In situ study the effects of Cu addition on the rapidly growth of Cu6Sn5 at the Sn-base solder/Cu L-S interface during soldering heat preservation stage

Synchrotron radiation x-ray real-time imaging technology was used to study the interface reactions of Sn/Cu and Sn0.7Cu/Cu joints during reflow with soldering time of 1h under temperature of 300/350 degrees C. This experiment allows us in-situ observe the interfacial IMCs growth and completely avoids Cu6Sn5 precipitation from the solder in cooling stage to affect the morphology and thickness of interfacial IMCs. This work is a foundation work to establish quantitatively sufficient as well as accurate data for IMC growth under isothermal reflow soldering on one hand and be viewed as the non-destructively evaluated results on the other hand. It is in-situ observed that the IMC morphology is scalloped during the heat preservation stage at both two solders/Cu interfaces. Comparing with pure Sn solders, the Sn0.7Cu solders are observed with interfacial IMC of greater thickness, greater number of grains, smaller base width and more substrate consumption. During the heat preservation stage, all of the growth kinetic index (n) is close to 1/3 indicating that grain boundary diffusion determines the interfacial reaction. The mechanism of Cu addition to affect interfacial reaction by changing the microstructure of solder matrix is clarified, and then the morphology and thickness of interfacial IMCs can be controlled by alloy elements addition to improve the soldering reliability of electronic packaging.