Abstract
Dynamic observation of the microstructure evolution of Sn2.5Ag0.7Cu0.1RE/Cu solder joints and the relationship between the interfacial intermetallic compound (IMC) and the mechanical properties of the solder joints were investigated during isothermal aging. The results showed that the original single scallop-type Cu6Sn5 IMC gradually evolved into a planar double-layer IMC consisting of Cu6Sn5 and Cu3Sn IMCs with isothermal aging. In particular, the Cu3Sn IMC grew towards the Cu substrate and the solder seam sides; growth toward the Cu substrate side was dominant during the isothermal aging process. The growth of Cu3Sn IMC depended on the accumulated time at a certain temperature, where the growth rate of Cu3Sn was higher than that of Cu6Sn5. Additionally, the growth of the interfacial IMC was mainly controlled by bulk diffusion mechanism, where the activation energies of Cu6Sn5 and Cu3Sn were 74.7 and 86.6 kJ/mol, respectively. The growth rate of Cu3Sn was slightly faster than that of Cu6Sn5 during isothermal aging. With increasing isothermal aging time, the shear strength of the solder joints decreased and showed a linear relationship with the thickness of Cu3Sn. The fracture mechanism of the solder joints changed from ductile fracture to brittle fracture, and the fracture pathway transferred from the solder seam to the interfacial IMC layer.
Highlights
In an electronic packaging system, solder joints provide an electrical connection and mechanical support to the electronic components
The solder alloy and Cu substrate were prepared according to the procedures described in reference [30]
The solder joints consisted of a soldering seam, interfacial intermetallic compound (IMC), and Cu substrate
Summary
In an electronic packaging system, solder joints provide an electrical connection and mechanical support to the electronic components. The need for function integration, high power, and density of the electronic products has been a driving force for highly reliable inter-connection solder joints [1,2]. Because of the inherent toxicity of lead, the use of SnPb solder has been restricted. Various types of environmental-friendly Sn-based lead-free alloys have been developed [3–7]. SnAgCu system lead-free solder alloys have been regarded as one of the promising candidates for SnPb solder alloys because of their good mechanical properties [8]. Compared to the traditionally SnPd solders, the wettability SnAgCu lead-free solders are relatively poor.
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