Drop impact life prediction model for lead-free BGA packages and modules

System-in-package (SiP) such as multi-chip or stacked die BGA modules with wirebond, flip-chip or hybrid interconnect are getting popular for advanced packaging applications. The design of SiP is more dependent on modeling as the package structure and failure mechanism are too complicated to be studied. It is known that drop impact reliability of lead-free BGA solder joints is a critical challenge. Drop impact life of IC packages mounted on board becomes a hot topic, especially for design and qualification of handheld electronic products. Actual drop test and sample preparation are very expensive and time-consuming, requiring much manpower in measurement and failure analysis, and therefore, there are limited drop test results reported to advise on the package design enhancement, especially for lead-free packages. In this paper, various design parameters are studied experimentally and numerically, to understand the effects of ball height, ball size, and ball layout. A thorough understanding of design variables on impact life of IC packages are obtained based on such well-designed and controlled experiments. On the other hand, more that 10 BGA packages with different package size, ball layout, package layout, and die thickness are tested with well-controlled drop tester. For the first time, an accurate drop impact life prediction model is established for lead-free (SnAgCu) BGA packages and modules, having good correlation with 16 cases of actual board level drop testing results. This quantitative approach is different from traditional qualitative modeling, as it provides both accurate relative and absolute impact life prediction. The validated model is applied to provide design guidelines for lead'free BGA and modules to improve their drop impact reliability. One point to be noted is that the relative performance of package may be different under board level drop test and thermal cycling test. Therefore, different design guidelines should be considered, depending on application and area of concern.