Observations of nucleation catalysis effects during solidification of SnAgCuX solder joints
|Title||Observations of nucleation catalysis effects during solidification of SnAgCuX solder joints|
|Publication Type||Journal Article|
|Year of Publication||2007|
|Authors||Anderson IE, Walleser J, Harringa JL|
|Type of Article||Article|
|Keywords||AG3SN 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.