SMTA International Conference Proceedings

Comparing LGA And BGA Assemblies In Terms Of Solder Pad Cratering

Authors: Y. Zeng, Pericles Kondos, J. Jiang, Martin Anselm and Peter Borgesen
Company: Binghamton University and Universal Instruments Corporation
Date Published: 10/13/2013   Conference: SMTA International

Abstract: Land Grid Array (LGA) packages are attractive for a number of reasons. Unlike with SnPb solder, recent work showed lead free LGA assemblies to survive at least as long as corresponding Ball Grid Array (BGA) assemblies in thermal cycling, in spite of the much shorter solder joints [1]. The superior thermal fatigue resistance of the smaller solder joints was found to be associated with a change in Sn grain morphology in the SAC305 joints, and work is ongoing to determine materials and design parameters that might ensure the reproducibility of this microstructure. On the other hand, the greater rigidity of the shorter joints raises concerns with respect to solder pad cratering, a failure mode that is increasingly dominant under various isothermal loading conditions and is even becoming more common in thermal cycling. The risk of pad cratering increases further because of the greater hardness due to the aforementioned difference in morphology which adds further to the already high stiffness of the joints. Nevertheless, cyclic bending experiments showed delayed cratering in LGA assemblies compared to BGA assemblies [1].

The question remains as to how general this result is when design, materials, and loading parameters are varied. This is the focus of the present paper.

Key Words: 

Pad Cratering, Land Grid Array (LGA), Ball Grid Array (BGA), Life Dependence, Creep, Four Point Bending, Hot Bump Pull

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