|Institution:||Helsinki University of Technology; Teknillinen korkeakoulu|
|Department:||Department of Electrical and Communications Engineering|
|Keywords:||Electrical engineering; reliability; solder interconnection; thermal modelling; thermodynamic calculation; kinetics; interfacial reaction|
|Full text PDF:||https://aaltodoc.aalto.fi/handle/123456789/2791|
Continuous miniaturization of electronics devices as well as increasing complexity of soldering metallurgy introduce more and more challenges to the reliability of modern electronics products. Although loading condition plays an important role, the reliability of solder interconnections is ultimately controlled by microstructures' responses to loading. It is therefore of great importance to understand and control the microstructural evolutions of solder interconnections under different loading conditions. Since experimental investigation alone is inadequate for achieving such knowledge, the employment of different modeling tools is of great help. In this thesis, combined usage of thermal, thermodynamic and kinetic modelling was introduced and utilized in studying solidification and interfacial reactions in solder interconnections. In order to study the solidification of interconnections during reflow soldering, an oven-level thermal model was first constructed to simulate the flow field inside a typical reflow oven. With the oven information collected, the thermal models were established to simulate the solidification of lead-free solder interconnections. Thermodynamic calculations, which were integrated into the model, provided the thermal properties of the solder alloy used in the experiments. Further, thermodynamic calculations were combined with the nucleation kinetic analyses to evaluate the actual solidification temperatures of interconnections. The combined thermodynamic and kinetic approach was used also for studying the interfacial reactions between solder and component or board metallizations. For having better understanding of the effect of Ni in solder interconnections, the Sn-Cu-Ni system was assessed thermodynamically. Firstly, the effect of Cu-content on the formation of the primary interfacial intermetallic compounds between near-eutectic SnAgCu solder alloys and Ni-substrate was evaluated as a function of temperature. Secondly, it was analyzed how the Ni dissolved in Cu6Sn5 compound affects the driving forces for the diffusion fluxes and hence the growth kinetics of (Cu,Ni)6Sn5 and (Cu,Ni)3Sn reaction layers between near-eutectic SnAgCu solder and Cu(Ni) metallizations. With the preliminary kinetic considerations, the shrinkage of (Cu,Ni)3Sn as well as other related observations in the reaction zone were investigated. Finally, the interfacial reactions of near-eutectic Sn–Ag–Cu solder with Ni(P)/Au metal finishes were studied theoretically and experimentally.