Heat-sealable connector sheet

Proposed is a novel heat-sealable connector sheet, by which very reliable electric connection can be obtained with electrode terminals on an electronic device or a circuit board, consisting of a flexible insulating plastic substrate sheet and a patterned electroconductive layer formed thereon from an electroconductive paste with an overcoating layer of an insulating melt-flowable adhesive. Different from the electroconductive pastes used in conventional connector sheets, the electroconductive paste used here is compounded with an appropriate amount of relatively coarse particles of an insulating material having elasticity, e.g., plastic resins. The patterned electroconductive layer is formed from such a composite conductive paste in such a fashion that the insulating particles are fully embedded in the conductive paste but forming protrusions on the surface of the patterned electroconductive layer which accordingly exhibits a rugged appearance.

BACKGROUND OF THE INVENTION 
The present invention relates to a heat-sealable connector sheet or, more 
particularly, to a connector sheet for making electrical connection 
between the electrode terminals on an electronic device, such as liquid 
crystal display units, electroluminescence display units, light-emitting 
diodes, electrochromic display units, plasma display units and the like, 
and the electrode terminals of the driving circuit therefor formed on a 
circuit board or between two sets of electrode terminals on different 
electric circuit boards. 
It is well established that electrical connection between two sets of 
electrode terminals as mentioned above can be achieved by using a 
heat-sealable connector sheet consisting of an electrically insulating 
substrate sheet having flexibility and a patterned layer formed by 
printing thereon with an electroconductive paste which is a composite of 
an insulating adhesive resin blended with fine particles having electric 
conductivity in such an amount that the electroconductive layer formed 
therefrom has anisotropic electroconductivity only in the direction 
perpendicular to the plane of the layer (see, for example, Japanese Patent 
Publications 55-38073 and 58-56996). 
The heat-sealable connector sheets of this type, however, cannot fully 
comply with the demand in the modern electronic technology which is 
constantly under a trend toward more and more compact design of the 
electronic instruments in which the pitch of the line-wise patterned 
electrode terminals in an array is decreasing to 0.3 mm, to 0.2 mm or even 
finer. When electrical connection is made between such finely patterned 
electrode terminals by using a heat-sealable connector sheet of the above 
described type, namely, short-circuiting is sometimes unavoidable between 
adjacent two terminals as a consequence of displacement of the 
electroconductive particles out of the proper position. This problem has 
been at least partly solved by the teaching in Japanese Patent Kohyo 
62-500828 and Japanese Patent Kokai 62-154746 according to which an 
overcoating layer is provided over the whole surface of the connector 
sheet with a melt-flowable insulating adhesive. When electrode terminals 
are connected by using such a connector sheet under heating and pressure, 
melt of the melt-flowable adhesive is driven off from the surface of the 
conductive line patterns to form a pool of the melt between the conductive 
lines to ensure good insulation between the conductive lines. 
The above proposed improvement in a conventional heat-sealable connector 
sheet, however, is far from a complete solution of the problems. To 
explain it, the electroconductive particles dispersed in the insulating 
adhesive matrix to form a conductive paste are usually formed from a metal 
or a carbonaceous material having high rigidity so that the particles 
cannot comply with the deformation or displacement of the insulating 
flexible substrate, electroconductive layer and the insulating overcoating 
adhesive layer in conducting heat-sealing with heating under pressure. The 
particles also may be subject to a microscopic displacement due to the 
residual stress in the layers after heat sealing. Therefore, troubles are 
sometimes caused in the assembly of electrode terminals constructed by 
using such a heat-sealable connector sheet such as failure of electrical 
connection, increase in the electric resistance between the thus connected 
terminals and the like during use resulting in a loss of reliability of 
the electric connection. 
The above described problem could of course be solved by replacing the 
electroconductive particles of high rigidity with particles of a polymeric 
material having flexibility. Indeed, a proposal is made for the use of 
particles of an elastic polymeric material having a plating layer of a 
noble metal on the surface thereof to impart electroconductivity. These 
noble metal-plated elastomer particles, however, have another problem that 
microscopic cracks are sometimes formed in the plating layer as a 
consequence of the difference in the hardness and other physical 
properties between the core particles and the surface-plating layer so 
that a trouble of electric corrosion may take place due to a trace amount 
of residual electrolyte on the thus exposed surface of the core particles 
remaining after the plating treatment of the particles with the noble 
metal. Needless to say, the expensiveness of such noble metal-plated 
particles is another disadvantage to prohibit industrialization of this 
technology. 
