Copper pillar WLCSP device embedded in large PCB module with passive devices to create one hybrid package are growing widely in smart communication and mobile electronic devices. The crucial challenges in electrical testing and failure analysis on it are to remove the embedded copper pillar CSP device from the module without inducing mechanical defects, and solder ball placement on the CSP for ATE testing. This paper discusses the sample preparation process step-by-step, which includes de-soldering of external components from the PCB, top side up and down parallel polishing to remove copper pillars, chemical etching the PCB module, solder ball placement on CSP devices and the soldering process on a plain coupon board. The established process enables electrical testing, evaluations and failure analysis performed on a demounted CSP device. A simulation of an electrical testing and failure analysis will also be highlighted in this paper.