TABLE II.

Summary of the Visual Inspection on the Failed Bumps of the 3-D Stacks

# of die in the stacks	Failure location	Condition	Details results
1	Ag bump	1st trial – no epoxy	18 bumps are failed: most failures are close to the interface b/w Al pad and Ag bump; some failures are close to the interface b/w Au pads and Ag bump; no failure on the polysilicon; see sample in Fig. 19A
1	Ag bump and poly pads	2nd trial – no epoxy	10 out of 18 bumps are failed on the polysilicon pads - suggesting that this particular die may have a prior fabrication issue which impact its polysilicon strength; 8 bumps are failed on the interface b/w Au pad and Ag bump
1	No failure	Epoxy encapsulation	18 bumps are still intact with no visible issue; the amount of force required to fail the package exceed the ability for the current testing method. 1,000 g
2	Adhesion of Ag and Si surface	1st trial	The failure is on the 2nd die (top). All 18 bumps show same the signature of failure – on the interface b/w Ag bumps and Si-die. Suggesting a poor adhesion b/w Ag and bare Si-surface; the base (1st die) is still attached strongly even though it experiences more magnitude of combination - shear and bending strength; see sample in Fig. 19B
2	Adhesion of Ag and Si surface	2nd trial	The failure is on the 2nd die (top); Same signature as the 1st trial.
2	No failure	Epoxy encapsulation	18 bumps are still intact with no visible issue; the amount of force required to fail the package exceed the ability for the current testing method. 1,000 g
3	Adhesion of Ag and Si surface	1st trial	Failed on the 3rd die, all 18 bumps are showing the same signature of failures, which is at the interface between the Ag bump and the Si bare die (non polished surface); see sample in Fig. 19A
3	Adhesion of Ag and Si surface	2nd trial	Both 2nd and 3rd die are failed, cannot really tell which die that failed first; It is believed that the 3rd die failed first and its impact trigger the 2nd die; Same failure signature as the 1st trial.
3	No failure	Epoxy encapsulation	18 bumps are still intact with no visible issue; the amount of force required to fail the package exceed the ability for the current testing method. 1,000 g = 4 x the weight of adult rat