SUMMARY OF THE INVENTION 
The present invention accordingly has an object to provide a novel 
heat-sealable connector sheet which is free from the above described 
problems and disadvantages in the conventional heat-sealable connector 
sheets in which the electrically conducting patterned layer is formed from 
an electroconductive paste compounded with conductive fine particles and 
is capable of making electrical connection between electrode terminals 
with very high reliability even under adverse ambient conditions after 
heat-sealing. 
Thus, the heat-sealable connector sheet of the invention comprises: 
(a) a substrate sheet made from an electrically insulating material having 
flexibility; 
(b) a patterned electroconductive layer formed on one surface of the 
substrate sheet from an electroconductive paste compounded with 
electrically insulating particles, preferably, having elasticity in such a 
fashion that the electrically insulating particles are fully embedded in 
the electroconductive paste to form protrusions on the surface of the 
layer covered by the electroconductive paste; and 
(c) an overcoating layer of a melt-flowable adhesive on the surface of the 
patterned electroconductive layer, optionally, extending to the surface of 
the substrate sheet not covered by the patterned electroconductive layer. 
In a preferable embodiment of the above defined heat-sealable connector 
sheet, the electrically insulating particles dispersed and embedded in the 
electroconductive paste have a porous structure. In another preferable 
embodiment, an additional electroconductive layer of an electroconductive 
paste is interposed between the patterned electroconductive layer 
containing the electrically insulating particles and the substrate sheet 
so that the patterned electroconductive layer has a double-layered 
structure consisting of an underlying layer of an electroconductive paste 
containing no insulating particles and a surface layer of an 
electroconductive paste compounded with insulating particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As is described above, the most characteristic feature of the inventive 
heat-sealable connector sheet consists in the unique composite structure 
of the patterned electroconductive layer containing the insulating 
particles dispersed and embedded in the electroconductive paste to form 
the layer in a specified fashion. As a consequence of the unique structure 
of the electroconductive patterned layer, greatly improved reliability can 
be obtained by the use of the inventive connector sheet in the electrical 
connection between electrode terminals. 
The electrically insulating substrate, on which the patterned 
electroconductive layer is formed in such a pattern to match the 
arrangement of the electrode terminals to be connected therewith, 
preferably has flexibility so that the material thereof is selected 
usually from various kinds of polymeric materials in the form of a film or 
sheet having a thickness of 10 to 50 .mu.m though not particularly 
limitative depending on the intended application of the inventive 
connector sheet. Examples of the polymeric materials or plastic resins 
suitable for the substrate include polyimide resins, poly(ethylene 
terephthalate) resins, poly(ethylene naphthalate) resins, poly(butylene 
terephthalate) resins, polycarbonate resins, poly(phenylene sulfide) 
resins, poly(1,4-cyclohexane dimethylene terephthalate) resins, 
polyallylate resins, liquid-crystalline polymers and the like. 
The electroconductive paste, in which the insulating particles are 
dispersed, is in itself a composite material consisting of an organic 
insulating binder resin as the matrix and fine particles having electric 
conductivity by forming a dispersed phase in the matrix of the insulating 
binder. The type of the binder resin as the matrix phase of the 
electroconductive paste is not particularly limitative including 
thermoplastic and thermosetting resins, of which thermosetting ones are 
preferred in respect of the good heat resistance and mechanical stability 
after curing to withstand the compressive force encountered in the 
connecting work of electrode terminals by using the inventive connector 
sheet as compared with thermoplastic ones. It is optional according to 
need to admix the matrix resin with various kinds of known additives such 
as curing accelerators, levelling agents, dispersion stabilizers, antifoam 
agents, thixotropy-imparting agents and the like. 
The above described binder resin to form the matrix of the paste is 
compounded with electroconductive particles in order that the paste is 
imparted with electroconductivity. The material of the particles is 
usually selected from metals, e.g., silver, copper, gold, nickel, 
palladium and the like as well as alloys of these metals. Silver- or 
gold-plated particles of copper or other base metals as well as plastic 
resins are also suitable. The average particle diameter of the conductive 
particles should preferably be in the range from 0.1 to 10 .mu.m. The 
particle configuration of the conductive particles is not particularly 
limitative including irregularly granular, spherical, flaky, 
platelet-like, dendritic, cubic and the like. The amount of the conductive 
particles dispersed in the matrix of the binder resin is usually in the 
range from 10 to 950% by weight based on the binder resin in order to 
impart the paste with a sufficiently high electric conductivity. 
