Patent Number: 7,784,669

Title: Method and process for reducing undercooling in a lead-free tin-rich solder alloy

Abstract: Briefly, a novel material process is disclosed wherein one or more nucleation modifiers are added, in trace amounts, to a lead-free tin-rich solder alloy to produce a solder composition with reduce or suppressed undercooling temperature characteristics. The modifier being a substance which facilitates the reduction of extreme anisotropic properties associated with body-centered-tetragonal tin based lead-free solder. The addition of the nucleation modifiers to the solder alloy does not materially effect the solder composition's melting point. As such, balls of solder with the nucleated composition freeze while other solder balls within the array remain in the melt. This effectively enables one substrate to be pinned to another substrate by one or more predetermined solder balls to secure the package while the remaining solder joints are in the liquid state. Further, the addition of a trace amount of nucleation sites within the composition facilitates control over the number, size, and orientations of primary intermetallic compounds in tin rich crystallite grains. Moreover, trace amounts of one or more solid and/or insoluble nucleating modifiers within a given volume of solder reduces the size of average crystallites within the composition.

Inventors: Hougham; Gareth G. (Ossining, NY), Srivastava; Kamalesh K. (Wappingers Falls, NY), Kang; Sung K. (Chappaqua, NY), Shih; Da-Yuan (Poughkeepsie, NY), Sundlof; Brian R. (Verbank, NY), Chey; S. Jay (Ossining, NY), Henderson; Donald W. (Ithaca, NY), Di Milia; David R. (Wappingers Falls, NY), Ferlita; Richard P. (Wappingers Falls, NY), Carruthers; Roy A. (Stormville, NY)

Assignee: International Business Machines Corporation

International Classification: B23K 35/24 (20060101)

Expiration Date: 8/31/12018