Evaluation of Lead- Free Solder Joints in Electronic Assemblies |
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Authors: | I Artaki A M Jackson P T Vianco |
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Affiliation: | (1) AT&T Bell Laboratories, 08542-0900 Princeton, NJ;(2) Sandia National Laboratories, 87185 Albuquerque, NM |
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Abstract: | The feasibility of printed circuit board assembly with lead-free solder alloys was investigated. Studies were conducted with
two baseline eutectic binary alloys, SnBi and SnAg, and three new lead-free solder formulations: (1) 91.8Sn-4.8Bi-3.4Ag (wt%)
developed at Sandia Laboratories, (2) 77.2Sn-20In-2.8Ag developed at Indium Corp. of America, and (3) 96.2Sn-2.5Ag-0.8Cu-0.5Sb
provided by AIM Inc. The basic physical properties (melting temperature, wetting, mechanical strength) pertinent to each of
the newly developed alloys are described. The feasibility of 0.4 mm pitch assembly was established with each of the lead-free
solder alloys investigated, although the processing windows were generally found to be narrower. All solder joints exhibited
good fillets, in accordance with the workmanship standards. Wetting of the lead-free solders was significantly improved on
immersion tin vs imidazole finished circuit boards. The laminates did not suffer thermal degradation effects, such as warpage,
delamination, or severe discoloration (reflow was performed under an inert atmosphere). It is thus concluded that the manufacturability
performance of the new solder formulations is adequate for surface mount applications. |
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Keywords: | Electronic assembly lead-free solder solderability |
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