Alpha Emission Rate Characterization and Risk Evaluation of Substrate Materials Used in Memory Packages

As the memory components are developed with continuously package downsizing, their soft error rates become more susceptible to the alpha particles induced from packaging materials. For the purpose to meet reliable performance of advanced memory products, packaging material suppliers are demanded to develop the materials to lower alpha emission rate (AER). The AER of the materials such as underfill, solder bump and pre-solder had been investigated in flip chip components with active side downward. However, the AER of the substrate materials like solder resist and core are rarely discussed and could be potentially resources of alpha particles, which may increase the soft error rate as the bump height and die gap are shrunk. In this paper, the AER of substrate materials are measured with different layered structures by using alpha particle counting system. Two types of cores (ultra-low and normal CTE ranges) performed different AER, which may be induced by different impurities in compositions. The effects of Cu foil coverage rate and thickness on substrate AER are also studied. Furthermore, the Monte Carlo simulation code is applied to calculate the emissive paths from substrate materials by considering energies detected from AER spectrum, isotopes decay series, and to further determine the risk of alpha particles in flip chip package.