Abstract
Eddy current is a promising induction heating and actuation approach for MEMS processes and devices. This study has discussed the scale effect of eddy current for mirco electroplating microstructures through the analytical and experimental means. The results show that the induction heating rising temperature varies with the in-plane surface area of microstructure and the relative permeability of thin-film materials. Moreover, the shape of microstructure also leads to the different of rising temperature. Thus, localized heating is achieved on substrate by applying an external high frequency magnetic field. It is also easy to tune the heating temperature by varying the area of magnetic film; in other words, the photolithography can define various temperature regions on substrate. Three applications are presented in this study: (1) Localized heating for wafer level packaging. The electroplated thick film acts as a heater and a spacer. It takes only several seconds to complete the solder reflow and bonding process, and hermetic seal of the packaged device is achieved. The bonding strength is up to 18 MPa. The integration the MUMPs devices with this packaging technique have been demonstrated; (2) Localized positioning and welding for 3D microstructures. The lifting and welding can be localized by the magnetic film. Moreover, a global wafer level process can be achieved by the magnetic field; (3) Coil-less Lorentz force for optical scanner. The eddy current is induced in ferromagnetic material by solenoid, thus, the complicated coil routing and insulation layer deposition for current is prevented. This study demonstrated a 2D scanning mirror with 20 mechanical scan angles when operated at 100mV and 0.016mA.