Decapsulation technique using electrochemical etching for failure analysis of WLCSP n-type Si assembled module devices

Module devices consist of many electronic components mounted on a glass epoxy resin substrate. In failure analysis of the module device, it is necessary to expose the electronic components while maintaining these full functions. We have developed an electrochemical etching technique to decapsulate the overcoated anhydride cured epoxy resin. The method utilizes KOH alkali solution with DC bias voltage applied to a wafer level chip size package (WLCSP) n-type Si device. The DC bias acts as an electrical-etch-stopper of the n-type Si device’s substrate during the decapsulation of the overcoated resin. The efficiency and effectiveness of our decapsulation technique were evaluated using a Li ion/polymer protector module device. The mechanism of the electrochemical etching is also discussed.