Metal fusion bonding – Process – With condition responsive – program – or timing control
Reexamination Certificate
1998-10-01
2001-06-26
Heinrich, Samuel M. (Department: 1725)
Metal fusion bonding
Process
With condition responsive, program, or timing control
C228S180500, C382S151000
Reexamination Certificate
active
06250534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire bonding method and apparatus and more particularly to a wire bonding method and apparatus which are used when bonding point coordinates are registered and corrected.
2. Prior Art
FIG. 4
shows one of typical semiconductor devices. In this semiconductor device, pellets
1
are mounted on lead frames
2
, and pads
1
a
1
on the pellets
1
are connected to leads
2
a
1
on the lead frames
2
by means of wires
3
a
1
.
FIG. 5
shows the designations of respective pads, leads and wires to which symbols indicating the bonding order have been assigned. In the following description, pads
1
a
1
,
1
a
2
. . .
1
a
14
will be referred to in general as
1
a
n, leads
2
a
1
,
2
a
2
. . .
2
a
14
will be referred to in general as
2
a
n, and wires
3
a
1
,
3
a
2
. . .
3
a
14
referred to in general as
3
a
n. In other words, pads
1
a
n and leads
2
a
n are connected by means of wires
3
a
n.
The wire bonding apparatus which connects the wires
3
a
n is constructed as shown in FIG.
6
.
A bonding head
8
is mounted on an XY table
7
which is driven in the X and Y directions by an X-axis motor
5
and a Y-axis motor
6
. A bonding arm
9
is installed on this bonding head
8
so as to move upward and downward or pivot. The bonding arm
9
is moved upward and downward or caused to pivot by a Z-axis motor (not shown). A bonding tool
10
is fastened to the tip end of the bonding arm
9
, and a wire (not shown) is passed through this bonding tool
10
. Furthermore, a camera holding part
11
is fastened to the bonding head
8
, and a camera
12
is attached to the tip end of the camera holding part
11
so as to be offset from the bonding tool
10
. The workpieces
13
to which wires are connected are fed to the bonding position by a frame feeder
14
.
In order to perform bonding using the wire bonding apparatus as described above, it is necessary to register the bonding coordinates beforehand. In the registration of the bonding coordinates, a standard pattern which is used for workpiece alignment is first stored in memory, and positions which are used to store this pattern in memory are registered as fixed points. Afterward, the registration of bonding coordinates is performed. Generally, in semiconductor devices of the type shown in
FIG. 4
, the relative positional relationship of the respective pads lan on the pellet
1
is fixed. Furthermore, the relative positional relationship of the respective leads
2
a
n on the lead frame
2
is also fixed. However, since the pellet
1
is fastened to the lead frame
2
by adhesion, the positional relationship between the coordinates on the side of the pellet
1
and the coordinates on the side of the lead frame
2
is usually different in each workpiece
13
.
Generally, the bonding positions of the respective pads
1
a
n can be calculated by detecting the shift from the regular positions of at least two fixed points on the pellet
1
, and the bonding positions of the respective leads
2
is calculated by detecting the shift from the regular positions of at least two fixed points on the lead frame
2
. As a result, bonding is performed in the correct positions of the pads
1
a
n and lead frames
2
a
n. In more complicated semiconductor devices, there may be a detection of positional shifts that use a larger number of fixed points.
An example is described below in which two fixed points on the pellet side and two fixed points on the lead frame side are used. A method that is generally used to perform such an alignment detection of fixed points includes storing a standard pattern of fixed points in memory so that regularizing correlation processing is performed. Naturally, however, other types of detection processing may also be used.
In particular, the registration of fixed points on the side of the pellet
1
is accomplished in the following manner:
Cruciform reticle marks which indicate the center of the camera
12
are displayed on the television monitor (called “monitor”) which shows the images obtained by the camera
12
; a chessman or digital switch which drives the XY table
7
is operated so that the XY table is moved and the camera
12
is positioned above the pellet
1
, and the chessman or digital switch is then operated (while the monitor is viewed by the operator) so that the center of the reticle marks on the monitor is aligned with the desired point. Then, a registration switch is pressed, thus causing the coordinates of the XY table
7
to be registered in the bonding point coordinate memory as a first fixed point. At the same time, the standard pattern of this fixed point is registered in the fixed point standard pattern storage memory. By using a similar operation, a separate point on the pellet
1
is registered as a second fixed point. Incidentally, two separated positions at opposite corners are selected as these fixed points. Fixed points on the side of the lead frame
2
are also registered by means of a similar operation.
After the fixed points are registered, the bonding point coordinates are then registered. As in the case described above, this registration of bonding point coordinates is accomplished in the following manner:
The chessman or digital switch is operated so that the XY table
7
is moved, thus causing the camera
12
to be positioned above the pad
1
a
n or lead
2
a
n that is to be bonded. Then, while viewing the monitor, the operator operates the chessman or digital switch so that the center of the reticle marks on the monitor is aligned with the desired position of the pad
1
a
n or lead
2
a
n. Next, the registration switch is pressed so that the coordinates of the XY table
7
are registered in the bonding point coordinate memory as bonding coordinates. This operation is performed for all of the bonding points, so that the respective bonding point coordinates are registered in the bonding point coordinate memory. Generally, the desired bonding positions are set at the centers of the pads
1
a
n and leads
2
a
n.
By thus registering the coordinates of two fixed points on the side of the pellet
1
, two fixed points on the side of the lead frame
2
and the respective bonding points, it is possible to detect any shift of the fixed points in subsequent workpieces
13
of the same type that are to be bonded. Accordingly, the bonding point coordinates can be automatically corrected so that wire bonding can be performed automatically. In other words, the camera
12
is moved to points above the regular fixed points that have been registered beforehand so that any positional shift of the actual fixed points from the regular fixed points is detected. Then, the actual bonding point coordinates of the respective bonding points are automatically calculated on the basis of these positional shift detection values, and the bonding tool
10
is guided to these corrected bonding points (i. e., the XY table
7
is moved to the respective bonding point coordinates), so that the bonding work is performed automatically.
Actual bonding work is accomplished by moving the XY table
7
to coordinates obtained by adding the amount of offset between the center of the camera
12
and the center of the bonding tool
10
to the respective bonding point coordinates that have been corrected for the positional shift, so that the bonding tool
10
is brought to the respective bonding points. The wire bonding methods and apparatuses of this type are disclosed in, for instance, Japanese Patent Application Publication (Kokoku) Nos. 57-11498, 57-33852, 57-50059 and 61-6541.
Conventionally, in order to determine the positions of the bonding points after the coordinates of the fixed points and bonding points have been registered, the following method has been employed:
The XY table
7
is moved to the position of the stored bonding point coordinates, after which the pad
1
an or lead
2
a
n and the reticle marks shown on the monitor are examined, and a determination is made to see if there is any positional shift in the bonding point.
H
Heinrich Samuel M.
Kabushiki Kaisha Shinkawa
Koda & Androlia
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