Interfacial reactions between Ga and Cu-xNi (x=0, 2, 6, 10, 14) substrates and the strength of Cu-xNi/Ga/Cu-xNi joints

In Situ Observation of the Ga- and Cu-Based Substrate Reaction by Synchrotron Microradiography

“…However, the nucleation and growth of the CuGa 2 is slow compared with the Ga/Cu6Ni reaction, and it takes more time for the IMCs formed during the cooling period to reach a final stable state which is at around 78 °C meaning the rate of Cu diffusing into the Ga is slow. Therefore, the Ni addition in the substrate accelerates the growth of IMCs both during the heating and cooling stage …”

“…The recorded temperature profiles in real time are shown in Figure . Previous work has shown that the IMC growth rate between Ga- and Cu-based substrates is sluggish at room temperature and it takes over 7 days to form a joint . Elevated temperature can accelerate the growth of the IMCs to meet industrial demands and allow in situ observations to be carried out over relatively short timeframes to investigate the formation of IMCs.…”

“…Figure shows the procedure for the ex situ experiments. Cu6Ni substrates were used due to the faster IMC growth rate compared to Cu substrates and it was used to compare the growth of IMCs with in situ experiments. , All of the substrates were immersed in 5% HCl to remove the oxidation, and 5% HCl was used as flux as well for the soldering process. Prepared Ga discs were put on a 5 mm × 25 mm Cu6Ni coupon (approximately 1 mm thick) as shown in Figure a.…”

“…Previous studies have shown that similar to Cu6Ni, Cu-25 atom %Ni can also accelerate the growth of intermetallics and a previous study showed this is likely to be replicated in the Ga/Cu−Ni system. 21,25 First, the lattice parameters of a Cu unit cell (Figure 4a) and a Cu-25 atom %Ni unit cell (Figure 4b), both with a starting lattice parameter a of 3.6035 Å (PDF number 00-004-0836) were optimized. To simulate the surface of Cu and Cu-25 atom %Ni, slabs with 15 Å vacuumed space were created by cleaving the (111) face of the corresponding optimized bulk structures (Figure 4d,e).…”

“…17,21−23 It has been found that Ni-containing substrates accelerate the formation of IMC layers at room temperature and the growth rate of Ga intermetallics when reacting with Cu6Ni substrates is fast compared with other Cu−Ni substrates, and a similar phenomenon has been observed during Sn and Cu−Ni reactions. 21,23 When Ga reacts with Cu substrates, a thin IMC layer of Cu 9 Ga 4 forms close to the substrate, and a significantly thicker layer of CuGa 2 forms above this layer. 23 However, when Ni is present in the substrate, the IMC layer becomes more complex, a nanocrystalline IMC layer of Ga 5 Ni and CuGa 2 forms close to the substrate, and a large layer of CuGa 2 forms further away.…”