Flip-chip And Related Issues

With the rapid development of microelectronic industries, the reduction of feature size, growth in wafer size will continue in semiconductor industry. There is a crucial need for IC packaging to move to higher density, higher performance and lower cost. Flip Chip technology, by offering almost ideal density and superior performance, and could become the mainstream technology in the future. There are numerous investigations overseas, focused on the structure, materials, processes and reliability, etc. However in China, few systematic investigations were reported. In this project, flip chip on board (FCOB) technology was studied both experimentally and theoretically. The effort aim is promoting research activities in the field. Also it is considered to be important for the coming mass production with flip chip technology in the future. Undestructive inspection is an important technique in the reliability study on the microelectronic packaging. The undestructive inspection of high frequency (230MHz) scanning acoustic microscopy (SAM) is applied in our experimental study. It can be seen that not only the SAM is highly sensitive on the underfill delamination, but also the fatigue crack initiation and growth is directly coincide to the contrast variation of solder joint in C-SAM images during reliability test. Therefore the degree of solder joint fatigue of FCOB can be qualitative detected through comparing the contrast variation of the C-SAM images without destruct the sample. So the rather precision information in reliability investigation on FCOB can be accumulated through SAM inspection. The thermal fatigue lifetime of SnPb solder joints can be greatly increased by applying underfihl encapsulant in FCOB. However, the underfill delamination could correspondingly effect the reliability of solder joints. By conducting thermal cycling test and two-dimensional finite element simulation on the FCOB with different underfihl materials, the relationship between the underfihl delamination and the SnPb solder joint reliability is investigated. The results show that the underfihl delamination initiates at the edge of chip/underfill interface. If an underfihl did not have a good adherence to the chip, the fatigue crack initiation and propagation in the solder joints is caused directly by the incipient underfihl delamination. On the other hand, if an underftll had a good adherence to the chip, the dominant failure mode should be the fatigue crack in the solder joints. It is shown that the mechanical coupling effect of the underfihl could be weakened by the underfihl delamination, which should influence lifetimes of the solder joints. The processes are optimized to decrease the occurring of underfihl delamination. By conducting thermal cycling test and three-dimensional global finite element simulation, the thermal fatigue failure of SnPb solder joints of different size FCOB is investigated. The results show that plastic strain range in the solder joints is decreased to nearly an order of magnitude after underfihling, therefore degrades thermal fatigue failure of the solder joints subsequently. Since the thermal stresses and strains in the solder joints are redistributed due to the application of underfihl, the locations of thermal fatigue crack initiation and propagation in the solder joints are changed. Furthermore the height of the solder joint is found irrelevant to the thermal fatigue life of SnPb joints in Flip Chip. Heterogeneous coarsening is observed on both Sn-rich and Pb-rich phases after...