Interfacial reaction and microstructural evolution for electroplated Ni and electroless Ni in the under bump metallurgy with 42Sn58Bi solder during annealing

Interfacial Reaction Between Molten Sn-Bi Based Solders and Electroless Ni-P Coatings for Liquid Solder Interconnects

“…The interfacial reaction products are in agreement with those reported for reactions of liquid Sn-37Pb, Sn-3.5Ag and also Sn-58Bi solders with similar electroless Ni-P substrates for reaction times from 5 s to 5 h [12], [15], [22]. In the present work where the samples were prepared using the Ni-P pads on commercial PCB boards and stored at high-temperature for longer reaction times, the interfaces between the IMC and the solder are wavier, and the pores in the Ni P layers are significantly larger than the previously reported Kirkendall voids [15].…”

“…They may involve multiple simultaneous processes, such as phase nucleation, lattice and/or grain boundary diffusion in the intermetallics, grain boundary grooving, grain coarsening, grain faceting, grain coalescing, and creation and/or annihilation of point defects [11]. There have also been studies of IMC formation between molten solders, such as Sn-Ag-Cu, Sn-Pb, Sn-Ag, Sn-Sb, Sn-Zn, Sn-Bi and pure Sn, and contact metallizations containing Ni-P or Cu [12]- [15]. In a few cases, the reaction times investigated extended to several hours, however, the majority of studies were short term, lasting from several seconds to under 1 h. Although IMC formation in the molten Sn-Bi/Cu and molten Sn-Bi/Ni-P systems is expected to be high from the results of these short term studies, it is important to explore the long term behavior of these systems so that the mechanism for IMC formation may be better understood, and modified to acceptable levels for molten solder interconnects.…”

Interactions between liquid Sn-Bi based solders and contact metals for high temperature applications

“…No Au IMC was detected at the interfaces, and hence it is believed that the Au layer dissolved into the solder completely during the reflow process. Identified using EDX analysis, the interfacial reaction products are in agreement with what were reported for reactions of liquid Sn-Pb, Sn-Ag and also Sn-Bi solders with similar electroless Ni(P) substrates [6,9,10]. The IMC that forms is Ni 3 Sn 4 .…”

“…[6,9,10], in the present study for longer reaction times, the interfaces between the IMC and the solder are relatively wavier. The IMC grains are larger and more heterogeneous, while their facets are more clearly developed (Figure 1b).…”

“…The IMCs formed during the soldering process also play an important role in the wettability of solders. Thus there are some studies of the IMC formation between the molten solders, including An-Ag-Cu, Sn-Pb, SnAg, Sn-Sb, Sn-Zn, Sn-Bi and pure Sn, and the various contact metallizations containing Ni(P) or Cu [6][7][8][9]. In a few cases, the reaction times were up to several hours.…”