An electroconductive paste can be prepared by uniformly blending, in a 
specified proportion, the above described insulating binder resin and the 
electroconductive fine particles, if necessary, with dilution by the 
addition of an organic solvent. In the preparation of the inventive 
heat-sealable connector sheet, the electro-conductive paste must be 
further blended with electrically insulating particles of either an 
inorganic or organic material, of which polymeric materials more or less 
having elasticity are preferred such as poly(methyl methacrylate) resins, 
polyamide resins, polystyrenes, benzoguanamine resins, phenolic resins, 
epoxy resins, aramid resins, acrylonitrile-butadiene copolymeric rubbers, 
polychloroprene rubbers, silicone rubbers and the like. Polyamide and 
related resins such as nylons, aramid resins and polyimide resins are 
particularly preferable in respect of the good balance relative to the 
solvent resistance, elastic modulus, shapability into particles, 
oil-absorptivity, adhesion behavior and the like. It is also important 
that the polymeric material forming the insulating particles has a melting 
point of 80.degree. C. or higher or, preferably, 120.degree. C. or higher 
in order that the particles retain their particulate configuration even in 
the heat sealing works usually conducted under pressure at a temperature 
of 80.degree. C. or higher. When particles made from a rigid inorganic 
material are used as the insulating particles in the inventive connector 
sheet, troubles may be caused in the connecting work of electrode 
terminals with the connector sheet due to eventual fracture of the 
insulating particles by the compressive force applied to the connector 
sheet at an elevated temperature, especially, when the material of the 
particles is relatively brittle. Even if no fracture of the insulating 
particles take place, another possible problem is that the layer of the 
electroconductive paste covering the protruded point of the particle is 
eventually pierced through by the sharp point of the particles to expose 
the insulating particles as uncovered with the electroconductive paste 
greatly decreasing the reliability in the electric connection with the 
connector sheet. The particle configuration of the insulating particles is 
also not particularly limitative including irregularly granular, 
spherical, flaky, platelet-like, dendritic cubic ones. It is sometimes 
preferable that at least the surface layer of the insulating particle has 
a porous structure with a porosity in the range, for example, from 5 to 
80%. 
Further, it is preferable that the material, assuming that it is a 
polymeric material, forming the insulating particles or at least the 
surface layer thereof has a value of solubility parameter not greater or 
not smaller by 2 or more or, more preferably, by 1 or more than the value 
of the binder resin forming the matrix phase of the electroconductive 
paste in order to ensure good compatibility between the matrix phase and 
the insulating particles dispersed therein. This condition is also 
favorable to prevent piercing of the electroconductive patterned layer by 
the points of the insulating particles by virtue of the good adhesion 
between the phases. 
The particle diameter d which the insulating particles should have depends 
on the thickness t of the electroconductive patterned layer, which is 
usually in the range from 5 to 30 .mu.m, formed from the electroconductive 
paste. Preferably, the particle diameter d of the insulating particles 
should be at least one third or, more preferably, at least equal to t 
which is the thickness of the patterned layer formed from the 
electroconductive paste as measured at the point having no insulating 
particles therein. When the particle diameter d of the insulating 
particles is too small, protrusions can hardly be formed by the insulating 
particles with a covering layer of the electroconductive paste because the 
particles are fully embedded in the conductive layer forming a fiat and 
smooth surface without protrusions. The particle diameter d of the 
insulating particles should not exceed five times or, preferably, twice of 
the thickness of the layer t. In addition, the width w of the patterned 
line-wise electroconductive layer should also be taken into consideration 
in the selection of the particle diameter d when the value of w is small. 
For example, the particle diameter d should be smaller than the line width 
w or, preferably, a half of the line width w. When the particle diameter d 
is too large, difficulties are encountered in forming a finely patterned 
lines with such a conductive paste containing coarse insulating particles. 
Usually, for example, the insulating particles should have a particle 
diameter in the range from 1 to 100 .mu.m. 
The amount of the insulating particles to be blended with the 
electroconductive paste is also important. Namely, it is preferable that 
the insulating particles are distributed uniformly throughout the area of 
the electroconductive patterned layer in a density of at least 20 
particles or, more preferably, at least 50 particles per square millimeter 
on an assumption that no overlapping of particles is formed within the 
layer in the direction perpendicular to the plane of the layer. As a rough 
measure, the insulating particles are Compounded in an amount of 5 to 500 
parts by volume or, preferably, 5 to 100 parts by volume per 100 parts by 
volume of the electroconductive paste. 
