Reliability Improvement Study of a Build-up Wire Bonding EBGA Package Using Eight-layer 0.13 um Copper Silicon Technology

Abstract

In this paper, the authors will discuss the die cracking/thin film delamination failures seen in 8-layer 0.13 um silicon during the development of an EBGA package with 45 mm x 45 mm body size. The die size was 15.2 mm per side with over 1400 wire bonded pads. The large package body size and die size provided both manufacturing and reliability challenges.It was pointed out that, due to the large die size and complex 8-layer metal silicon process used, the reliability performance heavily relies on the optimization of the wafer sawing process, stress distributed on the silicon, thin film adhesion, test conditions and assembly variations.Failure analysis demonstrated that cracks initiated from the die edge and then propagated through the interface of M1/silicon interfaces, at certain point, the cracks will turn to the surface shown as die cracking. The experimental result showed optimized dual step cut wafer sawing can significantly reduce the risks of die cracking/thin film delamination, the failure rate can be reduced from ~30% to ~5%. It was also observed that units from various lots are performing significantly different during the reliability testing.Finite element study also showed low stress encapsulation materials will help reduce the tensile stress applied on the die edge, and reduce the risk for die cracking.In the future, additional research will be carried out to understand if the metal density in the scribe is playing a significant role, how the cracks initiated and propagated at what steps.