Intermetallic reactions in reflowed and aged Sn-58Bi BGA packages with Au/Ni/Cu pads
Journal
Journal of Materials Engineering and Performance
Journal Volume
17
Journal Issue
1
Pages
134-140
Date Issued
2008
Author(s)
Abstract
The reflow of Sn-58Bi solder joints in a BGA package with Au/Ni/Cu pads has been performed by employing various temperature profiles, which results in the formation of (Au 0.66Ni 0.34)(Sn 0.82Bi 0.18) 4 intermetallic flakes in the solder matrix. The reflow operation performed at a peak temperature of 180 °C for a melting time of 80 s gives a ball shear strength of 9.1 N, which decreases drastically to lower values between 6.4 and 4.6 N after further aging at temperatures from 75 to 125 °C. Double layers of intermetallic compounds with the compositions of (Au 0.30Ni 0.70)(Sn 0.90Bi 0.10) 4/Ni 3Sn 4 can be found at the solder/pad interfaces of the aged Sn-58Bi solder joints. Ball shear testing of the reflowed specimens shows ductile fracture through the solder matrix, which changes to brittle cleavage fracture mainly along the (Au 0.30Ni 0.70)(Sn 0.90Bi 0.10) 4 intermetallic layer after aging at various temperatures. The measurement of ball shear strengths (S) reveals a linear relation with the thicknesses (X) of (Au 0.30Ni 0.70)(Sn 0.90Bi 0.10) 4 intermetallic layers: S = 7.13 - 0.33X. © 2007 ASM International.
Type
journal article