Effect of Cooling Rate on the Microstructural and Mechanical Properties of Sn-0.3Ag-0.7Cu-0.05Ni Solder Alloy

The effect of cooling rate on the microstructural and mechanical properties of Sn-0.3Ag-0.7Cu-0.05Ni lead-free solder alloy was studied. The microstructure of specimens was characterized by using an optical microscope (OM) and an energy dispersive X-ray spectroscopy (EDX). The mechanical properties were performed by using a universal testing machine (UTM). The results showed that the cooling rate of water-cooled specimens was about 2.37 °C/s and the cooling rate of mold-cooled specimens was about 0.05 °C/s. To compare the different cooling rates, it was found that the grain size of water-cooled specimens was finer than that of the mold-cooled specimens, this resulted in an increment of mechanical properties of solder alloy. A higher tensile strength (33.10 MPa) and a higher elongation (34%) were observed when water-cooled and mold-cooled systems were used, respectively. The microstructure of Sn-0.3Ag-0.7Cu-0.05Ni lead-free solder alloy solidified by both cooling systems exhibited three phases: β-Sn, Ag3Sn and (Cu,Ni)6Sn5 IMCs.

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Experimental Investigation of the Effect of Reflow Cooling Rate on the IMC Growth of SAC Lead-Free Solder Alloy

Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology ◽

10.1115/imece2005-82095 ◽

2005 ◽

Cited By ~ 3

Author(s):

Fubin Song ◽

S. W. Ricky Lee

Keyword(s):

Mechanical Properties ◽

Cooling Rate ◽

Solder Alloy ◽

Room Temperature ◽

Solder Ball ◽

Ternary Eutectic ◽

Lead Free ◽

Lead Free Solder ◽

Lead Free Solder Alloy ◽

Free Solder

The present research is conducted to investigate a critical issue for Lead-free solder alloy. Near-ternary eutectic Sn-Ag-Cu alloys have been studied since they are the leading Lead-free candidate solders for various applications. There are three main phases in the near-ternary eutectic alloys: β-Sn rich phase, Ag3Sn and Cu6Sn5. Cooling rate is an important processing factor that affects the microstructure of these alloys and then significantly influences mechanical behavior of the Sn-Ag-Cu solder joints. It is demonstrated that the amount and size of large Ag3Sn plates increase with decreasing of the cooling rate. When large Ag3Sn plates present in the solder joints at the lower cooling rate, they may affect the mechanical integrity of the joints by providing a crack initialization during the mechanical testing under room-temperature condition. In the present paper, the effects of cooling rate on the microstructure and mechanical properties are studied on Sn-3.8Ag-0.7Cu solder ball, including shear strength and ball pull test. There are two kinds of fracture mode for Ag3Sn plates preformed mechanical loading in room-temperature condition. One is brittle fracture inside Ag3Sn plate itself; the other is interfacial fracture of Ag3Sn plates and the IMC layer. Moreover, the fractures of large Ag3Sn plates induce the decrease of mechanical properties on Sn-3.8Ag-0.7Cu solder ball. The critical cooling rate of large Ag3Sn plate formation is also investigated.

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