Solder metallization interdiffusion in microelectronic interconnects

Shear strength and aging characteristics of 63Sn−37Pb solder bumps with various solder ball and pad sizes

“…It has been known that Au rapidly dissolves in the 63Sn-37Pb solder during reflow on Au/Ni/Cu UBM due to its high solubility and interact with Sn to form IMC, AuSn 4 [3,[8][9][10][11]. When the solder bumps are aged at 150 o C, AuSn 4 compounds migrate to the Ni 3 Sn 4 layer and form a ternary intermetallic phase (Au,Ni)Sn 4 at the Ni 3 Sn 4 /solder interface, causing degradation in the solder joint strength with brittle fracture throughout the intermetallic compounds [8][9][10].…”

“…For the solder bumps reflowed on Au/Ni/Cu as well as Ni/Cu, Ni 3 Sn 4 was formed at the solder/UBM interface. As the solubility limit of Au is very high (about 7 %) in the molten 63Sn-37Pb solder at 220 o C [9], 0.5 µm-thick Au layer was dissolved completely into the molten solder during reflow, exposing the Ni layer to the molten solder. The Au dissolution rate to the molten eutectic Sn-Pb was estimated as 1.78 µm/sec, and the 0.5 µm-thick Au layer of Au/Ni/Cu would disappear completely within 0.2 sec during reflow [9].…”

“…As the solubility limit of Au is very high (about 7 %) in the molten 63Sn-37Pb solder at 220 o C [9], 0.5 µm-thick Au layer was dissolved completely into the molten solder during reflow, exposing the Ni layer to the molten solder. The Au dissolution rate to the molten eutectic Sn-Pb was estimated as 1.78 µm/sec, and the 0.5 µm-thick Au layer of Au/Ni/Cu would disappear completely within 0.2 sec during reflow [9]. When the 63Sn-37Pb solder was reflowed on Ni foils at 220 o C, the growth rate of Ni 3 Sn 4 was reported as 0.72×10 −3 mm/sec [13], which is in good agreement with the approximate 0.64×10 −3 mm/sec obtained on Au/Ni/Cu UBM in this study.…”

“…The Au layer is plated to improve the solder wettability and to protect Ni from corrosion before reflow. However, Au plating has been reported to have a detrimental effect on the reliability of the solder joints, i.e., degradation of shear strength by thermal aging and thermal fatigue tests [3,[8][9][10][11]. Although some work has been done to figure out the effect of Au plating thickness on the shear strength degradation [8,11], the relationship between the aging characteristics of the solder bumps and the bump shape, which is determined by the relative sizes of the solder ball and UBM pad, has been little reported.…”

Mechanical Properties and Shear Strength of Sn-3.5Ag-Bi Solder Alloys

“…Such increase in the shear strength could be related to dissolution of Ni in Au/Ni/Cu UBM to the solder during reflow. As reported for 63Sn-37Pb reflow, 12) Au layer in Au/Ni/Cu UBM is dissolved completely into Sn-3.5Ag during reflow, exposing Ni layer to the molten solder. 13,14) Contrary to low solubility limit of Ni, 0.052 at%, in 63Sn-37Pb at 220…”