Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-06-30
2002-12-24
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S313000, C430S316000, C430S318000, C430S322000, C438S637000, C438S638000, C438S672000
Reexamination Certificate
active
06497991
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to a method of producing a printed circuit board having through via conductors each having a through hole, and more specifically to a method of producing a printed circuit board wherein through holes of through via conductors are closed by resin fillings. The present invention further relates to a mask for carrying out the above described method.
Heretofore, for connection between wiring layers formed on the upper and lower surfaces of a printed circuit board, through via conductors have generally been used. In production of such a printed circuit board, the through holes of the through via conductors are closed by resin fillings so that an insulation resin layer formed over the through via holes can be flat or planar.
In this instance, the following method is known for closing the through holes of the through via conductors by resin fillings. In the first place, as shown in
FIG. 10
, a base
51
consisting of a substrate
50
and metal layers
52
covering the opposite upper and lower surfaces (though only the upper surface
51
A is shown) of the substrate
50
is prepared. The base
51
has a plurality of through via conductors
55
extending completely between the upper surface
51
A and lower surface of the base
51
. Each through via conductor
55
has a through hole
54
defined by the inner circumferential surface thereof. A mask
61
having filling holes
62
aligned with the respective through holes
54
is placed on the surface
51
A (printing surface). The through holes
54
are filled with resin paste by printing by the use of the mask
61
.
After the filling by printing, the base
51
is heated to cure the resin paste fi lings
57
and thereby form cured resin fillings
58
in the through holes
54
as shown in FIG.
11
.
Generally, the through holes
54
of the through via conductors
55
formed in the base
51
are not arranged at constant intervals but varying intervals. If the through holes
54
are filled with the same amount of resin paste
57
, a larger amount of resin paste
57
per unit area is applied to a surface
51
A region where the distance between adjacent two of the through holes
54
is smaller (the left-hand portion in
FIG. 10
) as compared with that applied to a surface
51
A region where the distance between adjacent two of the through holes
54
is larger (the right-hand portion in FIG.
11
).
In this instance, at the time of curing by heating, the resin paste
57
is once liquefied and spread over while wetting the surface
51
A of the base
51
, and thereafter cured. By observation of the surface
51
A of the base
51
after the curing by heating, it will be found, as shown in
FIG. 11
, that the cured resin
58
in the surface
51
A region where the distance between adjacent two of the through holes
54
is smaller protrudes from the surface
51
A of the base
51
more than that in the surface
51
A region where the distance between adjacent two of the through holes
54
is larger.
For this reason, when the unnecessary portion of the cured resin
58
is removed by grinding for thereby uncovering the surface of the metal layer
52
, much time is required for removing the largely protuberant portion of the cured resin
58
(the left-hand portion in
FIG. 11
) or it may possibly occur such a case wherein the largely protuberant portion cannot be ground sufficiently, thus allowing some portion of the cured resin
58
to remain unremoved. Further, in case the surface
58
A of the cured resin
58
has large undulations, a surface region (right-hand portion n
FIG. 11
) where only a small amount of resin
58
is present is ground excessively to cause even the metal layer
52
to be ground, thus causing the metal layer
52
to become thinner and, in the worst case, causing the substrate
50
to be exposed.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a method of producing a printed circuit board which enables, when through holes of through via conductors formed in a base is filled with resin paste and cured by heating, the surface of cured resin formed on the base to become nearly flat, thus making it possible to remove an unnecessary portion of the cured resin with ease and efficiency and therefore making it possible to obtain a high yield rate.
It is a further object of the present invention to provide a mask which is used in a method of producing a printed circuit board, of the foregoing character.
To accomplish the above objects, the present invention provides a method of producing a printed circuit board having a base provided with through via conductors having through holes closed by resin fillings. The method comprises preparing the base having the through via conductors having the through holes, filling the through holes of the through via conductors with resin paste in such a manner that, of the through holes, those which are arranged at smaller intervals are filled with a smaller amount of resin paste than those which are arranged at larger intervals, curing the resin paste, and removing an unnecessary portion of resin resulting from the curing of the resin paste and thereby forming the resin fillings.
The present invention further provides a mask for use in a method of producing a printed circuit board having a base provided with a plurality of through via conductors having through holes closed by resin fillings. The mask comprises a plurality of filling holes aligned with the through holes of the through via conductors, respectively, of the filling holes, those which are arranged at smaller intervals having a smaller cross sectional area than those which are arranged at larger intervals.
REFERENCES:
patent: 5660321 (1997-08-01), Ishida et al.
patent: 5888627 (1999-03-01), Nakatani
patent: 6010768 (2000-01-01), Yasue et al.
patent: 6181569 (2001-01-01), Chakravorty
patent: 6194024 (2001-02-01), Arldt et al.
patent: 6219253 (2001-04-01), Green
patent: 6251502 (2001-06-01), Yasue et al.
patent: 55-138296 (1980-10-01), None
patent: 10-75027 (1998-03-01), None
Baxter Janet
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
Walke Amanda C.
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