Solder Reflow Method and Reflow Temperature Profile

ABSTRACT The major cause of integrated circuit package failure mechanisms such as delamination, internal cracking or popcorning is package saturation with moisture and subsequent exposure to high temperature during the solder reflow process. Different reflow methods and reflow temperature profiles have shown to be an important factor affecting this type of failure mechanism. A series of tests were carried out using three plastic packages as test vehicles. The studied packages are Plastic Ball Grid Array (PBGA), Thin Quad Flat Package (TQFP) and Plastic Quad Flat Package (PQFP). A large amount of testing has been done by Motorola on plastic packages in order to optimize the process condition, material compatibility and reliability. In our studies we have proven that the PC board solder reflow process can have a significant impact on the package reliability performance. To better understand the impact of different reflow methods and temperature profiles, an experiment was carried out to evaluate reflow methods and reflow temperature profiles. The evaluation and comparisons were done on 196 PBGA, 144 TQFP and 132 PQFP packages. The evaluated reflow methods were vapor phase reflow and convection reflow. Nine different reflow temperature profiles were studied in these two methods. The variations of the profiles were ramp rate, preheat time, dwell time and peak temperature. The study also included JEDEC standard vapor phase and convection reflow temperature profiles. The interfacial integrity of the packages were examined by using scanning acoustic microscopy with C-SAM and THRU-scan™ method, after JEDEC moisture preconditioning, followed by reflow. The packages were evaluated for delamination (popcorn) performance and compared for the influence of different reflow methods and different variables in reflow temperature profiles. The results show that the severity of plastic package cracking and delamination can be highly dependent on the solder reflow parameters. The dominate reflow factor is total heat energy applied to the package through out the period of reflow time. The higher the temperature and the longer the dwell time, the more likely a package is to crack, if the moisture level inside the package is nearly at, or above the critical level.