The patterned electroconductive layer of the inventive heat-sealable 
connector sheet is formed from the above described composite conductive 
paste containing the insulating particles by a known method which is most 
conveniently a method of screen printing by using an appropriate screen 
having a mesh opening wide enough to pass the relatively coarse insulating 
particles. When the above described various parameters are adequately 
selected or controlled relative to the formulation of this composite 
conductive paste, protrusions are formed on the surface of the thus formed 
patterned layer by being raised by the underlying insulating particles 
thus to give a rugged surface of the patterned conductive layer which 
should preferably have a surface roughness of 2 to 80 .mu.m. For example, 
even when the patterned conductive layer as formed by screen printing has 
a smooth surface without protrusions, the portions of the layer not 
supported by the insulating particles therein come to have a decreased 
thickness or to shrink along with evaporation of the solvent contained in 
the paste because the portions raised by the insulating particles cannot 
shrink so much even by evaporation of the solvent resulting in formation 
of protrusions there. It is important in this case that none of the 
insulating particles are exposed bare without being covered by the layer 
of the electroconductive paste. In other words, the surface of the 
patterned conductive layer is formed from the conductive paste throughout 
with no insulating particles exposed bare. In this connection, the 
thickness of the covering layer of the electroconductive paste on the 
surface of the insulating particles in the protruded portions should be in 
the range from 0.1 to 50 .mu.m. 
Though not essential, it is preferable that the patterned electroconductive 
layer formed in the above described manner on one surface of the 
insulating substrate is overcoated with a layer of a melt-flowable 
insulating adhesive resin, which overcoating layer may optionally extend 
to the surface of the insulating substrate not bearing the patterned 
electroconductive layer. FIG. 1 of the accompanying drawing illustrates 
such a connector sheet by a cross sectional view as cut perpendicularly to 
the plane of the sheet. In this figure, the substrate 1 is provided on one 
surface with lines 2 as a patterned electroconductive layer which consists 
of an electroconductive paste 2a forming the matrix phase and insulating 
particles 2b embedded in the paste 2a but forming protrusions on the 
surface of the patterned electroconductive layer 2. The patterned lines 2 
of the electroconductive layer are overcoated with a layer 4 of a 
melt-flowable insulating adhesive, which, in this figure, is not limited 
to the surface of the patterned electroconductive layer 2 but extends to 
the surface of the substrate 1 not bearing the patterned electroconductive 
layer 2. 
Various kinds of melt-flowable insulating adhesive resins can be used for 
forming the overcoating layer 4 on the surface of the patterned 
electroconductive layer 2 having protrusions raised by the insulating 
particles 2b. Namely, the principal ingredient of such an adhesive can be 
selected from the group consisting of copolymers of ethylene and vinyl 
acetate unmodified or modified with carboxyl groups, copolymers of 
ethylene and an alkyl acrylate, e.g., ethyl acrylate and isobutyl 
acrylate, polyamide resins, polyester resins, poly(methyl methacrylate) 
resins, poly(vinyl ether) resins, poly(vinyl butyral) resins, 
polyurethanes, copolymeric SBS rubbers unmodified or modified with 
carboxyl groups, S-I-S type copolymers of styrene and isoprene, SEBS-type 
copolymeric resins of styrene, ethylene and butyrene modified or 
unmodified with maleic acid, polybutadiene rubbers, polychloroprene 
rubbers unmodified or modified with carboxyl groups, styrene-butadiene 
copolymeric rubbers, isobutylene-isoprene copolymers, 
acrylonitrile-butadiene copolymeric rubbers unmodified or modified with 
carboxyl groups, epoxy resins, silicone rubbers and the like. 
It is optional or rather preferable that the insulating adhesive for the 
overcoating layer 4 is admixed with a known tackifier according to need. 
