Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-06-30
2001-04-17
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
Reexamination Certificate
active
06218630
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printed circuit board suitable for mounting parts, which has many ball-type terminals arranged in a plurality rows with a narrow pitch.
BACKGROUND DESCRIPTION
As a shape of terminal formed on an IC (Integrated Circuit), a pin-type or lead-type terminal and a ball-type or bump-type terminal are known. An IC having pin-type terminals arranged in a row is known as a PGA (Pin Grid Array). An IC having ball-type terminals arranged in a row is known as a BGA (Ball Grid Array).
The BGA is more suitable for a high-density mounting than the PGA for the following reasons.
(1) It is possible to narrow a pitch between the terminals. As a result, it is possible to make a small-sized IC which has many ball-type terminals.
(2) It is not necessary to make a hole in a land of a printed circuit board, wherein ball-type terminals are not passed through the hole. As a result, it is possible to make a small-sized land. Further, it is possible to narrow a pitch between the lands.
FIG. 8
shows a side view of a printed circuit board
70
on which the BGA
60
is mounted. The BGA
60
has an array of the ball-type terminals
61
. Then, corresponding to the arrays of the ball-type terminals
61
, an array of the lands
71
is formed on the printed circuit board
70
. Each ball-type terminal
61
is connected with each land
71
by the solder
80
.
The BGA, of which terminals are arrayed in a row with a narrower pitch than
0
.
8
mm, is known as a CSP (Chip Size Package) because a package-size of the BGA is close to a size of a chip inside the BGA package.
However, in a case that a pitch between terminals is about
0
.
5
mm and the CSP has two arrays respectively arranged in an inner row and in an outer row, it is technically impossible to mount the CSP on a printed circuit board for the following reasons (1)~(4).
(1) The printed circuit board
70
shown in
FIG. 9
is considered in this discussion. On the printed circuit board
70
, with a pitch of 0.5 mm, an array of inner lands
72
of a circular shape and an array of outer lands
73
, also of a circular shape, are formed. Further, on the printed circuit board
70
, a pattern
74
from the inner land
72
is passed through a gap between the outer lands
73
.
(2) In the prior art, a diameter of the outer land
73
is 0.4 mm and a diameter of the inner land
72
is also 0.4 mm.
(3) If the width of the pattern
74
is 150 &mgr;m, which is generally used, it is impossible for the pattern
74
to pass through the gap between the outer terminals
73
because the gap is 0.1 mm (=0.5−0.4=100 &mgr;m).
(4) Further, if the width of the pattern
74
is 50 &mgr;m, which is the minimum for practical use, it is also impossible for the pattern
74
to pass through the gap between the outer terminals
73
because a gap between the the pattern
74
and the adjacent outer terminal
73
is typically 25 &mgr;m (=(100−50)/2).
On the other hand, it is considered to draw the pattern
74
from the inner land
72
via a thru-hole which is formed in a area
75
surrounded by the array of the inner lands
72
. However, in the case of CSP, extremely small thru-holes are necessary for this purpose because the area
75
is very small and many patterns
74
are formed. Since such a small thru-hole cannot be formed by usual multi-layer techniques, the printed circuit board becomes very expensive. Thus, it is not practical to use such a thru-hole.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a printed circuit board suitable for mounting parts, which has a plurality of arrays of ball-type terminals with a narrow pitch.
In a preferred embodiment, the present invention is directed to a printed circuit board for mounting parts, which has a plurality of arrays of ball-type terminals arranged inside and outside of one another, said printed circuit board comprising:
a plurality of arrays of lands arranged relatively inside and outside of one another, formed corresponding to said arrays of ball-type terminals; and
a pattern, originating from an inner land and continuing between two outer lands, wherein
a size of an outer land, in a direction along an outside array is smaller than a size of an inner land in a direction along an inside array.
In a further preferred embodiment, a size of the outer land in a direction perpendicular to the direction of the outside array is larger than the size of the outer land in the direction along the outside array.
In a still further preferred embodiment, the size of the outer land along the direction of the outside array is equal to or smaller than 0.15 mm, a pitch of the inner lands is equal to or smaller than 0.5 mm and a pitch of the outer lands is equal to or smaller than 0.5 mm.
In another preferred embodiment, a pattern is connected with an outer land and a width of the pattern is gradually widened in a connected area between the outer land and the pattern.
In yet a further preferred embodiment, a pattern is connected with an inner land and a width of the pattern is gradually widened in a connected area between the inner land and the pattern.
In an even further preferred embodiment, a resist or a solder resist is coated, around the outer land, from an outer area to an inner area of the outer land.
In yet an even further preferred embodiment, the resist is coated, around the inner land, from an outer area to an inner area of the inner land.
These and other objects of the present application will become more readily apparent from the detailed description given hereafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4600970 (1986-07-01), Bauer
patent: 5285352 (1994-02-01), Pastpre et al.
patent: 5547740 (1996-08-01), Higdon et al.
patent: 5585162 (1996-12-01), Schueller
patent: 5641946 (1997-06-01), Shim
patent: 5869887 (1999-02-01), Urushima
patent: 5885476 (1999-03-01), Hong et al.
patent: 5906042 (1999-05-01), Lan et al.
patent: 5977641 (1999-11-01), Takahashi et al.
patent: 5982033 (1999-11-01), Ohsawa et al.
patent: 5982186 (1999-11-01), Buschbom
Fuji Photo Film Co. , Ltd.
Gaffin Jeffrey
Norris Jeremy
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