T. Ogashiwa et A. Inoue, CHARACTERISTICS OF RAPID SOLIDIFIED PB-SN ALLOY WIRES AND THEIR APPLICATION TO SOLDER BUMP FOR FINE JUNCTION, Nippon Kinzoku Gakkaishi, 58(8), 1994, pp. 944-951
A new solder bump formation method using a wire bonding machine, which
was named as a solder bumping method, was developed by the use of a r
apidly solidified 97.9Pb-2Sn-0.05Sb-0.05Cu wire. The most important fu
nction of the wire for the bump formation is fracturing at a constant
site which enables the formation of balls with a constant size. In ord
er to evaluate the fracture site of the wire, the ratio of the tensile
proportional limit (sigma(p)) in the as-rolled state to 75-97% reduct
ions in area to the ultimate tensile strength in the annealed state fo
r 60 s at 571 K was investigated for the cast alloys obtained at diffe
rent cooling rates. The rapid solidification and subsequent cold rolli
ng processes cause the increase in sigma(p)(as-rolled), resulting in t
he increase in the ratio of sigma(p)(as-rolled)/sigma(u)(annealed). Th
e addition of 0.05%Cu was necessary to keep high values of sigma(p)(as
-drawn)/sigma(u)(annealed) exceeding 1.0. The scattering of the shape
and size of the bump after reflowing treatment for 60 s at 623 K were
small enough to be put the solder bump material and the bump formation
process into practical application.