In this study, interfacial reactions of electroless Ni(P) metallization of the ball-grid-array (BGA) substrate with the Sn-4 Ag-0.5 Cu (SAC405), Sn-3 Ag-0.5 Cu (SAC305) and Sn-9 In-3.5 Ag-0.5 Cu (SIAC) (wt.%) solder alloy were investigated, focusing on identification of the intermetallic compound (IMC) phases, the IMC growth rates and the consumption rate of the metallization layer at various liquid and solid state heat treatment conditions, e.g. extended reflow and solid state aging. A fixed volume of BGA solder ball (760 pm diameter) was used on a substrate metallization pad with a diameter of 650 mu m. The consumption of the electroless Ni(P) in SIAC solder was also lower than in the SAC solders. The presence of indium in the solder played a major role in inhibiting the consumption of Ni(P) in the soldering reaction. The stable IMCs initially formed at the interface of the Ni(P)/In-containing solder system was the (Cu, Ni)(6) (Sri, In)(5) phase. During further reflow, the (Cu, Ni)(3) (Sn, In)(4) IMC started forming because of the limited Cu content in the solder. Bulk of the SIAC solder also contained Cu-6(Sn, In)(5) and Ag-In-Sn precipitates embedded in the Sn-rich matrix. It was also found that more Ag-containing SAC405 solder shows higher Ni(P) consumption than SAC305 solder at the same heat treatment condition. (c) 2005 Elsevier B.V All rights reserved.