Examples of suitable tackifiers include rosins, and derivatives thereof, 
terpene resins, copolymers of terpene and phenol, petroleum resins, 
coumarone-indene resins, styrene-based resins, isoprene-based resins, 
alkylphenol resins, phenolic resins and the like and they can be used 
either singly or as a combination of two kinds or more. Other optional 
additives in the insulating adhesive include reaction aids or crosslinking 
agents such as phenolic resins, polyols, isocyanates, melamine resins, 
urea resins, urotropine compounds, amines, acid anhydrides, organic 
peroxides, metal oxides, metal salts of an organic acid such as chromium 
trifluoroacetate, alkoxides of titanium, zirconium or aluminum, 
organometallic compounds such as dibutyltin oxide, photopolymerization 
initiators such as 2,2-diethoxy acetophenone and benzil, sensitizers such 
as amines, phosphorus compounds and chlorine compounds as well as curing 
agents, vulcanizing agents, modifiers, aging retarders, heat-resistance 
improvers, heat-conductivity improvers, softening agents, coloring agents, 
coupling agents, metal sequestering agents and so on. 
The overcoating layer 4 of the melt-flowable insulating adhesive can be 
formed on the surface of the patterned electroconductive layer 2 by any of 
known methods including screen printing, gravure printing, roller coating, 
bar coating, knife coating, spray coating, spin coating and the like 
because the overcoating layer 4 can extend over the surface areas of the 
insulating substrate sheet 1 not bearing the patterned electroconductive 
layer 2 although the method of screen printing is preferred. The 
overcoating layer 4 of the melt-flowable insulating adhesive should have a 
thickness in the range from 1 to 50 .mu.m. When the thickness thereof is 
too small, the desired effect which should be exhibited by the 
over-coating insulating adhesive layer cannot be obtained as a matter of 
course while, when the thickness is too large, failure in electric 
connection may be caused between the patterned electroconductive layer 2 
and the electrode terminal, for example, on a circuit board after 
heat-sealing. 
It is a convenient way that the thickness of the overcoating layer 4 of the 
insulating adhesive formed, for example, by screen printing is controlled 
by adjusting the viscosity or consistency by diluting the adhesive with an 
organic solvent. Suitable organic solvents naturally depend on the type of 
the adhesive resin but usually is selected from the group consisting of 
esters, ethers, ether esters, hydrocarbons, chlorinated hydrocarbons, 
alcohols and the like, of which esters, ketones and ether esters are 
preferred. Particular examples of the organic solvent include methyl 
acetate, ethyl acetate, isopropyl acetate, isobutyl acetate, n-butyl 
acetate, amyl acetate, methyl ethyl ketone, methyl isoamyl ketone, methyl 
n-amyl ketone, ethyl n-amyl ketone, di(isobutyl) ketone, methoxymethyl 
pentanone, cyclohexanone, diacetone alcohol, ethyleneglycol monomethyl 
ether acetate, ethyleneglycol monoethyl ether acetate, ethyleneglycol 
monobutyl ether acetate, methoxybutyl acetate, diethyleneglycol monomethyl 
ether acetate, diethyleneglycol monoethyl ether acetate, diethyleneglycol 
monoethyl ether acetate, diethyleneglycol monobutyl ether acetate, 
trichloroethane, trichloroethylene, di(n-butyl) ether, diisoamyl ether, 
n-butyl phenyl ether, propylene oxide, furfural, isopropyl alcohol, 
isobutyl alcohol, amyl alcohol, cyclohexanol, benzene, toluene, xylene, 
isopropyl benzene, petroleum spirit, petroleum naphtha and the like. 
FIG. 2 of the accompanying drawing illustrates a circuit board 3 bearing 
electrode terminals 5 after heat-sealing with the inventive heat-sealable 
connector sheet by a cross section. When the inventive heat-sealable 
connector sheet is pressed with heating against the circuit board 3 in 
such a disposition that each of the electrode terminals 5 on the circuit 
board 3 is in contact with one of the lines of the patterned 
electroconductive layer 2, the melt-flowable insulating resin 4 covering 
the surface of each of the conductive lines 2 is driven out from the space 
between the electrode terminal 5 and the conductive line 2 so as to 
establish electric connection therebetween provided that the thickness of 
the insulating adhesive overcoating layer 4 is not overly large while the 
insulating adhesive excluded from the space by melt-flowing is pooled 
between two conductive lines 2 to establish adhesive bonding of the 
circuit board 3 and the connector sheet and to ensure electric insulation 
between the two conductive lines 2 or hence between the two electrode 
terminals 5 even when flowing deformation of the conductive lines 2 takes 
place. 
