxidated polybutadiene 
rubber (Denarex R-45EPT of Nagase Chemical Industrial Co., Ltd.) as 
component (c), 1.5 parts of a crushed product of 2-phenyl-4,5-bis 
(hydroxymethyl) imidazole as component (d), 2 parts of finely divided 
silica and 0.5 parts of a silicone-based defoaming agent. 
Example 2 
An epoxy resin composition was prepared by dissolving 15 parts of a 
bisphenol A type epoxy resin (Epon 828EL of Yuka Shell Epoxy Co., Ltd., 
having an epoxy equivalent of 185), 15 parts of a bisphenol A type epoxy 
resin (Epon 1001 of Yuka Shell Epoxy Co., Ltd.) and 35 parts of a cresol 
novolak type epoxy resin (EPICLON N-673 of Dainippon Ink & Chemical 
Industrial Co., Ltd.) as component (a) in methyl ethyl ketone (hereinafter 
referred to as MEK) under heating and stirring, and adding 50 parts of a 
MEK varnish of a phenol novolak resin containing a triazine structure 
(Phenolite LA-7052 of Dainippon Ink & chemical Industrial Co., Ltd., 
containing 60% of nonvolatile matter having a phenolic hydroxyl equivalent 
of 120) as component (b), 10 parts of intramolecularly epoxidated 
polybutadiene rubber (Epolead PB-3600 of Daicel chemical Industrial Co., 
Ltd.) as component (c), one part of 
tetraphenylphosphonium-tetraphenylborate as component (d), 50 parts of a 
brominated phenoxy resin varnish (YPB-40-PXM40 of Tohto Chemical Co., Ltd, 
having a nonvolatile content of 40% by weight and a bromine content of 25% 
by weight and containing a solvent mixture of xylene, methoxypropanol and 
methyl ethyl ketone having a ratio of 5:2:8) and 2 parts of finely divided 
silica. The epoxy resin composition as prepared in varnish form was 
applied by a roller coater onto a PET film having a thickness of 38 .mu.m 
to form a layer having a dry thickness of 65 .mu.m, and was dried at 
80.degree. C. to 120.degree. C. for 10 minutes, whereby an adhesive film 
was obtained. 
Comparative Example 1 
An epoxy resin composition was prepared by using 26 parts of a phenol 
novolak resin (BRG-557 of Showa High Molecule Co., Ltd., having a phenolic 
hydroxyl equivalent of 104) instead of the 30 parts of a phenol novolak 
resin containing a triazine structure and otherwise repeating Example 1. 
Comparative Example 2 
An epoxy resin composition was prepared by repeating Example 1, but 
eliminating the 15 parts of an end-epoxidated polybutadiene rubber 
(Denarex R-45EPT of Nagase Chemical Industrial Co., Ltd.). 
Example 1 of Manufacture 
An internal-layer circuit board was formed from an epoxy-glass laminate 
clad on both sides with a copper foil having a thickness of 35 .mu.m, and 
the epoxy resin composition which had been prepared in Example 1 was 
applied thereon by screen printing, and dried at 120.degree. C. for 10 
minutes, and after its application and drying on the reverse side, too, it 
was thermoset at 150.degree. C. for 30 minutes. A photograph of the 
surface of the resulting resin layer as taken through a SEM is shown in 
FIG. 1. Its surface roughness as determined (by SURFCOM470A of Tokyo 
Precision Co., Ltd.) confirmed the formation of minute protrusions having 
a maximum height (Ry) of 2 .mu.m (JIS BO0601). Then, the necessary through 
or via holes were made by a drill and/or a laser, and after quick 
roughening with an alkaline oxidizing agent, such as permanganate, 
electroless and/or electrolytic plating was performed to make a four-layer 
printed-wiring board in accordance with a subtractive process. After 30 
minutes of annealing at 170.degree. C., the conductor was examined for its 
peel strength (JIS C6481) and showed an adhesive property as good as 1.0 
kg/cm. The four-layer printed-wiring board was also tested for its heat 
resistance by 60 seconds of dipping in a solder bath at 260.degree. C. and 
did not show any abnormal change in appearance. 
