cooling rate and aging treatment on the formation and thickness of intermetallic compounds(IMC)in Sn-9Zn/Cu interface were investigated.For comparison
the interfaces of Sn-3.5Ag-0.7Cu/Cu and Sn-37Pb/Cu at the same condition were also examined.Two reaction layers are formed at the Sn-9Zn/Cu interface:Cu-Zn layer adjacent to Cu substrate
and Cu-ZnSn compound layer adjacent to the solder.In addition
O element is also detected at the interface between the Cu-Zn layer and Cu-Zn-Sn layer.The results also show that melt superheating degree and cooling rate have great effect on the thickness of the reaction layers.With increase of the melt superheating degree and the slower of cooling rate
the thickness of IMC formed at solder/Cu is increased.The reaction layers formed at the Sn-9Zn/Cu and Sn-3.5Ag-0.7Cu/Cu interfaces are affected by the melt superheating degree and cooling rate more greatly than that of Sn-37Pb/Cu.During aging process
there exists a mutual competition between the decomposition of Cu-Zn compound layer and the growth of CuZn-Sn compound layer
resulting in the irregular change of IMC layer thickness of the air-cooled Sn-9Zn/Cu.The mechanisms of the formation of IMC layer and its changes during aging were described.