Investigation of Production Quality and Reliability Risk of ELK Wafer WLCSP Package

WLCSP has been widely adopted for package solution of the portable and wearable electronics products by its advantages of very low package cost and good electrical performance. Knowing WLCSP provide almost no protection to silicon IC chip, its quality and reliability performance becomes critical for successful product application. A 28nm TV with extreme Low-k inter-metal-dielectic material (ELK IMD) and 4×4mm2 chip size was used for WLCSP production quality investigation by studying the impact of laser grooving, used in WLCSP process, on silicon crack resistance. Four different laser grooving splits DOE were performed including different power, speed and frequency. A hammer test by 2-meter height single-reel drop and 3-point bending test were conducted to assess the silicon crack resistance performance of each split. The test results showed the split with low laser power and low unit length area power density achieved higher die strength by higher 3point bending force and higher silicon crack resistance by more single-reel-drop counts without silicon chipping defect. Moreover, tape-and-reel (TnR) pocket design impact on WLCSP silicon crack defect also was evaluated. With small chip-pocket tolerance design, <;= 0.25mm, the single-reel drop test result was improved without chip edge silicon crack.