Package & board level reliability study of 0.35mm fine pitch wafer level package

Abstract

0.35mm fine pitch wafer level chip scale package (WLCSP) has been developed by NCAP for portable electronic applications. It can provide 196 pin counts in 5mm × 5mm package body size. This paper reports the development work of WLCSP and the package level and board level reliability study including thermal cycling and drop test. The technology is evaluated using a 5mm × 5mm test vehicle with 0.35mm pitch 14×14 full array solder balls. WLCSP TV is fabricated on 300mm diameter wafer. Finite element modeling (FEM) is carried out and the result is compared with experimental data. In the package level reliability study, there is no PI crack or electrical open/short failure after reliability test. In the board level thermal cycling test, the 0.35mm fine pitch WLCSP can pass 300 cycles without underfill protection. In addition to TC test, board level drop test is also evaluated. Drop test board is designed following JEDEC standard JESD22A-112B. PCB thickness is 1.0mm. Cu pad size is 0.28mm and it structure is solder mask defined (SMD) with OSP surface finish. In the drop test without underfill, the first failure is 42 cycles and a characteristic lifetime is 95 cycles. 0.35mm fine pitch WLCSP shows robust structure in both package and board level reliability tests.