Effect of Manufacturing Stresses to Die Attach Film Performance In Quad Flatpack No-Lead Stacked Die Packages

Problem statement: Repeated heat cure during assembly processes affected the Die Attach Film (DAF) material properties and the effectiveness touched area that leads to weak die bonding and delamination. Suitable die attached condition and DAF material selection had been evaluated to achieve required reliability performance in the manufacturing of the 3D Quad Flat No-Lead (QFN) stacked die package. Approach: During this study, special attention was given to the development of the residual stresses due to mismatch in the coefficients of thermal expansion of different DAF materials. Both experimental and finite element method were employed to gain a better understanding in a stress development induced between two different type of DAF, different die attach temperature and during the manufacturing process. Differential scanning calorimetry (DSC) was used to measure the changes of heat flow characteristics for both types of DAF. The die bond strength results measured using shear testing machine were compared with the finite element method prediction. Results: Although both DAF samples achieved good reliability performance and passed the Moisture Sensitivity Level 3 test (MSL3) at reflow 260°C without any sign of delamination, numerical simulation had demonstrated that the stress development were increased exponentially as the die attach temperature increased. It showed that different DAF gave different values of stresses but presented the same trend which the lowest die attached temperature (100°C in comparison with 125°C and 150°C) gave more stress to the die and possibility that the die will have weak adhesion to the substrate was high. Conclusions/Recommendations: Therefore for this case, stress can be relieved by having higher die attached temperature with an adequate bonding force and time, however die attached temperature for both DAF must be used above the glass transition temperature (128°C for DAF A and 165°C for DAF B) and being controlled not to exceed the crystallization temperature (203°C for DAF A and 204°C for DAF B) of both DAF.