Design for Improvement of Drop Impact Performance of IC Packages

Solder joint reliability of IC packages under drop impact becomes a great concern for portable telecommunication devices such as mobile phones and PDAs. It is known that drop impact reliability of lead-free BGA solder joints is a critical challenge. With the development of advanced packaging applications such as system-in-package (SiP), package on package (PoP), embedded die, stacked die BGA, etc, package design is more dependent on modeling as the package structure and failure mechanism are too complicated to be studied. 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. To avoid long cycle time for package development and expensive reliability testing, design for reliability is necessary in package early design stage. In this paper, various design parameters are studied to understand the effects of solder material, molding compound, substrate, solder mask opening, ball layout, enhancement ball, etc based on a good drop impact model developed in our previous work. A thorough understanding of design variables on impact life of IC packages is obtained. Some factors have significant effects on drop impact life. It is very useful for designer to design a reliable package with such design considerations and guidelines. 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.