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Interface phenomena in lead-free soldering

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1 Author(s)
Suganuma, K. ; Inst. of Sci. & Ind. Res., Osaka Univ., Japan

There are many aspects of technological developments required for the establishment of lead-free microsoldering in the electronics industrial field. The structural integrity of solders and of soldered circuits is one of the great concerns. Most of Sn alloys involving pure Sn, Sn-Ag, Sn-Bi or their ternary alloys form two intermetallic compounds at the interfaces with Cu, i.e., Cu6Sn5 and Cu3Sn. The former reaction layer is much thicker than the latter and the integrity of interface is strongly influenced by the presence of the Cu6Sn5 layer. The Sn-Zn alloy forms different Cu-Zn intermetallic compounds without Sn at the interface with Cu. These reaction layers degrade the heat resistance of the Sn-Zn/Cu interface beyond 130°C. The coating of Ni/Pd/Au layers on Cu. however, can raise the resistance up to 150°C. In all Sn-Bi alloys except for the eutectic alloy, lift-off was frequently observed. Lift-off occurs even at 2 wt% Bi content, which is closely related to the segregation of Bi to the solder/Cu interface. Rapid cooling from soldering temperature can stop the lift-off quite effectively

Published in:

Environmentally Conscious Design and Inverse Manufacturing, 1999. Proceedings. EcoDesign '99: First International Symposium On

Date of Conference:

1-3 Feb 1999