Abstract
The microstructural properties of a Pb-free solder joint significantly affect its mechanical behaviours. This paper details a systematic study of the effect of the annealing process on the microstructure and shear strength of a Zn-added Sn-0.7Cu solder joint. The results indicated that the IMC layer’s thickness at the solder/Cu interface increases with annealing time. The interfacial IMC layer of the Sn-0.7Cu solder joint gradually thickened with increasing annealing time and annealing temperature, while the interfacial IMC layer’s morphology changed from scallop-type to layer-type after the annealing process. However, the addition of 1.0 wt.% and 1.5 wt.% Zn in the Sn-0.7Cu effectively altered the interfacial IMC phase to Cu-Zn and suppressed the growth of Cu3Sn during the annealing process. The single-lap shear tests results confirmed that the addition of Zn decreased the shear strength of Sn-0.7Cu. The interfacial IMC of the Cu6Sn5 phase in Sn-0.7Cu changed to Cu-Zn due to the addition of Zn. The shear fractures in the annealed solder joint were ductile within the bulk solder instead of the interfacial IMC layer. Increased annealing time resulted in the increased presence of the Cu-Zn phase, which decreased the hardness and shear strength of the Sn-0.7Cu solder joint.
Highlights
The traditional Sn-Pb solder is prevalent in interconnections and electronic packaging
Sn-0.7Cu is one of the most common Pb-free solders used in electronic packaging due to its excellent mechanical properties, wettability, ubiquity, and low costs [2]
In the electronic packaging industry, reliability losses in many electronic systems are caused by the failure of solder joints instead of device malfunction [3], which shifted research focus onto solder joints’ reliability
Summary
The traditional Sn-Pb solder is prevalent in interconnections and electronic packaging.its toxicity and environmental impact are of grave concern. Several iterations of Pb-free solders, such as Sn-Ag, Sn-Zn, Sn-Ag-Cu, and Sn-Cu solder systems, have been developed to pursue green technologies in electronics manufacturing. Sn-0.7Cu is one of the most common Pb-free solders used in electronic packaging due to its excellent mechanical properties, wettability, ubiquity, and low costs [2]. In the electronic packaging industry, reliability losses in many electronic systems are caused by the failure of solder joints instead of device malfunction [3], which shifted research focus onto solder joints’ reliability. Solder joint reliability studies commonly involve a crucial component: the interfacial intermetallic compounds (IMCs). Interfacial intermetallic layer(s) form at the solder/Cu interfaces when the solder wets the Cu pad on the PCB, which subsequently dictates the bonding strength and service reliability of the solder joints
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