Effect of Interaction Between Multiple Defects on Z-Depth Estimate in Lock-in Thermography Applications

In the recent years, 3D packaging has become a major enabler for heterogeneous integration of multiple functional devices and different nodes into a single package. The integration of multiple devices into 3D packages poses significant challenges when it comes to electrical fault isolation and failure analysis. With 3D packages, non-destructive fault isolation is important so as to accurately isolate the defect to the specific part of the failing package. This is critical since the different components in a 3D package are often owned by different suppliers and accurate non-destructive fault isolation will facilitate further root cause analysis and failure disposition by the concerned suppliers. Much higher sensitivity and better resolution in defect depth are two critical capabilities required for 3D packages. Lock-in Thermography (LIT) is a powerful non-destructive fault isolation technique for thermally active defects in semiconductor packages. With the integration of multiple components into 3D packages, the challenge lies in the added complexity in terms of the number of active devices and routing inside the package. More often than not, we have multiple defects inside the package at the same time. This study presents a fundamental analysis on the interaction between multiple defects in a package and its effect on defect depth estimate accuracy in lock-in thermography applications. In addition, data from real test cases have also been presented, which help better understand the interaction between multiple defects and provide confidence in the proposed correlations. The learnings from this study will facilitate tool and technique development and benefit failure analysis and 3D package development community.