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

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 Cu6(Sn, In)5, Au-In-Sn and Au-In-Sn precipitates embedded in the Sn-rich matrix.