Example 2 of Manufacture 
An internal-layer circuit board was formed from an epoxy-glass laminate 
clad on both sides with a copper foil having a thickness of 35 .mu.m, and 
the adhesive film which had been prepared in Example 2 was laminated on 
both sides of the board by a vacuum laminator at a temperature of 
100.degree. C., a pressure of 1 kgf/cm.sup.2 and an atmospheric pressure 
of 5 mm Hg or below, whereafter the PET film was removed and the resin 
composition was thermoset at 150.degree. C. for 30 minutes. A photograph 
of the surface of the resulting resin layer as taken through a SEM is 
shown in FIG. 2. Its surface roughness as determined confirmed the 
formation of minute protrusions having a maximum height (Ry) of 4 .mu.m. 
Then, the necessary through or via holes were made by a drill and/or a 
laser, and after quick roughening with an alkaline oxidizing agent, such 
as permanganate, a plated resist having the reverse pattern from the 
conductor layers was formed to make a four-layer printed-wiring board in 
accordance with an additive process. After 60 minutes of annealing at 
150.degree. C., the conductor was examined for its peel strength and 
showed an adhesive property as good as 1.2 kg/cm. The four-layer 
printed-wiring board was also tested for its heat resistance by 60 seconds 
of dipping in a solder bath at 260.degree. C. and did not show any 
abnormal change in appearance. 
Comparative Example 1 of Manufacture 
An internal-layer circuit board was formed from an epoxy-glass laminate 
clad on both sides with a copper foil having a thickness of 35 .mu.m, and 
the epoxy resin composition which had been prepared in Comparative Example 
1 was applied thereon by screen printing, and dried at 120.degree. C. for 
10 minutes, and after its application and drying on the reverse side, too, 
it was thermoset at 150.degree. C. for 30 minutes. A photograph of the 
surface of the resulting resin layer as taken through a SEM is shown in 
FIG. 3. Nothing like minute protrusions was formed. An attempt was made to 
make a four-layer printed-wiring board by repeating Example 1 of 
Manufacture, but a blister was found in the conductor layers as plated. 
Comparative Example 1 of Manufacture 
An internal-layer circuit board was formed from an epoxy-glass laminate 
clad on both sides with a copper foil having a thickness of 35 .mu.m, and 
the epoxy resin composition which had been prepared in Comparative Example 
2 was applied thereon by screen printing, and dried at 120.degree. C. for 
10 minutes, and after its application and drying on the reverse side, too, 
it was thermoset at 150.degree. C. for 30 minutes. A photograph of the 
surface of the resulting resin layer as taken through a SEM is shown in 
FIG. 4. The measurement of its surface roughness gave an Ry value of 0.8 
.mu.m. Example 1 of Manufacture was repeated for making a four-layer 
printed-wiring board. A blister was, however, found in the conductor 
layers during 30 minutes of annealing at 170.degree. C. 
The results of Examples 1 and 2 and Example 1 and 2 of Manufacture confirm 
that the process of this invention enables the manufacture of a highly 
reliable multilayer printed-wiring board of the build-up type, having high 
heat resistance, since it is possible to form a copper plating layer of 
high adhesive strength without any mechanical grinding, or chemical 
swelling. According to Comparative Example 1 employing a conventional 
phenol novolak curing agent, and Comparative Example 2 not employing an 
rubber component, however, it was not possible to form an uneven surface 
having a satisfactory anchoring effect. The copper plating layer which was 
formed on the surface of the board in comparative Examples 1 and 2 had an 
adhesive strength which was too low to be practically acceptable. 
This application claims priority from Japanese Patent Application Nos. 
100057/1997 and 170052/1997, filed with the Japanese Patent Office on Apr. 
17, 1997 and on Jun. 26, 1997, respectively, the entire contents of which 
are herein incorporated by reference. 
Having now fully described the invention, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.