Interfacial reactions on electrolytic Ni and electroless Ni(P) metallization with Sn–In–Ag–Cu solder

Abstract

In this study, interfacial reactions of electrolytic Ni and electroless Ni(P) metallization of the ball-grid-array (BGA) substrate with the molten Sn–9In–3.5Ag–0.5Cu (wt.%) solder alloy were investigated, focusing on identification of the intermetallic compound (IMC) phases and the IMC growth rates at various reflowing times. A fixed volume of BGA solder ball (760 μm diameter) was used on a substrate metallization pad with a diameter of 650 μm. The peak reflow temperature was fixed at 240 °C while the reflow time was varied between 1 and 120 min. The intermetallic compounds thickness was lower on the electroless Ni(P)/solder interface. The consumption of the electroless Ni(P) in Sn–9In–3.5Ag–0.5Cu was also lower than that of the electrolytic Ni. The appearance of a P-rich Ni layer at the interface played a major role in inhibiting the overall interfacial reaction in the soldering reaction with the electroless Ni(P) metallization. The stable IMC initially formed at the interface was the (Cu, Ni) 6 (Sn, In) 5 phase. During further reflowing, the (Cu, Ni) 3 (Sn, In) 4 IMC started forming because of the limited Cu content in the solder. These bright low-Cu IMCs appeared earlier at the interface of the Ni/solder system than the Ni(P)/solder system. Bulk of the Sn–9In–3.5Ag–0.5Cu solder contained Cu 6(Sn, In) 5, Au–In–Sn and Au–In–Sn precipitates embedded in the Sn-rich matrix.