Intermetallic compound growth in lead free solder joints on Ag-based thick film coductors

In light of the RoHS-directive, that came into effect on July 1st 2006, lead free solders gained immensely in importance. The growth of the interfacial intermetallic compound layer between lead free solders and thick film metalizations was studied. A SnAg3.0Cu0.5-, a SnAg3.0Cu0.5Ni0.06Ge0.01- and a reactive-solder (SnCu1 + SnAg3.5 + Pd2) were tested on Ag-, Ag/Pd- and Ag/Pt-conductors. Samples were aged thermally for up to 1000 h at 150 degC and up to 168 h at 175 degC. It is shown that the growth of the intemetallic compound layer is much more dependent on the choice of metalization than on the chosen solder. Furthermore a model of the temperature-dependence of the diffusional constant for the combinations studied is presented.