By DE Staff December 10, 2024
Contract manufacturers and design engineers in the aerospace, semiconductor, high-power electronics and energy industries have been turning to diffusion bonded metals to produce new cutting-edge innovations. aluminium construction
Diffusion bonding is an essential joining method used to achieve a high-purity interface when two similar or dissimilar metals require superior structural integrity but the traditional brazing approach fails to yield quality results. The process involves applying high temperature and pressure to metals mated together in a hot press, which causes the atoms on solid metallic surfaces to intersperse and bond.
Today, much of the innovation occurring in either high-demand or high-quality industrial sectors involves aluminum as one or more of the layers of metals that are bonded. Aluminum, and its broad family of alloys, is prized as a lightweight metal with strong structural integrity, high electrical and thermal conductivity, corrosion resistance and a malleability that makes it easy to shape.
Aluminum’s unique blend of lightness, strength and purity makes it indispensable across various industries. In aerospace, its high strength-to-weight ratio is crucial for structural components. For semiconductor equipment, aluminum enables the fabrication of intricate, contamination-free channels essential for gas and fluid flow, avoiding the impurities inherent in traditional joining methods like brazing or welding. Furthermore, aluminum’s compatibility with diffusion bonding allows for the creation of complex cooling channels in high-power electronics, injection molds, and specialized heat exchangers—designs often impossible to achieve through conventional machining.
Unfortunately, the characteristics of aluminum present a challenge for the traditional diffusion bonding process, which involves the application of radiant heat into the metal layers while in a vacuum furnace. Aluminum tends to reflect radiant heat and has a relatively low melting point in relation to the temperatures that must be achieved for proper diffusion bonding.
Engineers cleverly confronted the issue by developing a conductive heating method which more rapidly reaches bonding temperature. This new approach offers an alternative to traditional diffusion bonding by circumventing the slow process of radiant heating structural assemblies in a vacuum environment.
The c.BOND machine utilizes precisely controlled heat conduction, instead of radiation, to enable high speed production of aluminum-to-aluminum or aluminum-to-dissimilar-material parts. (Credit: PVA TePla)
The c.BOND machine utilizes precisely controlled heat conduction, instead of radiation, to enable high speed production of aluminum-to-aluminum or aluminum-to-dissimilar-material parts. After several years of developmental research, the c.BOND tool can now reduce total diffusion bonding process time essentially in half, and thus reducing the energy required during processing by as much as 30 per cent. This also improves the quality of the bond in certain instances.
In the traditional diffusion bonding process, a vacuum furnace provides radiant heat to the surface of the part. Subsequently the heat is conducted through the assembly and transmitted to the faying surface where required. However, when radiation becomes the dominant form of heat transfer, particularly at relatively lower temperatures in vacuum, below 600°C, aluminum’s thermal conductivity is time consuming.
Aluminum excels at conducting heat, particularly at lower temperatures, making it ideal for applications requiring efficient heat dissipation, such as in electronics and automotive components.
“Aluminum’s high reflectivity poses a challenge in traditional diffusion bonding. It’s like trying to heat a mirror with a spotlight—the energy is reflected away instead of being absorbed into the material [using the traditional diffusion bonding process],” says Horst-Gunter Leng, product manager with PVA TePla, a global manufacturer of industrial furnaces and PulsPlasma nitriding systems.
Leng adds that diffusion bonding of aluminum requires superior temperature control throughout the process. To prevent overheating of the load, slow heating rates traditionally are applied, leading to long process times.
In addition, aluminum alloys have a narrow processing temperature range for successful bonding. When temperatures fall outside that critical temperature band a poor bond is produced.
To overcome the existing challenges of bonding aluminum, PVA TePla and its partner initiated an extensive development program and came up with an innovative solution: integrating heating elements directly into the press platens, Leng explains. “This approach speeds up the bonding process, and significantly enhances efficiency by directly transferring heat to the aluminum components.”
The culmination of extensive research and development is the c.BOND machine, which features a unique combination of direct conduction heating through the top and bottom platens that are in contact with the assembly. This innovative design ensures bi-directional homogenous heating and more precise temperature at the bonding interface where it is required.
The c.BOND machine utilizes a hot-press tool with advanced software and feedback sensors to achieve micrometer-precise pressure control across the entire component surface. This ensures uniform bonding over large areas. Furthermore, the system allows for selective heating of specific areas, preventing unnecessary heat exposure to other parts of the component.
The high-vacuum atmosphere within the chamber eliminates contamination and prevents voids in the bonded joint.
The c.BOND technology demonstrates significant quality improvement of bonded aluminum components. PVA TePla says the technology improves temperature homogenity in the load by 70 per cent, which enhances bonding across the the entire surface; and that the technology improves the parallelism of parts by 50 per cent, which enhances the accuracy of geometric dimensions, tolerances and product specifications.
According to Leng, the c.BOND furnace technology by PVA TePla is commercially available today for high volume production. The innovative furnace technology incorporates another feature unique to the industry, utilizing PVA TePla’s proprietary automatic bonding software (ABP). “With the automatic bonding software, you place your parts in the furnace, input a few parameters such as the size of the bonding area and the software calculates automatically the optimum processing parameters. No specific diffusion bonding knowledge from the operator is required.”
He notes that the recipes can be modified according to the type of material being bonded, the thickness of the material, its surfaces, and other factors. During the process the software continuously monitors the process in real-time and adjusts parameters accordingly.
A c.BOND unit is installed at a national research facility in Germany, The Günter Köhler Institute for Joining Technology and Materials Testing (ifw Jena), an independent, non-university industrial research institution that conducts research in diffusion bonding, additive manufacturing, brazing, welding, laser processing, material science and other forms of bonding.
The c.BOND system is compact, requires minimal maintenance and enables high-volume production of aluminum components for diverse industries. Its benefits are being realized in aerospace, where it creates lightweight yet strong aircraft components. In the semiconductor industry, it provides a cleaner alternative to brazing, eliminating the risk of solder contamination. There is also growing demand for diffusion-bonded aluminum heat sinks, crucial for cooling high-power silicon carbide (SiC) electronics.
Diffusion bonding also has applications for conformal cooling. The concept is to bond layers of sheet metal that contain machined channel/microchannel structures. When combined, the channels provide a path for heat dissipation. Current applications include power electronics for effective heat management and rapid cooling of molds utilized in injection and blow molding processes.
With the size of components continually getting smaller in sectors like semiconductors and electronics, controlling the amount of time, and by extension heat, introduced into the part becomes more critical.
alu profiles This feature was provided by PVA TePla.