Impact of substrate materials on packages warpage

Unit warpage in Ball Grid Array (BGA) packages with different substrates due to coefficient of thermal expansion (CTE) and Young's Modulus mismatch was investigated. The effect of substrate materials on BGA packages warpage was analyzed. Thermal Mechanical Analyzer (TMA) and Dynamic Mechanical Analyzer (DMA) were used to measure Glass Transition Temperature (Tg) and CTE and Young's Modulus of the substrates and the properties of these substrates were analyzed. Shadow Moiré was used to measure the unit warpage at room temperature (25°C) and during reflow. A Finite Element Analysis (FEA) method was used to simulate the warpage results to compare with results from the experiment and to verify the results. From this work, Cu, core materials, and solder mask (SM) have a combined effect on Tg, CTE and Young's Modulus of the substrate. Higher CTE of substrate than that of moldcap results in units presenting Cry, and compared with CTE, the modulus plays a dominate role in the strip compress and decreasing modulus of substrate helps to lower unit warpage. The Shadow moiré test results and the simulation results state that the two results are credible.