Investigation of LowK WLCSP Die Strength Impact induced by Singulation Process

55nm Low-K WLCSP die strength was investigated by new LTCPI (low temperature cured polyimide) material and stealth dicing process. Laser grooving induced HAZ (heat affected zone) size vs. die strength was studied. In this study, a 55nm test vehicle with Low-K intermetal dielectric and WLCSP package build with two different materials, mainly PBO and LTCPI, were processed by standard one RDL layer WLCSP process. Total four die singulation process techniques were evaluated. The experiment results showed laser grooving + blade saw split with over 20% die strength degradation compared with blade saw split. Stealth dicing split was observed with less strength decrease, ~5%. Based on the test results, WLCSP die strength degradation was strongly dominated by HAZ size. WLCSP with PBO and LTCPI material showed comparable die strength by stealth dicing. Based on this study, for LowK WLCSP with large die size products, using stealth dicing singulation process is desired to minimize die strength loss by laser grooving and more stable than blade saw split. The results of this work provide a good reference for WLCSP package singulation process optimization. (Abstract)