Effect of Cu content on IMC between Sn-Cu solder and Cu and Ni substrates

The reactions between Sn-xCu(x = 0, 0.1%, 0.3%, 0.7%, 0.9%, 1.5%) and Cu or Ni at 260, 280 and 290°C were studied to reveal the effect of varying Cu content on the composition and morphologies of intermetallic compounds (IMC) formed at the interface between solders and the substrate. The IMCs formed at the interface of Sn-Cu/Cu are Cu₆Sn₅. The higher the temperature is, the thicker the IMC layer forms. While soldering at the same temperature, with the increase of Cu content the thickness of IMC reduces first then increases. The thickness of IMC increases with the increase of Cu content when soldered with Ni at 260°C. And at the same time, the composition and morphologies of the IMC have notable changes. When the Cu content is below 0.3% (mass fraction), a continuous (Cu_xNi_1-x)₃Sn₄ IMC layer formed at the interface. When the Cu content is 0.7%, bigger facet (Cu, Ni_1-x)₆Sn₅ IMCs are found on the (Cu_xNi_1-x)₃Sn₄ IMC layer. At higher Cu content (0.9%-1.5%), stick shaped (Cu_xNi_1-x)₆Sn₅ IMCs are detected and (Cu_xNi_1-x)₃Sn₄ IMCs disappear. The effect of Cu content on the growth of IMC layer is analyzed and the formation and growth mechanisms of (Cu_xNi_1-x)₆Sn₅ IMC are discussed further.