A pressure sensor using flip-chip on low-cost flexible substrate

The packaging of microelectromechanical systems (MEMS) is complex and it is essential to the successful commercialization of many MEMS devices. In this paper, a pressure sensor and an actuator were assembled on a flexible substrate using FCOF technology. A photolithography process was developed to meet the solder bump fabrication requirement of the sensor chip. Eutectic solder bumps (63Sn/37Pb) with 250μm pitch were fabricated using the electroplating process. 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. The samples were evaluated and inspected using various techniques, such as scanning acoustic microscope (SAM), X-ray imaging, scanning electron microscopy (SEM), etc. The flatness of the flexible substrate was essential to the underfill process and reliability of FCOF technology. Most of shear failure located at the interface between the solder mask and flexible substrate after the flip-chip assembly.