Application of Lock-in-Thermography for 3d defect localisation in complex devices

This paper presents the application of lock-in-thermography (LIT) for localisation of electrical defects in fully packaged microelectronic and microsystem devices. It will be shown that inner electrical defects like shorts and resistive opens can be found in a nondestructive way by thermal imaging of the device surface. 3-dimensional localisation of inner defects can be enabled by measuring the phase shift between the electrical excitation and the thermal response at the surface using LIT. In addition, thermal simulations were used calculating phase shifts depending on mold compound thickness above an inner heat point source. The calculated data were compared to experimental results. Furthermore, the essential influence of the Lock-in-frequency for optimization of spatial resolution and sensitivity will be discussed.