Creep of two lead-free high temperature solder alloys, 95Sn-5Ag and 99Sn-1.0Cu was studied in this investigation. Room and high temperature creep tests were performed to examine deformation mechanisms and to establish mathematical models of creep deformation for the alloys. A state variable creep model was introduced to model both primary and secondary creep deformation of these two alloys which show a very significant primary creep. Fatigue life models of the alloys were established based on an energy-based failure criteria, which was deduced from variable strain amplitude tests at a constant strain rate of 0.003/sec, and from variable strain rates tests with two constant strain amplitudes of 0.005 and 0.01. Applications of the creep model includes determination of peak loads and hysteresis strain energy density in strain-controlled fatigue tests. It is demonstrated that the creep model can be very helpful to establish fatigue failure criteria and to assess fatigue lives of these two alloys.

Compatibility and characteristics of multilayer dielectric thick films with Cu interlayers are influenced by composition and processing parameters. In this work, cordierite based dielectric thick films on a Cu plated alumina substrate were investigated in terms of microstructure and property by changing composition of oxide additives, PbO and Cu2O for a given heating schedule. A nonstoichiometric cordierite composition, 2.4MgO 2Al2O3 5SiO2 was used with nucleating agents, B2O3 and P2O5. The dielectric ink consisting of cordierite glass frit and acrylic based binder vehicles was deposited on oxidized Cu layers via screen printing. The thick film layers were fired at 950°C for 30 min in N2 atmosphere. Dissolution of the oxidized Cu into the cordierite layer was observed. The addition of a small amount of Cu2O to the cordierite layer was effective in preventing the dissolution and enhancing thermal expansion. Crystallization was also influenced by the Cu2O addition. A lower activation energy value of 79 kcal/mol for crystallization, calculated from DTA runs, suggested that Cu20 could be used to form the cordierite glass-ceramic at a lower temperature. In the case of no additive, the activation energy for crystallization was 98 kcal/mol. The addition of Cu2O increased dielectric constant. For 3wt% PbO and 1wt% Cu2O, the dielectric constant and loss were determined at 1 MHz as 6.1 and 0.0046, respectively.