Impact of advanced materials on power cycling performance and process dependent stresses of QFN

Due to different demands, there are many types of die attach technologies in the market. In this work, die attach materials such as solder, silver filled epoxies and sintered silver are investigated for their mechanical performance under standard processing steps and under power cycling conditions for a quad-flat no-leads package (QFN). In addition, two molding compounds, one with thrice the thermal conductivity of the reference molding compound are analyzed. A combination of experimental and finite element analysis suggested that, sintered silver die attach material is the most susceptible to failure at the die attach layer while one of the epoxy filled die attach material investigated is the least susceptible to failure in a QFN. However, sintered silver seems to induce the least die stress at peak solder reflow temperature. Although sintered silver had superior thermal conductivity, the temperature within the package during power cycling is very similar to the other die attach candidates. It appears that higher thermal conductivity of the die attach material and molding compound do not lead to an increase in fatigue life of the solder joining the package onto the board.