It was found that whiskers grow from solder joint fillets, where the thickness is less than 25 µm, unless REE was present. Detailed metallurgical analysis on components before assembly and on solder joints before and after testing was performed. Whisker length, diameter, and density were measured. After assembly, all the boards were cleaned, and half of them were recontaminated (1.56 µg/cm 2 Cl −). Cleaned and contaminated small outline transistors, large leaded quad flat packs (QFP), plastic leaded chip carrier packages, and solder balls with and without rare earth elements (REE) were soldered to custom designed test boards with Sn3Ag0.5Cu (SAC305) solder.
This article describes the results of a whisker formation study on SAC305 assemblies, evaluating the effects of lead-frame materials and cleanliness in different environments: low-stress simulated power cycling (50–85☌ thermal cycling), thermal shock (–55☌ to 85☌), and high temperature/high humidity (85☌/85% RH).
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