Metal deforming – With cutting – By composite tool
Reexamination Certificate
1999-07-13
2001-08-21
Crane, Daniel C. (Department: 3725)
Metal deforming
With cutting
By composite tool
C072S450000, C029S566300, C074S045000
Reexamination Certificate
active
06276184
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for manufacturing semiconductor devices comprising a die on a carrier, the process comprising the steps of
providing the carrier,
stamping the carrier with a stamping tool by driving the stamping tool in a reciprocating manner in a stamping direction by means of a conversion mechanism which converts a rotary movement to a reciprocating movement.
The invention further relates to an apparatus for manufacturing semiconductor devices comprising a die on a carrier, the apparatus comprising
a chassis,
a plunger for carrying a stamping tool, which plunger is guided relative to the chassis in a stamping direction by a plunger bearing,
a conversion mechanism for driving the plunger in a reciprocating manner in the stamping direction, the conversion mechanism being conceived to convert a rotary movement to a reciprocating movement. Here the word ‘stamping’ is meant to include processes such as IC damber cutting, trim forming and BGA singulation by means of punching.
Such a process and such an apparatus are known from U.S. Pat. No. 5,493,768. The known apparatus comprises a motor driven disc and a rod that is eccentrically connected with one end to the disc. The other end of the rod is connected to a first end of a horizontal lever. The horizontal lever is rotatably connected to a chassis and is connected at a second end to a plunger via a plunger rod. When the disc is rotated the lever is tilted via the rod and the plunger is reciprocally driven in the horizontal direction. A stamping tool can be connected to the plunger in order to trim excess portions from leads of a leadframe strip package having a semiconductor chip mounted thereon. It has been found that stamping with the known apparatus does not always result in semiconductor devices that meet the dimensional tolerance requirement of the leads such as coplanarity.
SUMMARY OF THE INVENTION
It is an object of the invention to improve the coplanarity of semiconductor devices. It is another object of the invention to increase the lifetime of the stamping tool.
The process according to the invention is characterised in that during stamping of the carrier substantially no force is exerted by the conversion mechanism on the stamping tool in directions perpendicular to the stamping direction. The invention is based on the insight that the conversion mechanism which is used in the known process results in a resultant force component on the stamping tool in a direction perpendicular to the stamping direction and that the direction of this resultant force component changes when the direction of the movement of the stamping tool changes. This changing resultant force component in a direction perpendicular to the stamping direction causes the stamping tool to make a tilting movement superpositioned on the movement in the stamping direction. Due to this tilting the co-planarity of the semiconductor device is affected. Due to the measure according to the invention, the stamping tool does not tilt during stamping of the carrier so that the co-planarity of semiconductor devices manufactured with this process is improved in comparison with the known process.
Mounting the die on the carrier before stamping the carrier has the advantage that the carrier can be handled more easily during mounting of the die because it can be part of a strip or an array of carriers. It can be provided with positioning elements and the carrier can be separated from the strip, array and/or positioning elements by means of stamping after mounting of the die.
Encapsulating the die before stamping the carrier has the advantage that the carrier can be dimensioned and/or trimmed as a last step in the production process so that the dimensional tolerances of the carrier can be minimised.
Biasing the stamping tool in a direction parallel to the stamping direction has the advantage that any play in the mechanism for moving the stamping tool is neutralised so that this play does not affect the dimensional tolerances of the carrier.
The apparatus according to the invention is characterised in that the conversion mechanism is conceived to exert substantially no force on the plunger in directions perpendicular to the stamping direction. Due to this measure the advantages of the process according to the invention are obtained. Another advantage of this measure is that the plunger bearing does not have to absorb large tilt forces. As a result, the wear of the plunger bearing is reduced and the stamping tool remains accurately positioned even after a large number of strokes so that a more constant quality of the semiconductor devices is obtained.
A lever can very suitably be used in a conversion mechanism for converting a rotational movement to a reciprocating movement because it can amplify a force. That has have the advantage that there is substantially no resultant force on the lever in a direction perpendicular to the stamping direction during stamping. As a result, the lever will not exert any force on the plunger and the stamping tool in a direction perpendicular to the stamping direction.
An advantage is that a slide coupling reduces the forces in the slide direction to the residual friction forces in the slide coupling so that almost no forces in the transversal direction are exerted on the lever.
An advantage is that there is virtually no resultant force on the lever in a direction perpendicular to the stamping direction, while the use of expensive slide couplings is avoided. The first coupling exerts a first force in the transverse direction and the second coupling exerts a second force in the transverse direction, which first force and second force are of substantially equal magnitude and opposite in direction so that the forces in the transverse direction on the lever are balanced.
An advantage is that any residual transverse force on the lever is absorbed by the lever bearing and is not transferred to the stamping tool.
An advantage is that the play in the couplings is neutralised so that this play does not affect the position of the stamping tool.
REFERENCES:
patent: 629392 (1899-07-01), Protheroe
patent: 1363021 (1920-12-01), Slee
patent: 4318325 (1982-03-01), Bareis
patent: 4335497 (1982-06-01), Casey
patent: 4419929 (1983-12-01), Dommer
patent: 5493768 (1996-02-01), Fierkens
patent: 2045154 (1980-10-01), None
Crane Daniel C.
U.S. Philips Corporation
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