The packaging technology of semiconductor is advanced and sophisticated for highly integration. The MCM and SiP is a modern technology used in IC packaging. There are passive tens components, multi chips and more than a hundred wires on the substrate. It is usual that Low yield happened in assembling process often when introducing a new product or process and it is difficult to find root cause in the sophisticate and highly integrated MCM IC. In this project, low yield problem for a new MCM IC assembling process was analyzed and solved using TRIZ systematic procedures. The Function Analysis (FA) diagram describes the relationship of the components and devices in the MCM package. In the FA, we use FA for device to analysis the total system of MCM and FA for process to analysis the MCM assembling process. We used CECA to figure out the negative factors including target factors and key factors. The CECCA were used to locate contradictions getting clear problem root cause of the MCM assembling system. Finally we use FA-solution directive to solve process and improve the yield. At the end, the yield problem was resolved from almost 0% to 99% saving a couple million NT Dollars for the new product introduction. This project presents a systematic procedure to solve the complex system. Key words: MCM, SiP, substrate, yield, TRIZ, FA, CECA, CECCA.