Reliability study and technology development of solder-bumped flip chip on low-cost substrate

The fine-pitch electroplating-based solder bump fabrication process has been developed. The effect of the UBM and electroplating process of solder bump on the shear strength of solder bump was studied as well as the relationship between the shear test failure mode and solder bump fabrication process. The aging testing and the temperature-humidity testing with various test time were performed for the samples. In the study, four types of low-cost PCB designs of the fine-pitch solder-bumped flip-chip were evaluated. Various size test chips were used in the experiments. The concept of wetting area error ratio was introduced to quantify the change of the designed wetting area on PCB and the actual wetting area. The chip size and the solder bump parameters determined the alignment tolerance required on the PCB. The geometry-based model was used to model the solder joint shape and predicted the failure mechanism of solder joint during the bonding process. The formation and the effect of voids in the underfill material were analyzed and studied.; Flip-chip-on-flex (FCOF) technology has been developed for various size chips and various flexible substrate designs. The warpage of flexible substrate was critical to the bonding process and the underfill process. The reliability of solder joints in FCOF was evaluated and tested using thermal cycling and temperature/humidity tests. The adhesion of solder mask, Cu trace and substrate determined the shear strength of flip chip assembly. Most of shear failure located at the interface between the solder mask and the flexible substrate. A pressure sensor and an actuator were also assembled on a flexible substrate using FCOF technology. A photolithography process was developed to meet the solder bump fabrication requirement of the sensor chip. The flexible substrate and flip-chip process were designed for the MEMS package. The electrical test results of the MEMS package satisfied the requirements of devices.