MORPHOLOGY OF WETTING REACTION OF EUTECTIC SNPB SOLDER ON AU FOILS

We have studied the wetting behaviors of eutectic SnPb solder caps on pure Au foils at 200 degrees C. Surface morphology, wetting angle, and wetting tip stability were examined by scanning electron microscopy a nd energy dispersion x-ray analysis. In addition, interfacial reaction in the bulk diffusion couple of tile solder and Au was studied. Inter metallic compound (AuSn4) was observed on the surface of the solder ca p, often called the cold joint, as early as 2 a of reflow at 200 degre es C. The wetting angle decreased with reflow lime but remain ed const ant after 180 s of reflow. However, the Side-band width and the diamet er of the solder cap continuously increase with the reflow time to 5 m in when the entire eutectic SnPb solder cap is fully consumed by inter metallic compound formation. In the bulk diffusion couple of eutectic SnPb and Au, the growth and morphology of the intermetallic compound ( AuSn4) was influenced by hu dissolution. Since Au, showing excellent w etting behavior, forms the platelet-type intermetallic compound, we po stulate that the wetting rate may be improved with a system containing platelet-type intermetallic compound formation fbr the eutectic SnPb solder. (C) 1996 American Institute of Physics.