Growth behaviors of intermetallic compounds on the Sn-0.7Cu-10Bi-xCo/Co interface during multiple reflow

The Sn-0.7Cu-10Bi-xCo/Co (SCB-xCo/Co) interface reaction during soldering process, and the growth and evolution of intermetallic compounds (IMCs) after multiple reflow were investigated. The experimental results indicated that the IMCs layer was successively delaminated, dissolved and aggregated during multiple reflow, and the IMCs layer was thickened with increasing reflow cycles. The results further showed that the IMCs layers of SCB/Co and SCB-0.20Co/Co interfaces were 11.19 mu m and 26.27 mu m thick respectively after one reflow. The scallop-shape and flat-shape IMCs layers were generated on the SCB/Co and SCB-0.20Co/Co interfaces during initial reflow. The scallop-shape IMCs layer was transformed into the flat-shape one with increasing reflow cycles on the SCB/Co interface. Co in the solder played a role of purification, and it could decrease the concentration gradient of Co atom on the IMCs/solder interface to inhibit the Co-containing compounds growth. The IMCs were stratified due to reduction of Co concentration on the SCB/Co and SCB-0.20Co/Co interfaces after reflows, respectively. With the increase of reflow cycles, the decrease of Co concentration on the interface caused IMCs obviously to be dissolved into the liquid solder, and the free-state compounds particles were reassembled and grew up under the effect of the adsorption force. (C) 2019 The Author(s). Published by Elsevier Ltd.