  Interfacial reactions and shear properties of the In-48Sn (in wt.%) ball grid
array (BGA) solder joints after bonding were investigated with four different
surface finishes of the substrate over an underlying Cu pad: electroplated
Ni/Au (hereafter E-NG), electroless Ni/immersion Au (hereafter ENIG), immersion
Ag (hereafter I-Ag) and organic solderability preservative (hereafter OSP).
During bonding, continuous AuIn2, Ni3(Sn,In)4 and Cu6(Sn,In)5 intermetallic
compound (IMC) layers were formed at the solder/E-NG, solder/ENIG and
solder/OSP interface, respectively. The interfacial reactions between the
solder and I-Ag substrate during bonding resulted in the formation of
Cu6(Sn,In)5 and Cu(Sn,In)2 IMCs with a minor Ag element. The In-48Sn/I-Ag
solder joint showed the best shear properties among the four solder joints
after bonding, whereas the solder/ENIG solder joint exhibited the weakest
mechanical integrity.
