Observations of nucleation catalysis effects during solidification of SnAgCuX solder joints

TitleObservations of nucleation catalysis effects during solidification of SnAgCuX solder joints
Publication TypeJournal Article
Year of Publication2007
AuthorsAnderson IE, Walleser J, Harringa JL
Journal TitleJom
Date PublishedJul
Type of ArticleArticle
ISBN Number1047-4838
Accession NumberISI:000247895300007
KeywordsAG3SN PLATE FORMATION, alloys, microstructure, SN-AG-CU

While modification of a strong (high Cu) Sn-Ag-Cu (SAC) solder alloy with a substitutional alloy addition (X= Co, Fe, Zn, and Ni) for Cu has been demonstrated to enhance solder joint strength and ductility after aging at 150 degrees C for 1,000 h, control of the as-solidified SAC+X solder joint microstructure is also needed to inhibit undercooling and nucleation of brittle pro-eutectic phases (e.g., A 93 Sn). Bulk undercooling measurements of SAC+X alloys and microstructural analysis of SAC+X solder joints were used to rank the effectiveness and consistency of low-level (X < 0.15 wt.%) substitutional additions to a base SAC composition, Sn-3.5Ag-0.95Cu (wt.%). This SAC composition was selected to favor thermodynamically the nucleation of pro-eutectic Cu 6 Sn 5 over that of Ag3Sn and the formation of an enhanced ternary eutectic fraction in the joint microstructure, while retaining a pasty range that is only 3 degrees C. Using differential scanning calorimetry with sample pans that serve as either inert (aluminum) or actively wetting (copper) substrates, reflow cycles were studied that simulated surface mount (1.5 degrees C/s) and ball-grid array (0.17 degrees CA) cooling rates. Of the SAC+X solders tested with copper pans, X = Zn appeared to be most effective and consistent, providing catalytic enhancement of the nucleation temperature for even the minimum concentration (0.05 wt.%) and lowest cooling rate.

Alternate JournalJom