Reliability of Sn-Ag-Sb lead-free solder joints

The effect of Sb contents (0-10 wt%) on the reliability of Sn-Ag-Sb solder has been investigated with isothermal low cycle mechanical fatigue tests. The solders tested were Sn-3.5Ag with Sb contents of 1.73, 3.85, 5.12 and 10.05 wt%, respectively, in the form of solder balls. Single-lap specimens were used to simulate real solder joints with the solder balls reflowed between two pure Cu substrates. Experimental results showed that under a fixed controlled displacement of 0.025 mm, fatigue life of the as-soldered joint increased with the amount of Sb additions due to less plastic strain the hardened solders produced. Load drop rate in the final stage increased as Sb addition increased. Fatigue cracks initiated at locations between the neck of the hourglass-shaped solder joint and the intermetallic compound (IMC) layer formed between the solder and copper. With the increase of Sb contents, the fracture mode evolved from within the bulk solder to a mixed fracture mode of solder and IMC layer, and finally, along the IMC layer.