Defect Z-depth Determination in Flip-chip using lock-in thermography

This paper describes the use of Lock-In Thermography (LIT) technique to determine the defect Z-depth in flip chip. An empirical phase shift versus applied lock-in frequency plot for Flip-chip is first created by using samples with known defect Z-depth. The actual experimental phase shift data from reject samples with unknown defect locations are then measured and compared against the empirical phase shift plot. The defect Z-depth of these samples are determined by comparing where the experimental phase shift data points lies with respect to empirical phase shift plot and validated with Physical Failure Analysis (PFA).