The proposed invention uses inoculants to minimize, or eliminate, solidification undercooling of Sn and Sn-based solders in order to refine the microstructure and improve the mechanical properties of the solder joints. The basic concept is to add a fine powder of an appropriate intermetallic compound, or compounds, to the solder alloy in order to provide well dispersed inoculants into the solder that will act as nucleation sites to reduce undercooling during solidification. In addition, by selecting compounds that are not completely dissolved in liquid solder, a fine dispersion of particulates remain in the solder joint to provide resistance to creep that is important for solders being used at elevated temperatures. The essential characteristics of the powder additions are that they must have an appropriate crystal structure to act as a potent catalyst for Beta-Sn nucleation from the liquid Sn-based solder alloy, they must have a higher melting temperature than the liquid solder so that they remains solid during the soldering process, they must have a low solubility in liquid solder so that it doesn’t dissolve during soldering, they must not impart poor mechanical properties to the joint, and they should be reasonably inexpensive and easy to manufacture into powder form or otherwise incorporate into solder alloys.
Inventors
Eliot D Specht Materials Science and Technology Div
Contact
To learn more about this technology, email [email protected] or call 865-574-1051.