Selective removal by laser processing for the sensor mold

In order to achieve the stress free structure of the sensor chip, it is necessary to remove the epoxy molding compound (EMC) around the sensor chip. However, removing the EMC close to the sensor chip may damage the sensor chip, and it adversely affects the sensor characteristics. Therefore, it is necessary to develop the processing method that can remove only EMC without damaging the sensor chip. As the processing method, Er:YAG laser is adopted by focusing on the difference of energy absorption rate vs. wavelength between the sensor chip and the EMC. In order to measure the difference of energy absorption rate vs. the laser wavelength, FT-IR was selected Moreover, a laser energy distribution was visualized by a laser beam analysis of a spherical aberration characteristic, and the damaged zone of the sensor chip and the removed zone of the EMC within the laser spot diameter were clarified. With 2940nm wavelength Er:YAG, energy absorption rate of the sensor chip is 12.7% and that of the EMC is 95.5%. From this result, it is estimated that the resin close to the sensor chip can be removed due to high energy absorption rate and the sensor chip is not damaged due to low energy absorption rate. In addition, by visualizing the energy distribution of the laser, the focus position is considered to achieve both the selective removal and a processing time. As a result, selective removal can be achieved by setting the focus position to 0.4 mm out of focus side.