A quantitative study of die crack in leaded IC package

Die crack in plastic package is a reliability failure. There are multiple factors influencing the die crack in plastic package, such as integrity of die, integrity of package, stress condition in board soldering, stress condition in field application and etc. The focus of this study is on the integrity of die. Finding the critical factors of a die crack is crucial in root cause investigation. A quantitative analysis method is essential. In this study, a new quantitative die crack analysis method is established based on 3 in 1 approach, "FEA-Fredric equation-fractography". 3D finite element analysis (FEA) was applied to estimate the package stress onto the die under known IR reflow condition. Fredric Ericson and Jan-Ake Schweitz\´s equation was used to estimate the ideal fracture strength of the sample dies with known flaw size. Fractography is applied for cracked die analysis to determine the actual critical flaw size. It assumed that die crack is expected if the stress on the die is greater than the die fracture strength. To validate the new method, soldering reflow experiment was carried out. The test vehicle selected is a TQFP128 package. Experimental matrix was designed to determine or verify the stress on the die and the response of the die with different backside roughness under various soldering peak temperature. A clear relationship between die crack and chip backside flaw size and peak reflow temperature is observed. Results showed that higher stress is induced on the die at a higher peak temperature. Results proved this new "FEA-Fredric equation-fractography" method is a sufficient and effective analysis method for root cause and failure mechanism investigation for die crack in plastic IC package