Reliability Analysis of Solder Joints on Rigid-Flexible Printed Circuit Board for MEMS Pressure Sensors Under Combined Temperature Cycle and Vibration Loads With Continuously Monitored Electrical Signals

Abstract

The reliability of lead-free solder joints on flexible PCB has created significant new challenges in the industry, especially in automotive electronics, and possibly for future wearable electronics.In this paper, the submodeling technique was used to construct the finite element model of the rigid-flexible printed circuit board (rigid-flexible PCB) for a MEMS pressure sensor subjected to combined temperature cycle and random vibration loadings. During all the experiments, the electrical signals of each specimen were continuously monitored using an event detector. One advantage of this method is that any individual soldering interconnect failure will result in the diagnostic signal of the circuit, which could be detected in real time. The influence of vibration frequency and acceleration on the vibration fatigue life of solid joints was investigated.The research results are helpful to effectively characterize the performance of the MEMS sensors under combine thermal cycling test and vibration test. Two kinds of land shapes and two kinds of PCB assemblies were selected. The solder joint is sliced and the crack on the cross section of solder joint was observed. Results of finite element modeling analysis were consistent with the experimental results. Two design parameters have been identified in our research as being important to soldering usage in automotive environments: pad type (teardrop vs. non-teardrop) and pad size (big vs. small, matching size for Cu-wire and pad). Experimental results also showed that the solder joint with big land shape presented a relatively good thermal fatigue resistance.

Reliability of MEMS inertial devices in mechanical and thermal environments: A review

“…At high temperatures, thermal stresses generated by different materials can cause deformation of the sensor package, which can lead to bias and scale factor instability. The failure modes mainly include fatigue, fracture, open circuit, and delamination [ 62 , 63 ].…”