Mechanical characterization of RCC and FR4 laminated PCBs and assessment of their board level reliability

Abstract

The role of electronic packaging is becoming more important and now constitute a much bigger percentage of the development of package with high evolution due to strong and competing demands for increased functionality and performance, further miniaturization, heightened reliability, and lower costs. Various types of packages like BGA and Quad Flat No-Lead (QFN) are widely used. Ball Grid Array package was developed out of the need to have a more robust and convenient package for integrated circuits with large numbers of interconnects. Moreover, BGA uses efficient board space, improved thermal and electrical performance, reduced package thickness and improved reworkability resulting from larger pad size. The different layers with different material properties inside the PCB (Printed Circuit board) make the PCB highly orthotopic. Additionally, prepreg materials are viscoelastic and they provide some sort of stress relaxation and creep characteristics. Currently, there are two types of boards that are used with BGA packages. One of the types has RCC film as the uppermost and lowermost prepreg substrate while the second type has FR4 film as the uppermost and lowermost prepreg substrate. By using Dynamic Mechanical Analyzer (DMA), time and temperature-dependent viscoelastic properties of the board are obtained. Using Thermomechanical Analyzer (TMA), Coefficient of Thermal Expansion (CTEs) of the boards are obtained. In summary, in this study, the mechanical characterization of BGA PCBs with FR4 and RCC is presented along with the thermal cycling simulation results from ANSYS and the reliability of two types of boards were compared. The computational analysis includes lumped and layered model for detail analysis. The Volume averaging technique is implemented to calculate the strain energy density. The Critical solder joint is determined from the static structural analysis under thermal loading.