Xiaowu Hu

Shear strength and fracture surface analysis of Sn58Bi/Cu solder joints under a wide range of strain rates

Abstract The influences of the strain rate on the shear strength and failure mode of Sn58Bi/Cu solder joints were investigated. After reflowing, some Kirkendall voids were observed at the neighborhood of the Cu3Sn/Cu interface or in the inner Cu3Sn layer. In addition, another type of void could also be observed inside the Sn58Bi eutectic solders, and its size was much larger than that of Kirkendall voids. Some Bi particles were obviously found to segregate at the interface between the Cu-Sn IMC and the Sn58Bi solder. The single lap shear test results indicated that the strain rate had an important influence on the shear strength and failure mode of Sn58Bi/Cu solder joints. The shear strength of joints demonstrated increment at first and then decrement as the strain rate increased from 3.33 × 10−4 s−1 to 3.33 s−1. It was observed that all Sn58Bi/Cu solder joints broke in a mixed-type fracture mode under a wide range of strain rates. Additionally, more broken IMC grains were exposed on the fracture face and more fracture occurred within the IMC layer with increasing strain rate. Furthermore, the fracture path gradually moved from the solder side to the inner IMC side as the strain rate increased.

Interfacial Reaction and IMC Growth of an Ultrasonically Soldered Cu/SAC305/Cu Structure during Isothermal Aging

In order to accelerate the growth of interfacial intermetallic compound (IMC) layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic soldering. The isothermal aging was conducted at 150 °C for 0, 120, 240, and 360 h. The evolution of microstructure, the IMC layer growth mechanism during aging, and the shear strength of the joints after aging were systemically investigated. Results showed the following. (i) Formation of intermetallic compounds was accelerated by ultrasonic cavitation and streaming effects, the thickness of the interfacial Cu6Sn5 layer increased with aging time, and a thin Cu3Sn layer was identified after aging for 360 h. (ii) The growth of the interfacial IMC layer of the ultrasonically soldered Cu/SAC305/Cu joints followed a linear function of the square root of the aging time, revealing a diffusion-controlled mechanism. (iii) The tensile shear strength of the joint decreased to a small extent with increasing aging time, owing to the combined effects of IMC grain coarsening and the increase of the interfacial IMC. (iv) Finally, although the fracture surfaces and failure locations of the joint soldered with 400 ms and 800 ms vibration times show similar characteristics, they are influenced by the aging time.

Effect of electroplating parameters on electroplated Cu film and microvoid formation of solder joints

The influences of electroplating parameters on electroplated Cu (EPC) film and void formation at the Sn3.0Ag0.5Cu (SAC305)/Cu interface were investigated. It is found that the size of Cu particles increased with the increase of current density or deposit thickness. The surface roughness of Cu films also increased with increasing current density. And the surface roughness of EPC films demonstrated decrement at first and then increment with the increase of deposit thickness. It is observed that the electrodeposition with higher current density or thicker Cu film tended to inhibit the growth of Cu(111) and favor the growth of Cu(220). After reflowing and thermal aging, the voiding level increased greatly as the current density and deposit thickness increased, and that total microvoid area increased gradually with increasing aging time for all electroplating conditions. Additionally, the variation in the current density and deposit thickness did not influence the intermetallic compound growth rate.