Volume effect on the soldering reaction between SnAgCu solders and Ni

Abstract

The diameters of the solder joints in the array-array packages can range from 760 /spl mu/m (BGA joints) to 75 /spl mu/am (flip-chip joints). This variation in diameter in fact translates into a 1,000 times difference in volume. Such a large difference in volume produces a pronounced solder volume effect. In this study, the volume effect on the liquid-solid reactions between the Sn3AgxCu (x = 0.4, 0.5, or 0.6 wt.%) solders and Ni was investigated. Three different sizes of solder spheres (760 /spl mu/m, 500 /spl mu/m, and 300 /spl mu/m) were soldered on 400 /spl mu/m diameter electrolytic Ni soldering pads for 90 sec-20 min at a peak reflow temperature of 235/spl deg/C. Two reaction products (Cu,Ni)/sub 6/Sn/sub 5/ and (Ni,Cu)/sub 3/Sn/sub 4/ were present at the interface in all the samples. Interestingly, a massive spalling of (Cu,Ni)/sub 6/Sn/sub 5/ from the interface occurred, especially in samples with smaller solder balls and lower Cu concentration. We attributed the massive spalling of (Cu,Ni)/sub 6/Sn/sub 5/ to the decrease in the amount of available Cu in the solders as the amount of solder as well as the Cu concentration decreased. The results of this study suggested that a high Cu-content SnAgCu solder should be used to prevent this massive spalling.