the cause of the low shearing strength

Abnormal shearing strength of solderball

It`s important to insure the enough shearing strength of solderball. We have done EDXA of the failure samples, We can know the major element is the carbon and Al on the bonding area, carbon was 60 precent.
In order to know the source of the carbon, we have done EDXA of meterial having contanted with the surface of the die. The result show the blue film contains 60 percent .
Then we have cleaned the surface of samples and found the contents becoming lower to several percent.