Pan Pacific Symposium Conference Proceedings


USING UNDERFILLS TO ENHANCE DROP TEST RELIABILITY OF Pb-FREE SOLDER JOINTS IN ADVANCED CHIP SCALE PACKAGES

Authors: Brian Toleno, Ph.D., Dan Maslyk, and Tom White
Company: Henkel Corporation
Date Published: 1/31/2007   Conference: Pan Pacific Symposium


Abstract: With the RoHS deadline now behind us, one would assume that most issues pertaining to lead-free manufacturing would be resolved by now. Manufacturers have tested and re-tested materials, evaluated various process parameters and many have already implemented full Pb-free manufacturing. There are, however, questions that remain regarding the reliability of the SAC (Sn-Ag-Cu) alloys as compared to SnPb alloys [1]. By nature, lead-free solder joints are more brittle than their SnPb predecessors [2]. Lead-free solder joints have an increased tendency to crack and break, especially when subjected to external forces such as dropping because of this brittleness. In today’s mobile phones, PDAs, iPods™ and the plethora of other mobile communication devices, this is precisely what happens. Couple this with the fact that these devices are populated with very fine pitch, increased functionality CSP devices which, as mentioned previously, have challenges in a lead-free manufacturing environment, and it would appear that Pb-free solder joint failures in these products is inevitable. Even though there are a variety of SAC alloys being used in the industry testing has showed that the reliability and processing of these alloys can be considered to be equivalent [3]. Some of the issues related to unexpected Pb-free solder joint failures have been studied and addressed. Just as underfill materials have provided stability to CSP devices for failures arising from higher temperature lead-free processing requirements, new testing has recently revealed that certain types of underfills also provide protection against failure during board flexure from drop test. In this paper we compare the reliability of two different sized area array components: 0.4mm pitch wafer level chip scale packages (WLCSP) and 0.5 mm pitch chip scale package (CSP). The reliability of these devices, in both Sn/Pb and lead-free assemblies are evaluated using industry standard drop test methodology. The improvement of the reliability of these devices thorough the use of underfill systems is also demonstrated. Key words: underfill, reliability, WLCSP, drop testing



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