Accurate Temperature Monitoring in Laser-Assisted Polymer Bonding for MEMS Packaging Using an Embedded Microsensor Array

This paper presents an experimental study of an accurate temperature-monitoring method using an embedded thin-film microsensor array for laser-assisted polymer bonding for MEMS packaging. The work is carried out using a fiber-coupled diode laser system and benzocyclobutene polymer as the bonding material. Beam-forming optical elements are used to generate top-hat and frame-shaped beam profiles. Platinum-based sensor arrays are fabricated using sputtering and ion-beam etching methods. Peripheral sensors are embedded at the interface between the polymer sealing ring on the top (capping) substrate and the sensor substrate in the bonding process. The embedded peripheral sensors allow precise monitoring of the temperature profile of the polymer track in the laser-assisted thermal curing process for substrate bonding. The sensor at the center of the array can monitor the temperature that would be experienced by a MEMS device in a manufacturing environment. Results show that accurate temperature monitoring can be obtained using the embedded sensor array. A lower temperature than that required for bonding is seen at the center of the bottom (device) substrate. This is a highly desirable effect for packaging of temperature-sensitive devices. In addition, the effects of substrate material and arrangement of heat dissipation on the resultant temperature profiles have been investigated.