Abstract
The shear performance and fracture behavior of microscale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with increasing electric current density (from 1.0 × 103 to 6.0 × 103 A/cm2) at various test temperatures (25 °C, 55 °C, 85 °C, 115 °C, 145 °C, and 175 °C) were investigated systematically. Shear strength increases initially, then decreases with increasing current density at a test temperature of no more than 85 °C; the enhancement effect of current stressing on shear strength decreases and finally diminishes with increasing test temperatures. These changes are mainly due to the counteraction of the athermal effect of current stressing and Joule heating. After decoupling and quantifying the contribution of the athermal effect to the shear strength of solder joints, the results show that the influence of the athermal effect presents a transition from an enhancement state to a deterioration state with increasing current density, and the critical current density for the transition decreases with increasing test temperatures. Joule heating is always in a deterioration state on the shear strength of solder joints, which gradually becomes the dominant factor with increasing test temperatures and current density. In addition, the fracture location changes from the solder matrix to the interface between the solder matrix and the intermetallic compound (IMC) layer (the solder/IMC layer interface) with increasing current density, showing a ductile-to-brittle transition. The interfacial fracture is triggered by current crowding at the groove of the IMC layer and driven by mismatch strain at the solder/IMC layer interface, and the critical current density for the occurrence of interfacial fracture decreases with increasing test temperatures.
Highlights
Solder joints provide electrical, thermal, and mechanical connections among different components and various circuits in electronic products and devices, which are considered the weakest link in electronics [1]
Once current is applied to a solder joint, Joule heating alters the thermal condition; the shear stress generates at the interfaces owing to the coefficient of thermal expansion (CTE) mismatch between different materials in the solder joint [2]
The fracture location changes from the solder matrix to the cathode interface with a ductileto-brittle transition [11,12,13]. Both Joule heating and the athermal effect of current stressing have a significant influence on the shear performance and fracture behavior of solder joints
Summary
Thermal, and mechanical connections among different components and various circuits in electronic products and devices, which are considered the weakest link in electronics [1]. The fracture location changes from the solder matrix to the cathode interface with a ductileto-brittle transition [11,12,13] Both Joule heating and the athermal effect of current stressing have a significant influence on the shear performance and fracture behavior of solder joints. Joule heating and the athermal effect of current stressing are usually applied to in-service solder joints simultaneously. When a low current density of 7.0 × 102 A/cm is applied to the single-interface SAC105/Cu solder joints, the shear strength of solder joint under current stressing is about 9.5% higher than that at a corresponding TJoule [28] This indicates that the athermal effect of current stressing may enhance shear performance. The influences of Joule heating and the athermal effect on the shear strength of solder joints were decoupled and quantified for a thorough discussion
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