LORD SolderBrace? Wafer Applied Coating for Improved Reliability and Throughput in WLCSP

摘要

As more manufacturers look to increase the size of Wafer Level Chip Scale Package (WLCSP) dies andalso look to decrease the ball pitch, the susceptibility of the die to fail during thermal cycling and dropshock testing increases. The stress conditions introduced during thermal cycling from the mismatches inCoefficients of Thermal Expansion (CTE) lead to solder fatigue. The failure of WLCSPs during dropshock is found at the solder/pad interface. The general solution to address solder fatigue during thermalcycling and solder joint stress at the copper pad interface has been capillary underfilling the chips after chipattachment.To address these issues, a new material from LORD Corporation – SolderBrace? wafer applied coating,can be used to partially underfill the WLCSP die at the wafer level. This type of technology can be appliedusing existing equipment and processing techniques making these materials a more cost effective solution.This new material technology has enabled thermal cycling reliability improvements by replacing the finalpassivation layer with a new low CTE material as the partial underfill.This wafer applied partial underfill material technology has been successfully used to provide increasedthermal cycling and drop shock reliability in WLCSPs using a number of different methods that have beenpreviously described. The method to be discussed in this paper is a production process using a screenprinted, photo defined polymer system that does not require any in-process post cure.