We present a diagnosis methodology for assembly failures in RF front-end circuits embedded in System-in-Package (SiP) designs. We focus on technologies where nonlinear components reside on several active dies and the linear components reside on a passive base. While there can be many pin connections between the base and the active die in these designs, there are only a few outside pins available. We present a systematic analysis technique to select viable test conditions to distinguish among the faults. Normal operation mode as well as non-functional mode test signals are used to increase the diagnostic resolution. We show that most assembly faults can be distinguished from one another using non-functional mode test signals on a generic LNA circuit. We also apply our technique to a commercial tuner for a subset of representative faults and reach the same conclusions.