Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2000-07-12
2002-03-19
Picardat, Kevin M. (Department: 2823)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C438S106000, C438S121000
Reexamination Certificate
active
06358779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor manufacturing, and, in particular, to a technique for reducing dambar burrs on semiconductor devices.
2. Description of the Related Art
Leads for surface-mount semiconductor devices are fabricated in a frame with a portion—known as a dambar—that must be subsequently removed.
FIG. 1
shows a cutting die for dedam/dejunk die set, which is typically used to remove the dambar. As shown in
FIG. 1
, a dedam/dejunk die set generally comprises a cutting insert
102
, mounted, with a mounting screw
104
, within a pocket
106
of a holding plate
108
, and a punch (not shown). The cutting insert has a cutting edge
110
and a screw clearance
112
in its edge opposite the cutting edge. Holding plate
108
has a screw clearance
114
surrounding a threaded hole
116
.
After placing cutting insert
102
within pocket
106
of holding plate
108
, mounting screw
104
is inserted through screw clearances
112
and
114
and fastened into threaded hole
116
in mounting plate
108
to secure the cutting insert in place. In particular, the head of mounting screw
104
presses against the bottom of screw clearance
112
in cutting insert
102
, restraining movement of cutting insert
102
. To sever the dambar from each lead, the dambars are pinched between cutting edge
110
of cutting insert
102
and the punch.
The clearance between the cutting edge of the cutting insert and the punch is preferably between about 5% and 9% of the lead frame thickness (e.g., about 0.008 mm in one embodiment). When the clearance between the cutting insert and the punch is too great, a small portion of the lead frame may wrap around the cutting insert before the lead frame is severed, causing a dambar burr. Dambar burrs can cause alignment and soldering reliability problems when the surface-mount semiconductor device is installed. Removing dambar burrs requires additional processing and inspection time, increasing cost and reducing process throughput.
Referring again to
FIG. 1
, over a period of use, pocket
106
in holding plate
108
can become worn, causing an increased clearance between cutting insert
102
and holding plate
108
. In that case, the clockwise tightening action of mounting screw
104
restraining cutting insert
102
relative to holding plate
108
can cause the cutting insert to shift laterally to the right, as shown in the top view of FIG.
2
. This shift of the cutting insert can cause an increase in the clearance between the cutting insert and the punch, increasing the likelihood of dambar burrs.
SUMMARY OF THE INVENTION
The present invention provides a technique for reducing dambar burrs formed by a die set having a cutting insert fastened by a mounting screw into the pocket of a holding plate. According to the present invention, the pocket and the cutting insert are configured to receive a clamping plate that inhibits the cutting insert from moving when the cutting insert is secured within the pocket of the holding plate by a mounting screw. In one implementation, the shape of the clamping plate is defined by two intersecting circular arcs of different diameter, where the smaller arc matches the screw clearance in the cutting insert, and the larger arc matches the pocket of the holding plate. The clamping plate is fastened to the holding plate with the smaller arc abutting the screw clearance in the cutting insert and the larger arc abutting the holding plate pocket. In this way, the clamping plate inhibits movement of the cutting insert, when the mounting screw is tightened.
In one embodiment, the present invention is an apparatus for mounting a cutting insert of a die set, wherein the cutting insert has a screw clearance, comprising (a) a holding plate defining a pocket configured to receive the cutting insert; and (b) a clamping plate configured to fit within the pocket of the holding plate and within the screw clearance of the cutting insert, after the cutting insert is inserted into the pocket of the holding plate, to inhibit lateral motion of the cutting insert within the pocket of the holding plate when a mounting screw is inserted through a through hole in the clamping plate and tightened into a corresponding threaded hole in the holding plate.
In another embodiment, the present invention is a method for cutting dambars from semiconductor devices, comprising the steps of (a) placing a semiconductor device having one or more dambars into a die set; and (b) cutting the one or more dambars with a cutting edge of a cutting insert of the die set, wherein the cutting insert is secured within a pocket of a holding plate of the die set using a mounting screw and a clamping plate that inhibits lateral motion of the cutting insert within the pocket when the mounting screw is tightened within a threaded hole in the holding plate.
REFERENCES:
patent: 5753532 (1998-05-01), Sim
Agere Systems Guardian Corp.
Collins D. M.
Mendelsohn Steve
Picardat Kevin M.
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