Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-10-05
2002-05-07
Gaffin, Jeffrey (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S260000
Reexamination Certificate
active
06384344
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a board that has connection terminals formed on both the top and back surfaces thereof and on which electronic circuit parts are to be mounted.
BACKGROUND ART
A wiring board
21
for mounting electronic circuit parts, as shown in
FIG. 8
, for example, is known as one conventional printed circuit board for mounting a bare chip like a flip chip or a package like a BGA (Bump Grid Array).
This type of wiring board
21
has a substrate
22
that has conductor layers formed on both the top and back surfaces by mainly a subtractive method. A parts mounting area is provided in the center of the top surface of the substrate
22
. Formed densely in this area are multiple pads
23
which constitute a first pad group. The individual pads
23
correspond to bumps BP positioned on the bottom of a bare chip C
1
.
Multiple pads
24
which constitute a second pad group are formed on the peripheral portion of the back of the substrate
22
. Formed on those pads
24
are bumps
25
as projecting electrodes for connection to a mother board. Multiple through holes
26
are formed through the substrate
22
at the peripheral portion of the substrate
22
. Those through holes
26
are connected to the pads
23
on the top surface via a conductor pattern
27
, which is formed on the top surface of the substrate
22
. The through holes
26
are also connected to the pads
24
on the back surface via a conductor pattern
28
, which is formed on the back surface of the substrate
22
. Accordingly, the first group of pads
23
are electrically connected to the second group of pads
24
respectively on this wiring board
21
.
According to the conventional wiring board
21
, as shown in
FIG. 8
, wires temporarily led out to the peripheral portion on the top surface are led back toward the center on the back surface. The wires for connecting the pads
23
to the pads
24
therefore are longer than necessary, resulting in a poor wiring efficiency. The use of this wiring board
21
makes it difficult to increase the speed of signal transmission between electronic circuit parts to be mounted and the mother board.
To connect the pads
23
and
24
together by the shortest wires, the through holes
26
may be formed in the center portion of the board, not the peripheral portion thereof. In this case, however, dead space where wiring is not possible is formed in the portion where the through holes
26
are formed. Thus, to secure wiring space, the board itself would inevitably become larger.
With regard to another conventional wiring board
60
illustrated in
FIG. 9
, signal lines
62
connected to pads
61
have a given width irrespective of the positions of the signal lines. In this case, it is necessary to set the widths of the signal lines
62
smaller, so that the wiring resistance is likely to increase and line disconnection is apt to occur. This reduces the reliability of the wiring board
60
.
There is a proposed solution to this shortcoming, in which each signal line
62
consists of a first wiring pattern
62
b
with a predetermined width and a second wiring pattern
62
a
having a width greater than that of the first wiring pattern
62
b
, as shown by two-dot chain lines in FIG.
9
. In this case, the first wiring patterns
62
b
are arranged at a high wiring-density portion and the second wiring patterns
62
a
are arranged at a low wiring-density portion to facilitate the wiring and suppress the occurrence of line disconnection.
Since the first wiring pattern
62
b
is directly connected to the associated second wiring pattern
62
a
in this case, two sharp corners are formed at the connected portion. Stress is apt to concentrate on those corners, which raises another problem that cracks
64
are easily formed in a permanent resist
63
near the corners as shown in FIG.
10
.
SUMMARY OF THE INVENTION
With a view to solving the above-mentioned problems, the present invention has been accomplished, and it is a primary objective of the present invention to improve the wiring efficiency while avoiding the enlargement of the entire board. Further, it is another objective of this invention to improve the wiring efficiency while suppressing an increase in the wiring resistance and the occurrence of line disconnection and preventing the occurrence of cracks in a permanent resist.
To achieve the above objectives, a board for mounting electronic circuit parts according to one aspect of this invention comprises:
a first connection terminal group including a plurality of connection terminals densely formed over a top surface of a substrate having through holes formed therein;
a second connection terminal group including a plurality of connection terminals formed at at least a peripheral portion of a back surface of the substrate, the first connection terminal group being connected to the second connection terminal group via the through holes;
a build-up multilayer interconnection layer formed on the top surface of the substrate and including at least one conductor layer and at least one insulator layer alternately stacked one on another,
the at least one insulator layer having a plurality of via holes for electric connection of the at least one conductor layer electrically connected to the through holes; and
wherein the first connection terminal group is formed on an outermost layer of the build-up multilayer interconnection layer.
The first connection terminals are densely formed on the substrate and the second connection terminals are formed discretely. The first connection terminals are connected to the second connection terminals via the via holes as well as the through holes. It is therefore possible to shorten the wires without producing dead space and improve the wiring efficiency. This feature can provide a device which is equipped with electronic circuit parts and has an improved processing speed.
According to another aspect of this invention, there is provided a board for mounting electronic circuit parts, comprising a plurality of connection terminals and a plurality of signal lines formed on an insulator layer. The plurality of connection terminals are formed densely and are respectively connected to said signal lines.
Each of the signal lines include a plurality of wiring patterns with different widths and a taper-shaped pattern connecting said wiring patterns with the different widths so as to have a continuously changing width. Each of the signal lines has a smaller width at an area having a relatively high wiring density than at an area having a relatively low wiring density.
Since each signal line is so formed that it has a smaller width at an area having a relatively high wiring density than at an area having a relatively low wiring density, it is possible to form a wiring pattern having narrow line widths in the high wiring density area and having wide line widths in the low wiring density area. This suppresses the resistance and prevents line disconnection. It is also possible to secure the insulation between patterns in the high wiring density area.
Because wiring patterns with different widths can be connected by the taper-shaped pattern, insulation between signal lines can be secured without causing cracks in the permanent resist and the wiring resistance is not increased.
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pate
Asai Motoo
Kawamura Yoichiro
Mori Yoji
Gaffin Jeffrey
Ibiden Co. Ltd
Madson & Metcalf
Norris Jeremy
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