Thermodynamics and Kinetics of Oxidation and Temperature Dependent Mechanical Characterization of Pure Indium Solder

MicroElectroMechanical System (MEMS) devices often require low-temperature, fluxless soldering techniques due to their high temperature sensitivity and the performance requirements of specific components. While seeking the development of a soldering technology using pure indium, the major focus of this study is to assess the thermodynamics and kinetics of indium oxidation at various solder reflow environments that will ultimately provide a processing window for solder reflow and surface oxide cleaning. The stability of oxidation and reduction reactions for indium is presented in terms of several thermodynamic models. The influence of pO2, pH2O, pH2, pCO, pCO2 on the location of oxidation and reduction zones is calculated using reaction equilibrium. Due to temperature limitations during processing of electronic packaging materials, pH2O was found to be the critical parameter in creating a reducing environment using a hydrogen reaction. Additionally, because of the large enthalpy associated with the formation of In2O3, pO2 was found to have little influence on thermodynamic equilibrium in both H2(g) and CO(g) reducing reactions. Verification of the thermodynamic models is carried out by oxidation experiments performed in various environments. With a glove box employed for precise atmospheric control, pH2O, pO2, and pH2 are varied to examine their effects on the oxidation and reduction behavior of indium. We also explore oxidation mechanisms at different stages of oxide growth, as well as at different regimes of temperature from 145 ̊C-220 ̊C. In particular, electron transport from indium to indium oxide is shown to be the rate