Printing – Stenciling – Stencils
Reexamination Certificate
2002-01-03
2004-08-17
Funk, Stephen R. (Department: 2854)
Printing
Stenciling
Stencils
C101S123000, C101S129000, C101S425000
Reexamination Certificate
active
06776090
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a plate for printing and a method of using it, which are employed in patterning of a paste, filling a paste in a through hole and the like to prepare two-sided or multilayered wiring boards for use in a variety of electronic equipment.
BACKGROUND ART
In recent years, as a reduction in size and an increase in assembly density are in progress in electronic equipment, an increasingly multilayered structure has been required of circuit boards not only in the industrial electronics area but also in the consumer electronics area. With such circuit boards, it has become absolutely necessary to develop a new inner via-hole joining method for connecting between the circuit patterns disposed on a plurality of layers and also a new and highly reliable structure. In this respect, a new technology is disclosed to realize a high density circuit board manufacturing method of new construction featuring an inner via-hole connection performed by the use of a conductive paste. (Refer to the Japanese Patent Application Unexamined Publication No. H6-268345.) A description is given to this circuit board manufacturing method in the following:
First, a conventional manufacturing method of two-sided circuit boards is described.
FIG.
8
(
a
) to FIG.
8
(
f
) show cross-sectional views of the steps constituting a conventional manufacturing method of two-sided circuit boards.
FIG. 9
is a perspective view of a conventional plate framework with an opening provided and a mask attached thereto.
FIG. 10
is a cross-sectional view of the foregoing conventional plate framework with an opening provided and a mask attached thereto. FIG.
11
(
a
) to FIG.
11
(
g
) show cross-sectional views of the paste filling steps performed according to a squeegeeing method.
In
FIG. 8
, the reference numeral
21
is a prereg sheet measuring 300 mm wide, 500 mm long and 150 &mgr;m thick and using a board material formed of a composite prepared by having a nonwoven fabric formed of all-aromatic polyamide fibers impregnated with a thermosetting epoxy resin. The reference alphanumeric characters
22
a
and
22
b
are mask films formed of a plastic film, respectively, measuring 300 mm wide and about 16 &mgr;m thick and having a Si-based mold release layer of less than 0.01 &mgr;m in thickness disposed on the surface thereof that is in contact with prereg sheet
21
. Polyethyleneterephthalate is used as such, for example.
As the method for putting together prereg
21
and mask films
22
a
and
22
b
, disclosure is made about a method for continuously attaching by adhesion mask films
22
a
and
22
b
on prereg sheet
21
with the resin content thereof melted by the use of a laminating machine. (See the Japanese Patent Application Unexamined Publication No. H7-106766.) The reference numeral
23
is a through hole, which is filled with conductive paste
24
to connect electrically to metal foils
25
a
and
25
b
, each measuring 35 &mgr;m in thickness, formed of copper and the like and stuck onto both surfaces of prereg sheet
21
, respectively.
The conventional manufacturing method of two-sided circuit boards comprises the steps of forming first through hole
23
on prereg sheet
21
, on both surfaces of which mask films
22
a
and
22
b
are attached by adhesion, respectively, [FIG.
8
(
a
)] at a predetermined position thereof by a laser beam machining method and the like as FIG.
8
(
b
) shows, and then filling conductive paste
24
in through hole
23
as FIG.
8
(
c
) shows. The method for filling conductive paste
24
comprises the steps of placing prereg sheet
21
having through hole
23
formed thereon on a stage of an ordinary printing machine (not shown in
FIG. 8
) and then filling conductive paste
24
in through hole
23
directly from the top of mask film
22
a
by shuttling two squeegees formed of urethane rubber and the like to and fro alternately. At this time, mask films
22
a
and
22
b
on prereg sheet
21
act as a print mask, respectively, and also serve as means for preventing the surface of prereg sheet
21
from getting contaminated.
