Plastic Ball Grid Array Reflow Using a Fast-Modulated CW Laser

Abstract
Plastic ball grid array reflow using a fast-modulated CW laser is studied. A CW/Q-switched Nd:YAG laser is modified to work in the fast-modulated CW mode. Sn–Pb eutectic solder balls with a diameter of 760 µm and Au–Ni–Cu solder pads are used in the study. By varying the laser power and the laser-on time, respectively, the solderable parameter region of laser reflow for the solder balls and the solder pads is obtained. Shear strength tests are also performed to find out the optimal reflow parameters. The measured shear strength is higher than 1500 gf, with the maximum value over 1900 gf. An energy equilibrium model is proposed to compare the solderable region predicted theoretically with the experimental results and to estimate the average temperatures of solder joint under the given experimental conditions.