Microstructural stability, solders

Aging studies are conducted as an indicator of long-term microstructural stability under field conditions, i.e., how the microstructure evolves with time and temperature. The IMC AgsSn that is dispersed throughout the bulk solder coarsens, whereas the dendritic Cu3Sn IMC in the bulk solder was observed to decrease. A layer of CusSn (e-phase) forms nearest to the copper [33]. 

Ohnuma, I. Migashita, M. Anzai, K. Liu, X.J. Ohtani, H. Kainuma, R. Ishida, K. Alloying effects in near-eutectic Sn-Ag-Cu solder alloys for improved microstructural stability. J. Electron. Mater. 

The 150 °C (302 °F) 24 h anneaUng treatment was more effective at stabilizing the solder microstructure over the entire test temperature regime. A relatively good correlation was obtained with a single sinh law equation for dddt, (Eq 23) ... 

Taking the foregoing concerns into account this chapter discusses in detail the key metallurgical aspects including as-solidified microstructure, thermal stability characteristics, effects of elemental additions, and thermal aging, etc. as they relate to the Sn-Ag, Sn-Cu and their ternary alloys (Sn Ag Cu) into account. These alloy systems are the subject of much attention as solder replacement candidates for solders of the Pb-Sn system, particularly eutectic Sn-Pb. In addition, the chapter discusses the major mechanical properties of interest for electronic packaging applications as a consequence of their metallurgical characteristics. 

Betrabet, H.S. McGee, S.M. McKinlay, J.K. Processing dispersion-strengthened Sn-Pb solders to achieve microstructural refinement and stability. Scr. Metall. Mater. 1991, 25, 2323-2328. 

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