Journal of SMT Article


Author: Gregory Henshall et al.
Company: Hewlett-Packard Co.
Date Published: 10/1/2002   Volume: 15-4

Abstract: The transition to Pb-free electronics has prompted the development of Pb-free component terminal finishes. Among the candidates being investigated are pure tin and dilute alloys of tin with either bismuth or copper. Of course, reliability of the solder joints made between the Pb-free SnAgCu alloy and these component terminal finishes is essential. Metallurgical incompatibility between the SnAgCu solder alloy and the terminal finishes could result in solder joint brittleness, low strength or lack of thermal fatigue resistance, particularly following aging of the joint (e.g. over the life of a product in the field).

In this study, we investigated the reliability of SMT solder joints made with Sn/3.8Ag/0.7Cu solder and leaded components with a variety of surface finishes: pure Sn, Sn3Cu, and Sn alloyed with Bi in concentrations of 1, 3 and 6 weight percent. This investigation included metallographic examination and lead pull testing of aged and unaged joints. Accelerated thermal cycling of surface mount joints also has been initiated and preliminary results are described. The results of a limited study on the quality of wave soldered, through-hole joints with SnBi and SnPb platings are also presented. Our findings suggest that all of the Pb-free terminal finishes investigated produce joints with SnAgCu solder that perform at least as well as conventional, fully SnPb joints.

Key words: Pb-free solder, terminal finish, reliability.

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