SIZE-DEPENDENT DEWETTING AND SIDE-BAND REACTION OF EUTECTIC SNPB ON AU CU/CR MULTILAYERED THIN-FILM/

Dewetting of eutectic SnPb on blank Au(500 Angstrom)/Cu(1 mu m)/Cr(800 Angstrom) layered structure was found to have a solder size dependenc e. At 250 degrees C, if the solder weight fell below 4 mg, dewetting o ccurred from the center of the solder cap; if the solder weight went b eyond 6 mg, dewetting happened from the cap edge. In the latter case, a smaller cap with a higher wetting angle was formed a; the center and a ring of solder was left around the edge. Large voids were left in t he solder cap after dewetting in both cases. In contrast, all solder c aps were found to dewet from the edge on a patterned film at 250 degre es C if the solder ball was large enough to wet the whole film initial ly, irrespective of the solder size. For comparison, pure Sn, eutectic SnAg, and eutectic SnBi caps also dewetted from the edge of the Au/Cu /Cr thin film, irrespective of the solder size or whether the substrat e was patterned. Since eutectic SnPb on blank Au/Cu/Cr is the only cas e in which a large sideband growth was found and the dewetting occurre d from the center, we postulated sideband to be the main factor which controls the unusual dewetting. The link between them is discussed.