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Stitch Bond Reliability

The wire bond pull testing has been an acceptable method in the semiconductor industry to determine the bond quality in terms of pull strengths typically expressed in grams. Generally, the bonded wires are pulled at the highest loop or 1/3 distance from the ball bond and the readings are taken. However, this method does not prove to be effective due to the nature of application wherein low loop and long wires are used. This has led into some misleading pull test results due to the differences in bonded wire lead lengths.

One practical application of the pull test is to determine the actual break load of the wire and its mode of failure closer to the stitch as possible. This means that the pull tester hook must be placed in such a way that it would not interfere with the other wire and then the wires are pulled. The actual gram gauge reading and more importantly, the mode of failure are then taken.
Wire bond pull testing



The challenge here is how close the hook can be positioned perpendicular to the stitch being pulled, considering the wire diameter of the hook, and how it is being pulled. The gram gauge readings, mode of failure, and the residual of the tail left after it has been pulled. Most importantly, there must be no lifted stitch. Visual appearance of the stitch is also essential to detect if there is a serious cut stitch or tearing problem. Potentially, this would give lower stitch pull readings.
 
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