Publications

Pull strength and failure mode analysis of thick film conductors on alumina ceramic for hybrid microcircuit technologies

Vianco, Paul T.; Rejent, Jerome A.; Kilgo, Alice C.; Zender, Gary L.

Thick film conductors provide the circuitry for hybrid microcircuit (HMC) assemblies. The integrity of solder joints made to those conductors is a function of the solid-state interface reactions that occur under long-term service environments. A study was performed, which examined the mechanical strength of 63Sn-37Pb (wt.%, Sn-Pb) solder joints made to the thick film conductor, 76Au-21Pt-3Pd (Au-Pt-Pd), on 96% Al2O3 substrates. The Au-Pt-Pd layer was 18±3 μm thick. Isothermal aging accelerated the solder/thick film interface reaction, which resulted in the growth of an intermetallic compound (IMC) layer and consumption of the thick film layer. The aging temperatures were 70°C, 100°C, and 135°C. The aging times were 5-5000 hours. The sheppard's hook pull test was used to assess the strength of the Sn-Pb solder joints at two displacement rates: 10 mm/min and 100 mm/min. A measurable loss of joint strength was observed after aging, which did not generate a great deal of IMC layer growth. The aging effects occurred at the thick film/Al2O3 interface as concluded by other authors. However, the present investigation showed those strength losses to be reversible after more extended aging times at elevated temperature. The strength and failure modes were sensitive to displacement rate when IMC layer development was minimal. Extensive growth of the IMC layer was accompanied by the formation of a Pb-rich layer ahead of it, which was responsible for a gradual decrease in the pull strength. In this case, pull strength and failure mode were less sensitive to displacement rate. The solder joints maintained a nominal level of pull strength, even after nearly all of the thick film conductor had been consumed by IMC layer formation. Copyright © 2010 MS&T'10®.