Thermal Characters Analysis of Induction-Self-Heating-Reflow for Solders Bumping

Induction-self-heat-reflow technology (ISHR), which has the advantages of 3-D selective heating and high heating speed, can solve the problems which can´t be controlled in traditional reflow technologies, such as inhomogeneous heating of ball grid array (different bumps), simultaneous heating of chip and carrier with solder ball, etc., which have been increasingly serious with the development of packaging technology. The focus of this study was on discussing a new reflow method ISHR used for high-density area array packaging and assembly interconnections. Multi-layer under bump metallization (UBM) and Sn3.5Ag lead-free solder ball were laid in the high frequency electromagnetic field. Because of the induction heating, solder balls with low melting point melted and spread on the UBM to form the solder bumps and interconnections. The experiment results showed that the effective solder bumps could be formed within 2 s through this method. At the same time, the infrared temperature measurement results showed that the temperature was lower on the rosin substrate 0.5 mm far away from the edge of pad. The input thermal quantity to the rosin substrate by ISHR method was much smaller than that by those global heating processes. A thermal physical model was built to calculate the heating power. And the calculating joint temperature change curve matched the actual curve quite well