Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-12-07
2002-10-22
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
82, 82
Reexamination Certificate
active
06467162
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, and also relates to a method for mounting a device on the printed circuit board. 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
01
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
01
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
01
by a distance L
1
and also mounts the device
5
on another position apart from the center
01
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
01
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
01
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
01
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
01
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
01
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.
In a further preferred embodiment, the present invention is directed to a method for mounting devices, by a mounter, on 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, a land being not coated with the resist and a second mark formed by said resist which is coated on the printed circuit board together with said land being partially coated, said method comprising the steps of:
detecting a center of said first mark and a center of said second mark;
mounting a device, which corresponds to said land being partially coated with the resist, at a position apart from said detected center of said second mark by a predetermined distance; and
mounting a device, which corresponds to said land being not coated with the resist, at a position apart from said detected center of said first mark by a predetermined distance.
In a still further preferred embodiment, the present invention is directed to a method for mounting devices, by a mounter, on 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, a land being not coated with the resist and a second mark formed by said resist which is coated on the printed circuit board together with said land being partially coated, said method comprising the steps of:
detecting a center of said first mark and a center of said second mark;
mounting a device, which corresponds to said land being not coated with the resist, at a position apart from said d
Arbes Carl J.
Birch & Stewart Kolasch & Birch, LLP
LandOfFree
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