Investigations on Mechanical Properties, Wettability and Aging of Sn-Zn-Ag-Al Lead-Free Solders

• Main Authors: Shou-Chang Cheng, 鄭壽昌
• Other Authors: Kwang-Lung Lin
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/84062317687917726853

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 92 === 　　The microstructure, mechanical property, wettability and interfacial reaction of Sn-Zn system lead-free solders including eutectic Sn-9Zn, Sn-Zn-1Ag, and Sn-Zn-1Ag-XAl (X=0.01~0.45wt%) were investigated. 　　Microstructure of Sn-Zn-1Ag shows needle-like Zn-rich phase, dendrite ε-AgZn3 compound and hypo-eutectic phase in matrix, then the Sn-Zn eutectic structure and β-Sn phase. Those of the Sn-Zn-1Ag-XAl solder alloys consist of AgZn3 compound, Zn-rich phase, Al-rich segregation and hypo-eutectic phase. The addition of Al dramatically improves the 0.2% offset yield stress, Vicker's hardness, ultimate tensile stress, and total tensile strain of the Sn-Zn-1Ag-XAl alloys. The increase in Al content of Sn-Zn-1Ag-XAl alloy from 0.01 to 0.45wt% increases the yield stress from 49.9 to 54.0MPa (~ 47.6MPa for eutectic Sn-9Zn) and the Vicker's hardness values from 17.0 to 18.3Hv (~16.8Hv for eutectic Sn-9Zn). The UTS of Sn-Zn-1Ag-XAl alloys with X=0.01, 0.1, 0.25, and 0.45wt% Al, are respectively 55, 58, 55, and 60 MPa, while the tensile strains are respectively 47%, 52%, 58%, and 45% (52MPa and 50% for eutectic Sn-9Zn). Fracture mechanisms of the Sn-Zn-1Ag-XAl alloys are correlated with the existence of Zn-rich phase and Al segregation. 　　The wetting behaviors between the Sn-Zn-1Ag-XAl alloys and Cu have been investigated with the wetting balance method. The results of DSC analysis indicate that the solders exhibit a solid-liquid coexisting range of about 7~10°C. The solidus temperature of the Sn-Zn-1Ag-XAl alloys are within 197~198°C, while the liquidus temperature are within 205~207°C. The experimental results showed that the wettability of the Sn-Zn-1Ag-XAl alloys is improved by the addition of Al. The maximum wetting force of the alloys with Cu is within 0.75~1.18mN and the wetting time is around 1.0~1.1 seconds, better than those of eutectic Sn-9Zn and Sn-Zn-1Ag alloys. The addition of Al also depresses the formation ofε-AgZn3 compound at the interface between Sn-Zn-1Ag-XAl and Cu. 　　For interfacial reaction after aging, the experimental results showed that the interface between Sn-9Zn and Cu resulted in voids and crack when aged at 150°C for 1000 hours. The Cu-rich/ Cu3(Zn,Sn)/Cu6(Sn,Zn)5 IMC layer was observed at the interface. When aged for 1700 hours, the Cu3(Zn,Sn)/Cu6(Sn,Zn)5 layer was also been detected and the Kirkendall voids and crack was observed at the interface between Sn-Zn-1Ag and Cu. Cracks formed upon extending aging for 1000 hours at the solder/IMC interface or within IMC layer for the following solders: Sn-9Zn, Sn-Zn-1Ag, Sn-Zn-1Ag-0.1Al, Sn-Zn-1Ag-0.25Al, and Sn-Zn-1Ag-0.45Al. The Sn-Zn-1Ag-0.01Al/Cu couple exhibited no crack up to aging time of 3000 hours. The Cu3(Zn,Sn)/Cu6(Sn,Zn)5 layer was also formed at the interface between Sn-Zn-1Ag-XAl and Cu.