A description is further given to the method for filling conductive paste
24
with reference to
FIG. 9
, FIG.
10
and FIG.
11
(
a
) to FIG.
11
(
g
). A squeegeeing method is used to fill conductive paste
24
. However, since mask films
22
a
and
22
b
designed specifically for use with prereg sheet
21
are put in place, mask
2
, which is formed of stainless steel, measuring about 3 mm in thickness and provided with an opening of an area of 250 mm by 450 mm larger than the effective paste filling area of prereg sheet
21
, is mounted on plate framework
1
of a plate for printing
10
for paste filling as FIG.
9
and
FIG. 10
show. A slanting area with a slanting angle about 15° provided in opening
4
of mask
2
in the squeegees forward moving direction (at the 450 mm side) for the whole purpose of facilitating the passage of the squeegee.
The process of filling conductive paste
24
comprises the steps of setting mask
2
on prereg sheet
21
, which is attached by adhesion with mask films
22
a
and
22
b
on both surfaces thereof, respectively, formed with through hole
23
thereon and disposed on stage
6
of a printing machine (not shown in
FIG. 11
) as FIG.
11
(
a
) shows, and lowering the position of only a moving forth squeegee
5
a
out of both moving forth squeegee
5
a
and moving back squeegee
5
b
, which are located above, made movable up and down and right and left, and can be applied with a pressing force, to a predetermined position on mask
2
and having moving forth squeegee
5
a
moved forward while keeping conductive paste
24
rolling with a pressing force applied thereto. Air is used as the source of a pressing force to be applied to squeegees.
As FIG.
11
(
b
) shows, moving forth squeegee
5
a
passes the slanting area of mask 2 and reaches the surface of prereg sheet
21
. Both moving forth squeegee
5
a
and moving back squeegee
5
b
are provided with the ability to move up and down freely according to the positions thereof while maintaining a pressing force to be applied thereto. Thereafter, as FIG.
11
(
c
) shows, moving forth squeegee
5
a
stops at a predetermined position on mask
2
after travelling on prereg sheet
21
and passing again another slanting area of mask
2
, moves upward and then let conductive paste
24
fall freely.
Next, as FIG.
11
(
d
) shows, only moving back squeegee
5
b
is made to move downward to a predetermined position on mask
2
. Then, as FIG.
11
(
e
) to FIG.
11
(
g
) show, by having moving back squeegee
5
b
moved over mask
2
and prereg sheet
21
in the same manner as moving forth squeegee
5
a
, the step of filling conductive paste
24
in through hole
23
is completed.
Then, as FIG.
8
(
d
) shows, mask films
22
a
and
22
b
are peeled off from both surfaces of prereg sheet
21
and metal foils
25
a
and
25
b
formed of copper and the like are superimposed on both surfaces of prereg sheet
21
, respectively, as FIG.
8
(
e
) shows. By having a pressing force applied to the foregoing laminate while heat being applied thereto by means of a heat press, not only prereg sheet
21
is compressed in the thickness direction thereof (t2=about 100 &mgr;m) but also prereg sheet 21 is joined by adhesion with metal foils
25
a
and
25
b
as FIG.
8
(
f
) shows. Meanwhile, metal foils
25
a
and
25
b
on the surfaces of prereg sheet
21
are connected electrically with each other via conductive paste
24
filled in through hole
23
formed in prereg sheet
21
at a predetermined position thereof. Then, circuit patterns (not shown in
FIG. 8
) are formed on metal foils
25
a
and
25
b
on the surfaces of prereg sheet
21
by selective etching, thus allowing a two-sided circuit board to be obtained.
However, according to the conventional method for filling a conductive paste as described in above, when the conductive paste is filled in by moving squeegees back and forth, the conductive paste is dropped freely by lifting a moving
Kondo Toshikazu
Maeda Mitsunori
Nakamura Shinji
Sugita Yuichiro
Tahara Hiroshi
Funk Stephen R.
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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