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This study investigated the influence of substrate metallization on the microstructure and creep behavior of the pure tin solder joints. Both symmetric (Cu:Cu) and the asymmetric (Cu:Au/Ni) metallizations were tested. The solder joints with asymmetric substrates had lower creep rates than those with symmetric (Cu:Cu) substrates. (Cu-Ni)6Sn5 intermetallics formed on all substrates. However, a dramatic and anomalous intermetallic growth was observed on the Ni-side of the asymmetric joints; after typical reflow the intermetallic reached almost one third of the solder joint thickness. It appears that the abnormally thick intermetallic inhibits creep in the asymmetric joint and is the primary cause of the lower creep rates.
Date of Conference: 16-18 March 2005