Wetting Behavior Of Sn-9Zn Solder On Intermetallic Compounds Layer

The development of lead-free in electronic packaging field brings many new problems, and one of them is how to improve the poor wettability of lead-free solders. This study is focus on the wetting behavior and the growth behavior of interfacial intermetallic compounds for Sn-9Zn solder alloy on Cu substrate and Cu4Zn8/Cu substrate to find a new method to improve the poor wettability of Sn-9Zn lead-free solder. The wettability of Sn-9Zn solder on Cu4Zn8/Cu substrate and Cu substrate, and the shearing strength of Cu/Cu5Zn8/Sn-9Zn/Cu5Zn8/Cu and Cu/Sn-9Zn/Cu soldering joints at different reflowing parameters have been researched to prove that the use of Cu5Zn8/Cu substrate in improving the wettability of Sn-9Zn solder is feasible, and the best reflowing parameter range have been obtained in the meantime. The conclusions were summarized as follows:(1) The prepared Cu5Zn8intermetallic compounds layer on Cu substrate can improve the poor wettability of Sn-9Zn solder alloys effectively. The wettability of Sn-9Zn solder ball increase with increasing reflowing time on Cu5Zn8substrate, while the wettability increase with increasing reflowing time at first, and decrease slightly as the time going on Cu substrate. The wettability on Cu5Zn8substrate is better than Cu substrate at the whole rang of reflowing parameters.(2) The average thickness of interfacial IMC layer of Sn-9Zn/Cu5Zn8/Cu and Sn-9Zn/Cu increase with increasing reflowing time and reflowing temperature. The growth level of interfacial IMC of Sn-9Zn/Cu5Zn8/Cu is less than Sn-9Zn/Cu as the reflowing time and reflowing temperature increasing.(3) There is a relationship between the morphology and average thickness of interfacial IMC layer and the wettability. The wetting reaction on Cu5Zn8/Cu can be regard as inert wetting, and the roughness value Rrms/λa of the IMC layer for Sn-9Zn/Cu5Zn8/Cu interface changes from0.316to0.998, while the roughness value Rrms/λ a of the IMC layer for Sn-9Zn/Cu interface changes from0.257to0.603, The roughness higher, the better wettability of Sn-9Zn solder.(4) The shearing strength of both Cu/Cu5Zn8/Sn-9Zn/Cu5Zn8/Cu soldering joints and Cu/Sn-9Zn/Cu soldering joints increase with increasing reflowing temperature at first and then decrease. The shearing strength of Cu/Cu5Zng/Sn-9Zn/Cu5Zn8/Cu soldering joint is less than that of Cu/Sn-9Zn/Cu soldering joint at a lower reflowing temperature; while the Cu/Cu5Zn8/Sn-9Zn/CusZng/Cu soldering joint’s shearing strength is higher at a higher reflowing temperature. The shearing strength of Cu/CusZng/Sn-9Zn/CusZns/Cu soldering joints increase with the increasing reflowing time all the time. While The shearing strength of Cu/Sn-9Zn/Cu soldering joints increase with the increasing reflowing time at first, and then decrease as the time going. The two kinds of soldering joints have a equal shearing strength when the reflowing time is change from120s to300s.(5) Considering of the wettability and average thickness of interfacial IMC layer of Sn-9Zn solder alloy on ordinary Cu substrate and CusZn8/Cu substrate at different reflowing parameters, and the shearing strength of Cu/CusZns/Sn-9Zn/CusZn8/Cu and Cu/Sn-9Zn/Cu soldering joints, we can conclude that the CusZns/Cu substrate has an advantage on application at a longer reflowing time (120s-300s) and a higher reflowing temperature (260℃-270℃).