Process Characterization and Reliability Modeling of Rigid-Flex Printed Circuits (RFPCs)

The trend in electronic packaging systems is driven by the increasing demand for miniaturization, functional densification and integration, and high reliability. To fulfil these higher requirements for electronic products and achieve higher reliability, great attention has been paid to Rigid-Flex Printed Circuits (RFPCs). The objective of this thesis is to characterize the key fabrication processes and to develop reliability models so that a reliable robust RFPC can be fabricated and its useful life extended.;The plasma etching process and lamination process are critical key processes that need to be characterized and optimized in RFPC manufacturing. In plasma etching process study, DOE was employed and the optimum set of etching process parameters was determined to simultaneously increase the etching rate while maximizing its uniformity. In lamination process characterization, DSC analysis and theological investigation were conducted to characterize the thermal performance the resin, and moreover the DOE study reveals the factors that have significant effects on the resin flow in RFPC lamination.;PTH reliability of RFPC was then comprehensively examined. The effect of materials and build-ups on PTH reliability of RFPC was firstly investigated through experimental approach. The thermal cycling results and the Weibull plots suggested the most suitable materials and build-ups to achieve better reliability. Finite element models (FEM) were then developed to simulate the stress and strain distribution along the PTH of RFPC and fatigue life was also predicted. A parametric analysis using the Taguchi method further found the influence of the critical factors on PTH reliability in RFPCs. Thirdly, an integrated analytical model that combines both the barrel deformation and the copper pad deflection together was developed to formulate the thermo-mechanical stress and strain in PTH. A good correlation was observed when comparing the parametric Taguchi analysis between the analytical model, finite element model and thermal cyclic experiment results.