Reaction Between Thin Gold Wires and Pb-Sn-In Solder (37.5%, 37.5%, 25%), Part A: The Radial Reaction Inside The Solder Mounds, Its Linear Reaction Model, Statistical Variation of Reaction Rate, and Induced Structural Changes In The Solder Mounds.

Abstract

Thermodynamics favors the reaction between indium and gold, since the heat of formation of AuIn{sub 2} is 6 kcal/mole, substantially larger than the heat of formation of any other possible reaction product. Thermodynamic equilibrium between gold and the elements in the solder mound is reached only when ALL gold is converted to AuIn{sub 2}. There are two aspects to this conversion: (A) the reaction WITHIN the solder mound (called here 'radial reaction') and (B) the reaction OUTSIDE the solder mound (called here 'axial reaction') and the transition from (A) to (B). The reaction between thin gold detonator wires and the In/Pb/Sn solder mound in older detonators has been looked at repeatedly. There are, in addition, two studies which look at the reaction between indium and gold in planar geometry. All data are shown in tables I to V. It is the objective of this section dealing with aspect (A), to combine all of these results into a reaction model and to use this reaction model to reliably and conservatively predict the gold-solder reaction rate of soldered gold bridge-wires as a function of storage temperature and time.