Sn-xAg-0 7Cu無鉛銲料微結構與低週疲勞研究

Abstract

This research is aimed to investigate the effect of Ag content (0~3 Wt.%) on the pasty range and microstructure of Sn-Ag-Cu lead-free solder. The Low-cycle fatigue properties of the solder joints at diffirent temperature conditions (25, 80, 120℃) were evaluated. Sn-xAg-0.7Cu solder in form of solder balls with 1.1±0.02 mm in diameter were fabricated. Solder balls were re-flowed with Cu substrate in the form of single lap shear specimen, and then the Low-cycle fatigue test were performed. Experimental results show that when Sn-0.7Cu alloy is added Ag, the solidus point will decrease. However, it will not change when more Ag is added. The gap between solidus and liqiudus temperature (Pasty range) will reduce with more addition of Ag. The microstructure of Sn-xAg-0.7Cu alloys consists of plate-like Ag3Sn intermetallic compounds, together with the copper present as rod-like Cu6Sn5 within a β-Sn matrix for all alloys. The increase in silver content may enhance the hardness of the solder alloy as a result of an increase in volume fraction of Ag3Sn intermetallics.The matrix of Sn-0.7Cu consists of β-Sn equiaxial grains and small particles of Cu6Sn5 that have not significantly influence on the hardness of solder. In the condition with constant displacement of 0.025mm, shear strength of the solder joints is increased with higher Ag additions. In the diffirent temperature conditions, Fatigue life of the solder joint approximately increases with greater Ag additions. The reason is the plastic displacement of the solder joint decreases with higher Ag additions, and the lesser plastic displacement the better fatigue life. However, The fracture modes of Sn-3.0Ag-0.7Cu alloy is mixture mode at 25 ℃, and the mixture mode will decrease fatigue life by fracturing in IMC layer and solder. In this research, III the fracture mode of all the alloys are solder fracture mode at 80℃ and 120℃. Beacuse the alloys have influnces on creep behavior which decrease the fatigue properties of solder joints. With compare of pasty range, microstructure and fatigue life of Sn-xAg-0.7Cu solder. The solder contains 1.5 Wt.% Silver has better behaviors.