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

Abstract

• This is a conference paper [ c IEEE]. It is also available at:http://ieeexplore.ieee.org/ Personal use of this material is permitted.However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE AbstractLiquid solder interconnects are promising as an alternative approach to conventional high melting point solder interconnects for applications where the operating temperature is likely to exceed 125°C. In order to ensure that a liquid solder interconnect remains in contact with the terminations on the component and the substrate, and that electrical contact between them remains unbroken, there must be some growth of an intermetallic compound (IMC) at the interfaces between the solder and the contact metallizations. However, given that IMC growth is generally much faster when the solder is liquid, the growing IMC must act as a strong diffusion barrier to suppress further IMC growth. This paper presents preliminary studies of liquid-phase Sn-Bi based solders that result in stable interfaces between the solders and three common contact metallizations, consisting of electroless Ni(P)/Au, of Cu and of Ti-W. Small quantities (1 or 2 %) of an additional element, including Cr, Si, Zn, Ag, Au, Al and Cu, have been alloyed with the eutectic Sn-Bi composition to find an effective inhibitor additive that can achieve a strong IMC diffusion barrier. IMCs and their growth rates, as well as the consumption rates of the three contact metallizations in contact with the molten solders, were investigated. Storage temperatures of 200°C and 240°C were used, with storage times ranging between two hours and one month. Results to date show that suitable additives can significantly reduce IMC growth rates for both the Ni(P)-Au and Cu contact metallizations, while no appreciable IMC growth is observed for Ti-W in contact with both the original and the various alloyed Sn-Bi based solders. Based on the current results, criteria to further assist the design of feasible molten liquid solder -contact metallization systems have been deduced.

Low Melting Temperature Sn-Bi Solder: Effect of Alloying and Nanoparticle Addition on the Microstructural, Thermal, Interfacial Bonding, and Mechanical Characteristics

“…However, due to their high surface energy, nanoparticles increase the probability of agglomeration with each other in the solder matrix. Such nonuniform dispersion and aggregation of nanoparticles degrades the reliability of the solder matrix [123][124][125][126], an optimal content evaluation for each nanoparticle should be made. Strengthening the effect by adding nanoparticles can be obtained by the following factors.…”

Properties and Microstructures of Sn-Bi-X Lead-Free Solders

“…Li et al [29] have done research on the effect of a small amount of Al addition on the wettability of the Sn-58Bi solder. Due to Al being too active or the flux being not matched to this solder, it was found that the wettability of the Sn-58Bi solder became poorer after adding 2 wt.% Al to the eutectic Sn-58Bi solder.…”

“…The IMC nucleation, growth, and its type are responsible for the solder reliability [83,84]. In addition, the IMC formed at first could function as a hard diffusion barrier to restrain further IMC growth [29]. At the same time, a part of Bi atoms dissolve into the Cu 6 Sn 5 intermetallic compound layer and then segregate at the Cu/Cu 3 Sn interface.…”

“…The addition of 1 wt.% Cu also had no effect on the IMC growth. Li et al [29] added 1.0 wt.% Au and Zn to the Sn-58Bi solder and found that the growth rate of the IMCs of the composite solders was increased. In contrast, addition of the 2 wt.% Cr, 2 wt.% Si, and 1 wt.% Ag elements reduced the growth rate and did not affect critically the interfacial microstructures at 200 ∘ C and 240 ∘ C for 120 h.…”

Electroless Ni-W-P Alloys as Barrier Coatings for Liquid Solder Interconnects

“…One way to slow down the liquid state interfacial reaction is by adding a special inhibitor additive into the solder alloy. However, it has been found that amongst a broad range of additional elements studied, some limited success has only been achieved with the addition of copper to the eutectic Sn-Bi solder [2], which is the most suitable low melting solder for liquid solder applications. Al has also been reported as a suitable inhibitor [1], but has only been tested successfully under vacuum conditions, and interferes with solder wetting in air.…”