Oxygen-Free Compound Casting of Aluminum and Copper in a Silane-Doped Inert Gas Atmosphere: A New Approach to Increase Thermal Conductivity

Abstract

Novel aluminum-copper compound castings devoid of oxide layers at the interface between the joining partners were developed in order to increase the thermal conductivity of the hybrid component. Due to the natural oxide layers of both aluminum and copper, metallurgical bonds between such bi-metal castings cannot be easily achieved in conventional processes. However, in an atmosphere comparable to extreme high vacuum created by using silane-doped inert gas, metallurgical bonds between the active surfaces of both aluminum and copper can be realized without additional coatings or fluxes. An intermetallic was created between aluminum and copper. Thus, very high thermal conductivities could be obtained for these hybrid castings, exceeding those of conventionally joined samples considerably. The intermetallic phase seams emerging between the joining partners were investigated using scanning electron microscopy and X-ray diffraction. The reduction of casting temperatures resulted in narrower intermetallic phase seams and these in turn in a much lower contact resistance between the two joining partners. This effect can be utilized for increasing the heat transfer capabilities of compound casting components employed for cooling heat sources such as high-power light-emitting diodes.

Oxygen‐Free Production—From Vision to Application

“…Figure 11. Comparison of the data obtained by Fromm et al[62] (orange and blue) in comparison to literature results from ref [79,80]…”

“…Oxide layers of the involved metals generally hinder the diffusion process for the formation of a metallurgical bond in compound casting, which is why direct compound casting without further measures is usually not successful with the material combination aluminum-copper. [62] Fromm et al investigated the effect of transferring the compound casting process of aluminum on copper into an oxygen-free atmosphere. For this, a gravity-casting set-up was placed inside a glove box filled with the oxygen-free atmosphere described in chapter 2.1.…”

“…[62] Copyright 2022, The Authors, published by Springer. [62] (orange and blue) in comparison to literature results from ref. [79,80].…”

“…Obviously, the mold temperature had a much stronger influence on the compound zone thickness than the crucible temperature which was attributed to the high thermal conductivity of copper. [ 62 ] Generally, it is possible to control the compound zone thickness over a wide range by carefully adjusting the process temperatures.…”

“…Compound casting leads to much higher values than mechanical connections with thermal paste and can reach values of state of the art processes like soldering or compound casting with intermediate layers. [ 62 ] Compared to soldering, compound casting is capable to join much larger surfaces. Hence, new products with high interfacial thermal conductivity might be possible.…”