Journal of SMT Article


Authors: Gregory Henshall, Ph.D., Robert Healy, Ranjit S. P
Company: Hewlett-Packard Co., Cookson Electronics, Nihon Su
Date Published: 10/30/2008   Volume: 21-4

Abstract: Recently, the industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic Sn-Ag-Cu (SAC) alloys. New wave solder alloys have been developed with the intent of addressing concerns with copper dissolution, barrel fill, wave solder defects, and the high cost of alloys containing significant amounts of silver. Concerns regarding the poor drop/shock performance of near-eutectic SAC alloys led to the development of low Ag alloys to improve the mechanical strength of BGA and CSP solder joints. Most recently, investigations into new solder paste alloys for mass reflow have begun. The full impact of these materials on printed circuit assembly (PCA) reliability has yet to be determined.

The increasing number of Pb-free alloys provides opportunities to address the important issues described above. At the same time, the increase in choice of alloys presents challenges in managing the supply chain and introduces a variety of risks, particularly to the reliability of PCAs.

This paper provides the results of an iNEMI study of the present state of industry knowledge on Sn-Ag-Cu alloy “alternatives,” including an assessment of existing knowledge and critical gaps. Focus areas are recommended for closing these gaps, with the additional goal of avoiding repeated investigations into issues already resolved. Finally, efforts to update industry standards to account for the new alloys and to better manage supply chain complexity and risk are described.

Key words: Lead-free alloys, alternative alloys, low silver alloys, microalloying, reliability

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