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 Cu ₆(Sn, In)₅, Au-In-Sn and Au-In-Sn precipitates embedded in the Sn-rich matrix. © 2004 Elsevier B.V. All rights reserved.