Board level reliability study for CSP with 400 um ball pitch

Abstract

For handheld products, drop impact is a great concern to simulate mishandling during usage. The primary driving force of the electrical failure is rapidly winding of circuit board due to high-accelerated strain. Therefore, the board level drop test is created to go through the performance of dropping the handheld electronic product. At the present days, Sn1Ag0.5Cu solder ball is adopted for thin and fine pitch ball grid array (TFBGA) with 500 mum ball pitch, and the performance of solder joint in this scale is robust enough for shouldering the survey under the board level drop test and temperature cycling test. However, as the dimension of integrated circuit device much narrower, the ball pitch must be compelled to lessen from 500 um to 400 um, and the capability of solder joint will be challenged in the board level drop test and temperature cycling test. In this study, we reconsider the capability of solder joint with different compositions of solder balls onto Ni/Au surface finish, including Sn1.0Ag0.5Cu, Sn2.6Ag0.6Cu and Sn3.0Ag0.5Cu. Moreover, two solder mask openings (SRO), 250 mum and 200 mum, are selected and land grid array (LGA) structure is used to compare with normal BGA one. The assessments of the distinct types of TFBGA and LGA components are gauged by standard reliability tests, such as JEDEC board level drop test and IPC TCT solder joint reliability test. While the standard reliability test done, we make use of the universal statistics of Weibull failure analysis to estimate the robust degree of the performance. The result showed that the solder ball of Sn1.0Ag0.5Cu has better performance than others composition ones by board level drop test and the 250mum SRO caused superior board level drop reliability than 200mum ones. Additionally, LGA structure with low standoff height (~50mum) also revealed better drop test reliability than normal BGA (~85mum) due to lower stress. In conclusion, compared to 0.5mm ball pitch result, all groups showed acceptable solder joint reliability and Sn3.0Ag0.5Cu showed better performance than others.