Interfacial Reactions between Ga and Cu-10Ni Substrate at Low Temperature

Abstract

Ga alloys have been attracting significant renewed attention for lowtemperature bonding applications in electronic packaging. This study systematically investigates the interfacial reaction between liquid Ga and Cu-10Ni substrates at 30 °C. In addition to CuGa 2 formed from binary Ga/Cu couples, a layer of nanocrystalline Ga 5 Ni and CuGa 2 formed between the Cu-10Ni substrate and the blocklike micrometer scale CuGa 2 layer. The growth of interfacial intermetallics (IMCs) on the Cu-10Ni substrate was substantially accelerated compared to the IMC growth in binary Ga/Cu couples. Reaction kinetics study shows the IMC growth from the Cu-10Ni substrate was controlled by reaction and volume diffusion, while the IMC growth from the Cu substrate was controlled by volume diffusion. It is also found that the presence of Ni within the CuGa 2 phase resulted in improved thermal stability and a smaller coefficient of thermal expansion during heating from 25 to 300 °C, using synchrotron XRD analysis. There was least thermal expansion anisotropy among most of the IMCs that form in conventional Sn-based solder alloys, including Cu 6 Sn 5 and so forth. It is concluded that using a Cu-10Ni substrate as opposed to a Cu substrate could achieve sufficient metallurgical bonding within shorter processing time. The results have implications for broadening the application temperatures when using Ga as a low-temperature joining material.

Low Temperature Cu/Ga Solid–Liquid Inter-Diffusion Bonding Used for Interfacial Heat Transfer in High-Power Devices

“…From Figure 5d, a thin layer of dark phase can be seen at the copper wire/θ-CuGa 2 layer interface, and it may be γ 3 -Cu 9 Ga 4 phase based on the EDS results and Cu-Ga phase diagram [23,24]. This is consistent with the research that a thin layer of γ 3 -Cu 9 Ga 4 is formed at the Cu/CuGa 2 interface [25,26]. Ancharov's research shows that [27,28] the only interaction product of copper with gallium is the CuGa 2 at temperatures near 20 • C for more than two days, and there are no other copper-gallium intermetallic compounds.…”

Gallium-Enhanced Aluminum and Copper Electromigration Performance for Flexible Electronics

“…56 In a similar study, where the Ga/Cu system was allowed to react for a long time, above approximately 260 °C, a very thin Cu 9 Ga 4 intermetallic was also found, which was formed by the decomposition of CuGa 2 . 57,58 In consonance with the binary phase diagram, in the case of the Al−Ga system, upon heating and subsequent cooling, because no intermetallic phases form, the most probable outcome is phase/material segregation. In the case of the binary Cu−Ga system, upon Joule heating, it can be expected that intermetallic phases form.…”

“…With additional heating up to 200 °C, the formed CuGa 2 intermetallic was found to be very stable, and its properties (lower hardness and Young’s modulus as compared to Cu–Sn alloys) make it extremely attractive for interconnects . In a similar study, where the Ga/Cu system was allowed to react for a long time, above approximately 260 °C, a very thin Cu 9 Ga 4 intermetallic was also found, which was formed by the decomposition of CuGa 2 . , …”

Recent Development of Liquid Metal‐Based Functional Materials Combined with Common Transition Metals

“…[ 55 ] The intermetallic compound CuGa 2 can quick form between gallium and copper. [ 51,90 ] In the Cui et al. study, [ 28 ] a shallow trace was left after put a LM droplet onto Cu substrate at 100 °C for 2 h. As shown in Figure a, traces deepened at 200 °C and LMs adhered to the copper substrate, the surface of LMs metallic became dull at this time.…”