Controlling the solidification speed toward enhanced failure energy of Sn-0.7Cu system solder ball-attaches with alloy design using instantaneous large-area laser soldering

초록

The combination of the instantaneous large-area laser soldering process with Sn-0.7Cu-0.2Cr solder materials showed exceptional microstructure changes and mechanical behaviors compared to conventional solder and process. The conventional joint strength was 41.81 MPa, while the new joint strength was 52.11 MPa, representing an increase of about 25 %. Although the immiscibility of Cr and Sn was a fundamental limitation, the rapid cooling rate with minor Cr elements caused the enhancement of kernel average misorientation (KAM) between Sn and Cr, leading to the increment of bonding strength. The parameters of the solder composition and processing method did not follow the Hall-Petch relationship, which can be explained by the strengthening of other mechanisms. The rapid solidification of the laser soldering and the addition of Cr elements induced the lattice distortion inside the solder, which was positively contributing to increase the mechanical properties. Dominant enhanced mechanism and behavior was clarified through combined analysis with simulation of solidification behavior, electron backscattered diffraction (EBSD) and X-ray diffraction (XRD).

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