The effects of flux on the wetting characteristics of near-eutectic Sn-Zn-In solder on Cu substrate

The effects of flux on the wetting characteristics of the near-eutectic Sn- Zn-tn solder alloy [composition: 86Sn-9Zn-51n] on Cu substrate have been st udied by using dimethylammonium chloride (DMAHCl), stearic acid (SA), lacti c acid (LA) and oleic acid (OA) as fluxes. Wetting time and maximum force w ere estimated from the wetting experiments. According to the wetting curves obtained by wetting balance apparatus, the SA and OA are not suitable as f lux for the near-eutectic Sn-Zn-ln solder on Cu substrate. However, the LA and DMAHCl provide a good wetting behavior. The lowest wetting time (0.27 s ) was obtained with 3.5 wt% DMAHCl as flux as-dipped at 300 degrees C. When the dipping temperature increased from 250 to 300 degrees C, the wetting t ime decreased obviously from about 0.6 to 0.4 s while the LA and DMAHCl wer e used as flux. When the content of LA was less than 5.0 vol% at 250 degree s C and 2.5 vol% at 300 degrees C, non-wetting or partial wetting was obser ved as determined by wetting curves. In addition, for the content of DMAHCl less than 1.5 wt% at 250 and 300 degrees C, non-wetting or partial wetting was also observed. Quite different from the most tin-based solders for Cu substrate, intermetallic compound gamma-Cu5Zn8 was found by the X-ray diffr action (XRD) and selected area electron diffraction (SAED) analyses at the interface of solder and substrate after etching out the unreacted solder la yer. The Zn element was enriched at the interface between solder and Cu sub strate as analyzed by line scanning. (C) 2000 Kluwer Academic Publishers.