Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-08-02
2001-01-09
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192160, C204S192220, C204S192230, C427S569000, C427S523000, C427S530000, C427S577000, C427S578000, C427S579000, C427S585000, C427S902000, C427S906000, C228S004500, C228S054000
Reexamination Certificate
active
06171456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bonding tools of the type used in automatic wire bonding machines and tape automated bonding machines to make electrically conductive interconnections between the pads on a semiconductor device and the leads on a frame or carrier. More particularly, the present invention relates to adding a very thin hard coating of amorphous ceramic material to the working face of known bonding tools so that the original specifications and tolerances are preserved and the working face is improved in smoothness and hardness.
2. Description of the Prior Art
Bonding tools used to make fine wire interconnection on semiconductor devices are commercially produced as capillary bonding tools or as wedge bonding tools. By far the larger percentage of such tools are capillary bonding tools. Either type tool may be modified to produce a single point bonding tool of the type used to connect a prefabricated flexible pattern of leads to pads on a semiconductor device in a process called the tape automated bonding or TAB. Each of the three types of tools have been made in more than one type of working face in order to solve different problems.
A current problem is excessive wear of the working face of each bonding tool used for very small bonding pads on a semiconductor device. The pads are presently smaller than 3.0 mils square on high density computer chips of the type which typically drive the state of the art. The next generation computer chip will have 2.0 mil square pads. The bonding tools used to make wire bonds or TAB bonds on these pads must have a working face that does not extrude or expand the bond being made over the edges the pads. This requires that the tip diameter (T) of the fine pitch bonding tool be made about the size of the pad and that the working face which extrudes the fine pitch wire or tab lead be effectively smaller that than the pad size or under 3.0 mils.
The above requirements, when imposed on fine pitch bonding tools have resulted in smaller working faces on high speed bonding tools of the type shown and described in U.S. Pat. Nos. 5,421,503 and 5,558,270 that are assigned to the assignee of the present invention. It was found that the mean time before replacement of these prior art tools has been reduced by over 50% and the next generation of fine pitch bonding tools will have a further reduced operational life.
It would be desirable to provide capillary or wedge type bonding tools which can be made on existing production machinery using existing materials and methods of manufacture that can be further processed in a manner which more than doubles the operational life of the bonding tool.
SUMMARY OF INVENTION
It is a principal object of the present invention to provide a new and improved longer lasting bonding tool than existed heretofore.
It is another principal object of the present invention to provide a method of making a long lasting bonding tool without changing the tolerance dimensions of the prior art tools.
It is another object of the present invention to employ an inherent high temperature post operative sputtering step for coating a thin hard layer of glass like ceramic material onto a bonding tool while controlling the surface temperature of the bonding tool being coated.
It is another object of the present invention to limit the deposition of a ceramic coating being applied to a bonding tool to a desired predetermined working face area.
It is another object of the present invention to provide a novel method of substantially increasing the hardness of the working face of a bonding tool without affecting the size or hardness of the remainder of the bonding tool.
It is another object of the present invention to provide a novel method of selectively hardening portions of the bonding tool to increase the working life in production.
According to these and other objects of the present invention there is provided a microminiature fine pitch bonding tool having a working face width or thickness less than four mils across and having tolerances limited to fractions of a mil. A thin hard layer of ceramic material is sputtered onto the working face of the bonding tool at a controlled temperature between 200° to 800° centigrade to deposit a layer less than one micron in thickness which increases the hardness by about fifty percent and increases the useful life by about one order of magnitude.
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Hadar Ilan
Sonnenreich Beni
Diamond Alan
Kulicke and Soffa Industries Inc.
Sowell-Aty John B.
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