Experimental Study On Fiber Self Alignment By Laser Soldering

Laser soldering system was used to study the passive self alignment of the fiber by using surface tension of the molten solder. Four parameters were ascertained to evaluate the self alignment effects of the fiber, including the stand-off height (SOH) of the solder joint, the pitch angle (β), the lateral excursion (D) and the yaw (γ); The three Demisional(3-D) geometry of solder joints were observed by laser scanning confocal Microscope (LSCM) and the 3-D coordinates of solder joints and fibers were measured. Furthermore, the factors that affects the alignment of the fiber were studied by comparison tests, including the laser soldering processing parameters, solder volume, shape and size of the pad.The effects of the laser soldering parameters on the alignment were studied. The experimental results showed that increasing the laser output power and heating time in a certain range could improve the wettability of the AuSn solder and the symmetry of the solder joint and promote the alignment of the fiber. However, the laser output power and heating time shouldn't be too high to make sure that the shape of the solder joint was well.Five solder volumes were applied for comparison, which were 0.011mm~3, 0.019mm~3, 0.025mm~3, 0.031mm~3 and 0.047mm~3. The experimental results showed that when the solder volume was 0.011mm~3, the solder didn't wet the whole pad and the solder joint was anisomerous, which worsened the alignment; when the solder volume was 0.047mm~3, the fiber was encircled fully by the solder, the capability of the alignment of the fiber was degraded greatly, since when the solder encircled the fiber fully, the imbalance of solder-fiber-air triple line was very small and the corresponding restoring force and torque was rather small. When the solder was enough to wet the whole pad and the fiber was encircled partially, the self alignment was better, in this case, with the solder volume increasing, the stand-off height of the solder joint, the pitch angle and the yaw all increased, and the lateral excursion decreased. The effects of the shape of the pad were studied. The results showed that when the laser soldering parameters and solder volume were fixed, for ellipse pads, with the length width ratio increasing, the stand-off height of the solder joint, the pitch angle, the lateral excursion and the yaw all decreased; for rhombic pads, with the internal angle increasing, the stand-off height of the solder joint, the pitch angle, the lateral excursion and the yaw all increased.The effects of the size of the pad were studied. The results showed that with the size of the pad increasing, the stand-off height of the solder joint decreased greatly, the pitch angle decreased little, the lateral excursion and the yaw increased greatly.Based on the experiment results, the regression models were presented for the stand-off height of the solder joint, the pitch angle, the lateral excursion and the yaw vs. the solder volume and the length width ratio of the ellipse pad.