Soldering reaction between eutectic SnPb and plated Pd/Ni thin films on Cu leadframe

Abstract

In the soldering reaction at 200 °C between eutectic SnPb and plated Pd/Ni on Cu leadframes, two thicknesses of Pd of 760 and 2500 Å were used. Even very thin Pd can lead to continuous spreading of the solder on the leadframe; no stable wetting angle can be observed. Anisotropic spreading and spike formation were found due to the mechanical effect of rolling of the leadframe, and they are more pronounced in the thinner Pd samples. In the interfacial reaction, we have observed the formation of a ternary Pd–Ni–Sn compound and Ni3Sn4. While spalling of the ternary compound occurs, no spalling of the Ni3Sn4 was found. The latter forms a rather uniform layer consisting of small scallop-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 eutectic SnPb.