Lead-free soldering: Materials science and solder joint reliability

Abstract

Since the National Electronics Manufac tu r ing Initiative recommended Sn3.9Ag-0.6Cu for refl ow soldering and Sn-3.5Ag and Sn-0.7Cu for wave soldering in 2000, great effort has been made to address the reliability issues of lead-free soldered packages. Investigation of the dependence of properties of bulk solder alloys on compositions and processes can, of course, greatly help reliability engineering of solder joints. However, because of the strong effect of the interface between solder and soldered metal on the reliability of fi ne pitch solder joints, research of bulk solders is not enough to answer all the questions. The infl uences of composition and microstructure of solder joints on the reliability of bond interface should also be studied. In this issue, fi ve papers address materials issues directly related to solder joint reliability. In the fi rst paper, I. Dutta et al. summarize their research in characterization of microstructural coarsening in Sn-Ag based solders and its effects on mechanical properties of bulk solder as well as reliability of solder joints. In the eutectic SnAgCu alloy, the volume fraction of Cu 6 Sn 5 is much smaller than that of Ag 3 Sn and Cu 6 Sn 5 coarsens more rapidly than Ag 3 Sn. Therefore, Ag 3 Sn is the major contributor to the effects of coarsening on mechanical properties of SnAgCu solders and reliability of joints. The data indicate that a lower rate of interfacial failure of solder joints can be expected if electronic devices are handled with greater caution in the fi rst several days after assembly. The second paper by F. Guo et al. is Lead-free Soldering: Materials Science and Solder Joint Reliability