Pb-free solders: Part 1. Wettability testing of Sn-Ag-Cu alloys with Bi additions

Maximum bubble pressure, dilatometric, and meniscographic methods were used in the investigations of the surface tension, density. wetting time, wetting force, contact angle, and interfacial tension of liquid alloys of Sn-Ag-Cu eutectic composition with various additions of Bi. Density and surface tension measurements were conducted in the temperature range 250-900 degrees C. Surface tensions at 250 degrees C measured under a protective atmosphere of Ar-H-2 were combined with data from meniscographic studies done under air or with a protective flux. The meniscographic data with a nonwetted teflon substrate provided data on interfacial tension (solder-flux), surface tension in air, and meniscographic data with a Cu substrate allowed determinations of wetting time, wetting force, and calculation of contact angle. The calculated wetting angles from meniscographic studies for binary Sn-Ag eutectic and two ternary Sn-Ag-Cu alloys were verified by separate measurements by the sessile drop method under a protective atmosphere with a Cu substrate. Additions of Bi to both ternary alloys improve the wettability and move the parameters somewhat closer to those of traditional Sn-Pb solders.