Design of Solder Joint for Self-Alignment in Optical Fiber Attachment Soldering

The self-alignment motion of optical fiber is critical to the low-cost and high-precision direct-coupling technology in optoelectronic packaging. In this research, the self-alignment method by using surface tension of molten solder and by adopting specific pad shape was proposed. First, the self-alignment model of solder joint in fiber attachment soldering was developed by using the public domain software called Surface Evolver and the three-dimensional (3D) geometry of solder joint with different pad shape was analyzed. Then, the self-alignment behavior of solder joint with an initial yaw misalignment was discussed and the theoretical equilibrium positions of five different pad shapes were calculated. Next, experiments were done to examine the theoretical equilibrium positions of these pads. The numerical results show that the theoretical equilibrium positions of ellipse pad are the major axis of ellipse, and it is much more appropriate for self-alignment. And the diamond pad and the combined pad have also self-alignment effects, but the square and the crisscross pad are not appropriate for self-alignment due to more than two equilibrium positions. The experimental results show the solder joint with initial yaw angle can be self-aligned to the theoretical equilibrium position of these five pads and solder joint of ellipse pad demonstrates smaller alignment error than that of diamond and combined pads.