Abstract
Due to the current trend of semiconductors toward higher frequency and better performance, both the structural reliability and the electrical performance of electronic packages can significantly affect the packaging system performance. Therefore, for the electronic packaging design, the mechanical behavior and the electrical performance should be taken into account simultaneously when designing IC chips that operate in the microwave frequency range. Based on the above, this investigation proposes methodologies to analyze and design the electronic packages regarding the mechanical as well as the electrical performance aspects, and to study and integrate the correlation between the reliability and microwave effects in the design methodology development of advanced electronic packaging applications. A flip chip package, showing good electrical performance and high reliability is selected for this research. To study the aforementioned concerns, the design parameters that can influence the mechanical and electrical performance of a flip chip package are extensively investigated through finite element method (FEM) and several experiments. Through FEM simulation, the mechanical and electromagnetic behavior of the electronic packages could be comprehended and allowing for the parametric as well as factorial analyses of the packaging performance. Moreover, to investigate the solder joint reliability (applying accelerated thermal cycle testing (ATCT)), the IMC growth effect (applying high temperature storage experiment) and the microwave frequency response (applying vector network analyzer (VNA) microwave signal measurement), the following test vehicles: (1) no-underfill flip chip with different solder bump structure, (2) lead-free (96.5Sn/3.5Ag) and eutectic (63Sn/37Pb) solder flip chip with different solder bump structure, (3) lead-free and eutectic solder on Ti/Cu/Ni under bump metallurgy (UBM) layer fabricated upon a copper chip and (4) microwave signal transmission utilizing flip chip are designed, fabricated and tested. The experimental results for the IMC growth effect on the solder bump strength indicate that after isothermal aging treatment at 150oC for more than a 1,000 hours, the Sn/Ag solder reveals a better maintenance of bump strength than the Sn/Pb solder, and the Sn/Pb solder shows a higher IMC growth rate than the Sn/Ag solder. In terms of flip chip package reliability testing, the ATCT experimental results show that the underfilling, die/substrate-side pad size and solder bump volume do indeed play a significant role in the solder joint reliability. In addition, the flip chip utilizing Sn/Ag solder shows a slightly better solder joint reliability than that utilizing the Sn/Pb solder. For VNA microwave signal measurement, the designed microwave flip chip is proven to be feasible under the operation frequency of 3.2 GHz. In addition, to demonstrate the FEM analysis methodologies, the FEM simulation results are compared with the experimental data. The findings indicate that the FEM simulations have good agreement with the experimental results in both mechanical reliability and microwave electrical performance. This confirms the feasibility of the design/analysis methodology developed in this study. Furthermore, based on the validated FEM analysis, the FEM factorial design for the design parameters of the solder joint geometry, substrate thickness and underfill filleting type are employed to study the influence of the design factor sensitivity and the interaction among factors on the flip chip packaging reliability. In order to investigate the correlation of the mechanical and electrical performance of the electronic package, the IMC layer growth and the underfill fillet type experiment are employed. As is known, the IMC layer formation apparently influences the solder bump mechanical strength, as is contrary to the mechanical impact, the microwave signal testing result shows that there is no significant microwave signal variation that is affected by IMC growth. On the other hand, the microwave signals of test vehicles with a different underfill fillet (without underfill, with peripheral underfill and with full underfill) are measured, and in addition, the solder joint reliabilities of the test vehicles with different underfill fillet are analyzed as well. The findings show that the flip chip with peripheral underfill, showing a qualified microwave signal performance and an excellent mechanical reliability, is recommended for the practical application. Based on the above, the development of design/research methodologies of the mechanical reliability and the microwave signal performance of electronic packages, and moreover, the integrated discussions between the design considerations of mechanical and electrical aspects of electronic packages which are often investigated independently are the major contributions of this research.