The above described heat-sealable connector sheet of the invention is 
advantageous in respect of the high reliability of electric connection 
established therewith and the electric insulation between adjacent 
terminal electrodes 5. A problem in this connector sheet is that, when the 
width of each of the electrode terminals 5 and the arrangement pitch 
thereof are decreased finer and finer, formation of the patterned 
electroconductive layer 2 by screen printing is sometimes incomplete 
because the electroconductive paste 2a used for printing is compounded 
with relatively coarse insulating particles 2b. The inventors have arrived 
at a discovery that this problem can be solved when the patterned 
electroconductive layer 2 has a double-layered structure of which the 
underlying layer in contact with the substrate sheet 1 is formed from an 
electroconductive paste 2a containing no insulating particles and the 
surface layer, which comes into contact with the electrode terminals 5 on 
the circuit board 3 when the connector sheet is on use, is made from an 
electroconductive paste 2a compounded with electrically insulating 
relatively coarse particles 2b. A heat-sealable connector sheet of this 
type is illustrated in FIG. 3 by a cross section as cut perpendicularly to 
the plane of the sheet. 
As is understood from FIG. 3, the connector sheet of this type is prepared 
by forming a patterned electroconductive layer 2 on an electrically 
insulating substrate sheet 1 having flexibility and then providing an 
overcoating insulating melt-flowable adhesive layer 4 while the patterned 
electroconductive layer 2 has a double-layered structure consisting of an 
underlying layer 2A formed from an electroconductive paste and adhesively 
bonded to the substrate sheet 1 and a surface layer 2B which is formed 
from an electroconductive paste 2a compounded with insulating particles 
2b. The patterned electroconductive layer 2 consisting of two layers 2A 
and 2B can be formed by the method of screen printing in which the 
underlying patterned layer 2A is first formed by printing with a 
conventional electroconductive paste or ink and then the surface layer 2B 
is formed in the same pattern with an electroconductive paste 2a blended 
with insulating particles 2b. The thickness of the underlying conductive 
layer 2A is preferably in the range from 0.5 to 25 .mu.m and the thickness 
of the surface layer 2B is preferably in the range from 0.5 to 25 .mu.m 
while the protrusions on the surface of the patterned electroconductive 
layer should have a height of 2 to 80 .mu.m. The other requirements for 
the surface layer 2B are about the same as those for the single-layered 
patterned electroconductive layer 2 illustrated in FIG. 1. 
In the following, the heat-sealable connector sheet of the invention is 
illustrated in more detail by way of examples. 
Example 1 
An electroconductive paste for screen printing compounded with insulating 
particles was prepared in the following manner. Thus, an electroconductive 
paste was first prepared by uniformly blending 100 parts by of an epoxy 
resin of the bisphenol A type as an organic binder with 70 parts by weight 
of a silver powder consisting of flaky particles having a particle 
diameter of 1 to 3 .mu.m, 3 parts by weight of an amine-based curing 
accelerator for the epoxy resin and each 1 part by weight of a levelling 
agent, dispersion stabilizer, antifoam agent and thixotropy-imparting 
agent with dilution by adding a suitable volume of a 7:3 by volume mixture 
of toluene and methyl ethyl ketone. Thereafter, 30 parts by volume of a 
fine powder of a cured phenolic resin having an aver-age particle diameter 
of about 20 .mu.m and a compressive strength of 3.9 kgf/mm.sup.2 at 10% 
deformation were added to the above prepared electroconductive paste per 
100 parts by volume of the solid matter therein. The thus prepared 
composite electroconductive paste after drying and curing exhibited a 
compressive strength of 5.0 kgf/mm.sup.2 at 10% deformation. 
Screen printing was conducted with the above prepared composite 
electroconductive paste on a 25 .mu.m thick flexible substrate sheet of a 
poly(ethylene naphthalate) resin to form a patterned electroconductive 
layer having a thickness of 25 .mu.m after drying in a line-wise pattern 
with a pitch of 0.3 mm and width of each line of 0.15 mm. 
Separately, an insulating melt-flowable adhesive composition was prepared 
by uniformly blending 100 parts by weight of a carboxyl-modified NBR with 
40 parts by weight of an alkylphenol-based tackifier and each 1 part by 
weight of a phenolic resin as an aging retarder, titanium dioxide as a 
heat-resistance improver and aminosilane-based coupling agent followed by 
dilution with a 1:1 by volume mixture of petroleum naphtha and butyl 
Carbitol to give a solid content of 35% by weight. 
The substrate sheet provided with a patterned electroconductive layer 
thereon was overcoated with the above prepared insulating melt-flowable 
adhesive by using a bar coater in a thickness of 10 .mu.m after drying. 
Heat-sealable connector sheets of the invention were obtained by cutting 
the above obtained sheet in predetermined dimensions. 
