Temperature monitoring in laser assisted polymer bonding for MEMS packaging using a thin film sensor array

Laser assisted polymer bonding is a novel technique for MEMS packaging, which can offer a short bonding time and reduce the thermally induced stress during the packaging process. However, due to the localised nature of the temperature rise, it is difficult to monitor the temperature change precisely during the bonding process using the conventional methods. In this paper, the development of thin film miniature temperature sensor arrays is presented for in-situ temperature monitoring in the laser assisted polymer bonding process. A high-power fibre-coupled diode laser at the wavelength of 970 nm was used as the heat source for benzocyclobutene (BCB) bonding/curing in conjunction with novel beam forming optics that allows selective illumination of the substrates to be joined. Instead of using infrared detectors and temperature-sensitive paints in our previous work, thin film microsensor arrays were designed and fabricated on both glass and silicon substrates for obtaining the precise in-situ temperature change and the thermal distribution during the laser bonding process. The minimum track width of a meander sensor in the array was 3 mum resulting in a foot print of only 250 mum times 240 mum for the smallest sensor. The key parameters of the laser bonding process, such as laser beam profile, power and the resultant thermal responses, were investigated as well as the effect of the thermal arrangement underneath the substrate assembly.