Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-07-17
2002-04-02
Cuneo, Kamand (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S250000, C174S260000, C361S783000, C361S811000, C361S808000, C361S767000
Reexamination Certificate
active
06365841
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printed circuit board (PCB) including a mark which is used as a recognition of an origin for mounting by a mounter. More specifically, this invention relates to a technique which enables proper mounting of devices, on the printed circuit board, including a land which is partially coated with a resist and a land which is not coated with the resist, even if the resist is coated on the printed circuit board at an improper position.
BACKGROUND
As shown in
FIG. 2
, a mark
2
made of a conductive leaf or a thin conductor is formed on a prior art printed circuit board
10
. When a mounter mounts devices
4
,
5
such as electric parts on the printed circuit board
10
, the mark
2
is recognized and used as an origin for mounting by the mounter. The mounter is a machine which is used for mounting devices on the printed circuit board. In
FIG. 2
, a symbol O
1
denotes a central point of the mark
2
, a symbol
6
′ denotes a land on which the device
4
is mounted, a symbol
7
denotes a land on which the device
5
is mounted, and a symbol
8
denotes a resist material (a solder resist). In
FIG. 2
, there is shown a separation between the outer boundaries of lands
6
′ and
7
, and the respective boundaries of the surrounding resist
8
. In the prior art, the resist
8
is generally coated on the printed circuit board
10
except for the mark
2
, the land
6
′ and the land
7
respectively.
It will be explained how the mounter mounts the devices
4
,
5
on the printed circuit board
10
. For the sake of simplicity, only a position in a horizontal direction X, shown in
FIG. 2
, is considered.
Before mounting the devices
4
,
5
, the mounter detects the center O
1
of the mark
2
from an output of a sensor such as a CCD camera. Then, the mounter mounts the device
4
on a position apart from the center O
1
by a distance L
1
and also mounts the device
5
on another position apart from the center O
1
by a distance L
2
. These distance values L
1
and L
2
are previously registered on a data-base provided with the mounter. The value L
1
is predetermined, by a design-specification for the printed circuit board
10
, as a distance from the center O
1
of the mark
2
to a center of the land
6
′ and the value L
2
is also predetermined, by the design-specification for the printed circuit board
10
, as a distance from the center O
1
of the mark
2
to a center of the land
7
. Therefore, as far as the resist
8
is coated on the printed circuit board
10
except for the the land
6
′ and the land
7
, the devices
4
and
5
are properly mounted on the land
6
′ and the land
7
respectively.
However, as shown FIG.
3
(B), in a case that the resist
8
is partially coated onto the land
6
, a position error of the device
4
occurs in its mounting for following reasons (1)~(6). In this case, for the sake of simplicity, only a position in a horizontal direction X, shown in FIG.
3
(A) or FIG.
3
(B), is considered.
(1) The resist
8
is coated on the printed circuit board
10
, which is already provided with the mark
2
and the lands
6
,
7
, through a mask (not shown) which is put on the board
10
. It is assumed that the mask is formed so as to coat the resist
8
on the land
6
except for its central area
6
A, and so as to avoid the land
7
by a sufficient clearance and avoid the mark
2
by an extremely sufficient clearance from the resist
8
, respectively.
(2) Therefore, if there occurs a few positional errors between the printed circuit board
10
and the mask, a center of the exposed area
6
A, which is not coated with the resist
8
out of the land
6
, shifts from a center of the land
6
itself.
(
3
) FIG.
3
(A) shows a proper relation between the printed circuit board
10
and the mask. In this case, since the center of the exposed area
6
A coincides with the center of the land
6
itself, the center of the exposed area
6
A is located at the distance L
1
apart from the center O
1
of the mark
2
, and the device
4
is properly mounted on the exposed area
6
A of the land
6
.
(4) On the other hand, FIG.
3
(B) shows an improper relation between the printed circuit board
10
and the mask. As shown in FIG.
3
(B), if the resist
8
is coated with a position error &Dgr;L
1
against the printed circuit board
10
, the center of the exposed area
6
A is shifted by &Dgr;L
2
from the center of the land
6
itself. Therefor, since the mounter mounts the device
4
at the distance L
1
from the center O
1
of the mark
2
, the device
4
is not properly mounted on the exposed area
6
A.
(5) Regarding the land
7
, the mask is generally designed so that the minimum gap is assured between the land
7
and the resist
8
, even if the mask is shifted a little against the printed circuit board
10
. In FIG.
3
(B), this minimum gap is illustrated by the left boundaries of the lands
7
being located nearly at the boundary of the resist
8
, while the separation between the right boundaries of the lands
7
and the boundary of the resist
8
has increased relative to FIG.
3
(A). Therefor, the device
5
is properly mounted on the land
7
in spite of the positional error of the resist
8
.
(6) Regarding the mark
2
, the mask is generally designed so that a sufficiently wide gap is assured between the mark
2
and the resist
8
, even if the mask is largely shifted against the printed circuit board
10
. Therefore, the center O
1
of the mark
2
is not shifted by the positional error of the resist
8
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a printed circuit board and a method, each of which enables proper mounting of devices on the printed circuit board having a land which is partially coated with a resist and a land which is not coated with the resist, even if the resist is shifted against the printed circuit board.
In a preferred embodiment, the present invention is directed to a printed circuit board having a first mark which is formed by a thin conductor or a conductive leaf for mounting a device, a land being partially coated with a resist and a land being not coated with the resist, wherein said printed circuit board further comprises a second mark formed by said resist which is coated on the printed circuit board together with said land being partially coated.
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: 3775844 (1973-12-01), Parks
patent: 5512712 (1996-04-01), Iwata et al.
patent: 5912438 (1999-06-01), Kubin
Cuneo Kamand
Fuji Photo Film Co. , Ltd.
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