The heat-sealable connector sheets prepared in the above described manner 
were each heat-sealed to a circuit board having electrode terminals of a 
transparent electroconductive ITO film, of which the surface resistivity 
was 30 ohm, by pressing at 140.degree. C. for 12 seconds under a pressure 
of 30 kgf/cm.sup.2. The thus prepared assembly of the circuit board and 
the connector sheet was subjected to the measurement of the electric 
resistance between an electrode terminal on the former and a line of the 
patterned electroconductive layer on the latter after an aging test 
carried out in two different ways. Thus, on one hand, the assembly was 
subjected to 1000 times repeated heating and cooling cycle each cycle 
consisting of a high-temperature stage at 85.degree. C. for 30 minutes and 
a low temperature stage at -30.degree. C. for 30 minutes. The measurement 
of the electric resistance was undertaken either immediately after the 
heating and cooling cycles for heat shock or after standing in an 
atmosphere of a relative humidity of 95% at 60.degree. C. for 240, 500 and 
1000 hours to give the values of the electric resistance in ohm shown in 
Table 1A below including the average value, maximum value and minimum 
value for each of the measuring conditions. On the other hand, the aging 
test was performed without the heat shock test by keeping the assembly in 
a high-temperature and high-humidity atmosphere of 95% relative humidity 
at 60.degree. C. and the measurement of the electric resistance was 
undertaken either as prepared or after standing for 240, 500 and 1000 
hours in the above mentioned atmosphere. The results are shown in Table 1B 
below. 
Comparative Example 1 
The same experimental procedure as in Example 1 was repeated excepting 
replacement of the particles of the cured phenolic resin compounded in the 
electroconductive paste with the same volume of silver-plated spherical 
particles of nickel having an average particle diameter of about 20 .mu.m 
with a coefficient of variation of the diameter of 8%, of which the 
compressive strength was 16.3 kgf/mm.sup.2 at 10% deformation. Tables 1A 
and 1B also show the results of the measurement of the electric resistance 
in ohm carried out in the same manner as in Example 1 after each of the 
aging tests carried out after the heating and cooling cycles and the 
high-temperature, high-humidity test, respectively. 
TABLE 1A 
______________________________________ 
Comparative 
Example 1 Example 1 
Av. Max. Min. Av. Max. Mn. 
______________________________________ 
Initial 242 265 221 315 484 285 
After 240 hours 
258 284 277 842 1256 517 
After 500 hours 
277 301 248 6.3k 18k 3.1k 
After 1000 hours 
289 325 255 -- .infin.* 
5.5k 
______________________________________ 
*line broken due to electric corrosion 
TABLE 1B 
______________________________________ 
Comparative 
Example 1 Example 1 
Av. Max. Min. Av. Max. Mn. 
______________________________________ 
Initial 249 272 224 385 427 346 
After 240 hours 
261 295 238 11k 36k 6.8k 
After 500 hours 
279 302 250 -- .infin.* 
45k 
After 1000 hours 
291 315 265 -- -- -- 
______________________________________ 
*line broken due to electric corrosion 
Example 2 
An electroconductive paste was prepared by uniformly blending 100 parts by 
weight of a curable resin mixture consisting of a saturated copolymeric 
polyester resin having an average molecular weight of 20,000 to 25,000, 
hydroxy value of 6.0 mg KOH/g, acid value of 1.0 mg KOH/g and solubility 
parameter of 9.2 and a blocked isocyanate which was a biuret trimer of 
hexamethylene diisocyanate blocked with methyl ethyl ketoxime with 870 
parts by weight of flaky silver particles having a particle diameter of 1 
to 3 .mu.m and each 5 parts by weight of a polymeric levelling agent and a 
finely divided silica powder as a thixotropy-imparting agent by dilution 
with 200 parts by weight of ethyl Carbitol to give an electroconductive 
paste. 
The above prepared electroconductive paste was admixed, per 100 parts by 
volume of the solid matter in the electroconductive paste, with 45 parts 
by volume of a nylon powder consisting of spongy porous particles of 30% 
porosity having a compressive strength of 3.0 kgf/mm.sup.2 at 10% 
deformation, of which the average particle diameter was about 30 .mu.m 
with a coefficient of variation of the particle diameter of 7%, as the 
insulating particles. 
