The effect of Ag, Fe, Au and Ni on the interfacial reactions between Sn-based solder and Cu substrate has been investigated in this paper. Based on the solubility of the alloying elements in the Sn-Cu intermetallic compound (IMC) layers these elements can be divided into two categories: (i) alloying elements that do not dissolve significantly in either Cu6Sn5 or Cu3Sn and (ii) elements that exhibit significant solubility in Cu6Sn5 and also to Cu3Sn. It is shown that the latter group of elements have stronger effect on the growth behaviour of IMC's in the Sn-Cu system than those belonging to the first group. Of the investigated elements Ni had the most prominent effect on the growth kinetics. It reduced greatly the thickness of Cu3Sn and consequently also the total IMC layer thickness. Au had similar but markedly weaker effect. On the contrary, Fe and Ag only slightly decreased the total IMC layer thickness, and more importantly did not change the thickness ratio of Cu6Sn5 to Cu3Sn in comparison to the pure Sn-Cu system.
- Intermetallic compounds
- Lead-free solders