This paper presents a root cause analysis case study of defective Hall-effect sensor devices. The study identified a complex failure mode caused by chip-package interaction, which has a similar signature to discharging defects such as ESDFOS. However, the study revealed that the defect was induced by local mechanical force applied to IC structures due to the presence of large irregular-shaped filler particles within the mold compound. Extensive failure analysis work was conducted to identify the failure mode, including the development of a new backside analysis strategy to preserve the mold compound during IC defect localization and screening. A combination of different failure analysis techniques was used, including CMP delayering, PFIB trenching, SEM PVC imaging, and large area FIB cross-sectioning. The study found that the mold compound of the package caused thermos-mechanical strain onto the silica filler particle due to epoxy shrinkage during the molding process. Additionally, extra-large, irregularly shaped filler particles (called twin particles), located on top of the chip surface, can cause locally high compression stresses onto the IC layers, initiating cracks in the isolation layers under certain conditions forming a leakage path over the time. Thermo-mechanical finite element analysis was applied to verify the mechanical load condition for these large irregular-shaped filler particles. As a result, an additional polyimide layer was introduced onto the IC to mitigate the mechanical stress of mold compound particles to avoid this failure mode.

It has been shown that microscopic Lock-in-Thermography (LiT) can be used for localization of electrical active defects like shorts and resistive opens in integrated circuits. This paper deals with the application of LiT for non-destructive failure analysis of fully packaged single and multi chip devices. In this case inner hot spots generated by the electrical defects typically can not be imaged directly because the mold compound or adhesives above are not IR transparent. Inner hot spots can only be detected by measuring the corresponded temperature field at the device surface. By means of failed and test devices will be shown, that LiT is sensitive enough to measure such temperature fields. In addition to the lateral localization of inner hot spots its depth can also be determined by measuring the phase shift between the electrical excitation and the thermal response at the device surface. Furthermore, the influence of the lock-in-frequency and mold compound thickness to lateral resolution and signal to noise ratio will be discussed. Using real failed single chip and stacked die devices two analysis flows were demonstrated to locate inner defects.