Heat-sealable connector sheets were prepared in the same manner as in 
Example 1 by the method of screen printing with the above prepared 
electroconductive paste compounded with the porous nylon particles and 
subjected to the same evaluation tests as in Example 1 for the electric 
resistance between the electrode terminal of the circuit board and the 
patterned electroconductive layer of the connector sheet. Tables 2A and 2B 
below show the results obtained in these tests giving the values of the 
resistance in ohm obtained by the measurements after standing in a 
high-temperature, high-humidity atmosphere either following or before the 
heat-shock test, respectively. 
Examples 3 to 5. 
The experimental procedure in each of these Examples was just the same as 
in Example 2 described above excepting replacement of the porous nylon 
particles with the same volume of another porous nylon particles of one of 
other grades listed below. 
Example 3: average particle diameter about 15 .mu.m ; variation coefficient 
of particle diameter 4%; porosity 30% 
Example 4: average particle diameter about 80 .mu.m ; variation coefficient 
of particle diameter 8%; porosity 30% 
Example 5: average particle diameter about 30 .mu.m ; variation coefficient 
of particle diameter 120%; porosity 30% 
The results of the evaluation tests are also shown in Tables 2A and 2B. 
TABLE 2A 
______________________________________ 
Av. Max. Min. Av. Max. Min. 
______________________________________ 
Example 2 Example 3 
Initial 187 228 165 312 423 256 
After 240 hours 
199 239 168 366 506 299 
After 500 hours 
205 245 172 398 611 312 
After 1000 hours 
208 250 174 413 635 316 
Example 4 Example 5 
Initial 220 383 155 335 532 166 
After 240 hours 
249 419 168 402 712 215 
After 500 hours 
269 435 198 458 763 229 
After 1000 hours 
298 485 213 559 783 246 
______________________________________ 
TABLE 2B 
______________________________________ 
Av. Max. Min. Av. Max. Min. 
______________________________________ 
Example 2 Example 3 
Initial 194 235 173 293 398 232 
After 240 hours 
206 259 188 342 522 301 
After 500 hours 
212 268 201 426 729 326 
After 1000 hours 
222 284 213 455 755 339 
Example 4 Example 5 
Initial 235 371 153 355 592 141 
After 240 hours 
258 470 166 458 819 198 
After 500 hours 
271 489 196 649 993 247 
After 1000 hours 
358 689 229 764 1100 356 
______________________________________ 
Example 6 and Comparative Example 2 
A 25 .mu.m thick PET film as a substrate sheet was provided with a 
line-wise patterned electroconductive layer of a double-layered structure 
having a line width of 0.15 mm and a pitch of 0.3 mm by first printing 
with the electroconductive paste prepared in Example 1 before compounding 
with the insulating phenolic resin particles and then with the same 
electroconductive paste after compounding with the insulating phenolic 
resin particles followed by overcoating with the same insulating 
melt-flowable adhesive as in Example 1 to complete a heat-sealable 
connector sheet. The thickness of the layers formed by the first and 
second printings was 10 .mu.m and 20 .mu.m, respectively, each after 
drying and curing. 
For comparison, in Comparative Example 2, another heat-sealable connector 
sheet was prepared in just the same manner as above excepting replacement 
of the electroconductive paste for the surface layer compounded with the 
insulating phenolic resin particles with the same electroconductive paste 
as prepared in Comparative Example 1 by compounding with silver-plated 
nickel particles. 
These heat-sealable connector sheets were subjected to the evaluation tests 
in the same manner as in Example 1 to give the results shown in Tables 3A 
and 3B giving the values of the electric resistance in ohm obtained by the 
measurements after standing in the high-temperature, high-humidity 
atmosphere the either following or before the heat-shock test, 
respectively. 
TABLE 3A 
______________________________________ 
Comparative 
Example 6 Example 2 
Av. Max. Min. Av. Max. Mn. 
______________________________________ 
Initial 249 272 227 318 484 283 
After 240 hours 
252 287 239 532 840 251 
After 500 hours 
280 295 247 6.2k 17k 3.1k 
After 1000 hours 
295 322 262 -- .infin.* 
5.4k 
______________________________________ 
*line broken due to electric corrosion 
TABLE 3B 
______________________________________ 
Comparative 
Example 6 Example 2 
Av. Max. Min. Av. Max. Mn. 
______________________________________ 
Initial 248 272 223 386 429 345 
After 240 hours 
260 295 239 11k 36k 6.8k 
After 500 hours 
280 303 251 -- .infin.* 
46k 
After 1000 hours 
291 315 265 -- -- -- 
______________________________________ 
*line broken due to electric corrosion