SOLDERING REACTION BETWEEN EUTECTIC SNPB AND PLATED PD NI THIN-FILMS ON CU LEADFRAME/

In the soldering reaction at 200 degrees C between eutectic SnPb and p lated Pd/Ni on Cu leadframes, two thicknesses of Pd of 760 and 2500 An gstrom were used. Even very thin Pd can lead to continuous spreading o f the solder on the leadframe; no stable wetting angle can be observed . Anisotropic spreading and spike formation were found due to the mech anical effect ofrolling of the leadframe, and they are more pronounced in the thinner Pd samples. In the interfacial reaction, we have obser ved the formation of a ternary Pd-Ni-Sn compound and Ni3Sn4. While spa lling of the ternary compound occurs, no spalling of the Ni3Sn4 was fo und. The latter forms a rather uniform layer consisting of small scall op-type grains. We found that the growth rate of Ni3Sn4 is much slower , by a factor of about 10, than that of Cu6Sn5 in the reaction between Cu and eurectic SnPb. (C) 1997 American Institufe of Physics.