Formation of Intermetallic Compounds Between Liquid Sn and Various CuNi x Metallizations

Abstract

Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the subsequent phase transformations during the cooling were investigated with an emphasis on the microstructures of the reaction zones. It was found that the extent of the microstructurally complex reaction layer (during reflow at 240°C) does not depend linearly on the Ni content of the alloy metallization. On the contrary, when Cu is alloyed with Ni, the rate of thickness change of the total reaction layer first increases and reaches a maximum at a composition of about 10 at.% Ni. The reaction layer is composed of a relatively uniform continuous (Cu,Ni) 6 Sn 5 reaction layer (a uniphase layer) next to the NiCu metallizations and is followed by the two-phase solidification structures between the single-phase layer and Sn matrix. The thickness of the two-phase layer, where the intermetallic tubes and fibers have grown from the continuous interfacial (Cu,Ni) 6 Sn 5 layer, varies with the Ni-to-Cu ratio of the alloy metallization. In order to explain the formation mechanism of the reaction layers and their observed kinetics, the phase equilibria in the Sn-rich side of the SnCuNi system at 240°C were evaluated thermodynamically utilizing the available data, and the results of the Sn/Cu x Ni 1-x diffusion couple experiments. With the help of the assessed data, one can also evaluate the minimum Cu content of Sn-(Ag)-Cu solder, at which (Ni,Cu) 3 Sn 4 transforms into (Cu,Ni) 6 Sn 5 , as a function of temperature and the composition of the liquid solders.

Intermetallic Formation and Fluidity in Sn-Rich Sn-Cu-Ni Alloys

“…For example, the liquidus projections of the Sn-rich corner by Lin et al, 17 Snugovsky et al, 16 and Vuorinen et al 2 are fundamentally different, as shown in Fig. 1 6 Sn 5 -type compound and instead report that (Cu,Ni) 6 Sn 5 can contain a Ni content throughout the range from 0 at.% to approximately 25 at.%.…”

“…Due to this relevance to soldering, a range of solder joint studies have been conducted using the Sn-Cu-Ni system where the Cu and Ni are initially present either in the solder alloy or in the substrate. [1][2][3][4][5][6][7][8] It is now clear that, when soldering in this system, the intermetallic(s) in the reaction layer of the joint exhibit significant mutual solubility of Cu and Ni, which influences both the growth kinetics of the reaction zone and the type of intermetallic compounds (IMCs) that form. 9 Recently, Ni has also been shown to stabilize the hightemperature hexagonal allotrope of (Cu,Ni) 6 Sn 5 at room temperature.…”

Nucleation and Growth of Tin in Pb-Free Solder Joints

“…Sn-0.7Cu-0.05Ni has been used since 1999 in applications that benefit from its higher 'Ragone fluidity' [24,25], stabilised hexagonal (Cu,Ni)6Sn5 [26], higher compliance [27] and higher impact strength [28] compared with high-silver SAC solders. The 0.05wt%Ni addition is significant with respect to the Sn-Cu-Ni phase diagram [29,30] and produces a slightly hypereutectic composition [31] which leads to reduced Cu substrate dissolution [27,32,33], dopes the Cu6Sn5 with Ni [26,31] and significantly alters the solidification sequence [3] compared with Sn-0.7Cu.…”

Effects of Reflow Time on the Interfacial Microstructure and Shear Behavior of the SAC/FeNi-Cu Joint

“…In Figure 4b, for example, the element Ni from UBM diffused into the solder rather than producing Ni-Sn IMC phase near the interface. The EDS result in Table 1 showed that some of the Cu 6 Sn 5 phase within solder near the interface turned out to be Cu 6 Sn 5 containing Ni, i.e., (Cu,Ni) 6 Sn 5 , where some places of Cu atoms in Cu 6 Sn 5 crystalline lattice were occupied by the Ni atoms [20]. Figure 4e and the possible phases.…”