SOFCs are made up from different materials depending on the requirements for the fuel cell, but always consist of an anode, cathode, and electrolyte in a sealed cell. In many cases, and in particular for planar SOFCs, an effective way to seal the fuel cells is to use the screen print brazing method, which is an automated process that ensures that the brazing material is applied only to the areas where it is needed.
Höganäs works alongside SOFC manufacturers that were previously struggling with the process not due to the technology, but to the brazing paste itself. The materials used in the past were not able to offer the sort of consistency and robustness that makes this process as efficient as possible, so Höganäs worked alongside them to offer a better alternative.
More than metal
The quality and effectiveness of a brazing paste is not just dependant on the brazing filler metal powder used. Both Höganäs SOFC customers had previously struggled to find a paste that provided the required performance, despite the base metals being common and widely available. Höganäs listened to their challenges, mainly revolving around the consistency of the pastes and the shelf life, and provided test samples to see if improvements were possible.
Following the test period, the customers saw that the Höganäs brazing pastes were more robust, easier to apply and more consistent in the way that they coated the required areas. In addition to this, the shelf life of the pastes is often a minimum of one year as opposed to the storage period offered by competitors, which in many cases is considerably shorter.
“We provided one of our customers with a BrazeLet Ni9P-9003 sample, which is a nickel-based brazing paste,” says Lisa Kjellén, Director of Brazing Development for Höganäs. “The problem they were facing was mainly to do with the consistency of application. The application of the previous paste often had to be checked and adjusted as the screen printing process wasn’t evenly covering the joining areas equally every time. This meant slowing or stopping production, manually fixing the application, and resuming. Upon trying our solution, they saw that it was applied as desired every time, meaning production could continue without interruptions.”
The reason for the difference is that Höganäs uses fewer ingredients and tests products extensively, often alongside customers and potential customers. For screen print brazing, consistency and robustness are essential qualities, as the joints and seals that the brazing process provide are crucial to the performance of the fuel cell.
An iterative process
Every screen print application is different, and SOFCs have specific requirements that must be met. It’s not always the case that an off-the-shelf product will be the ideal fit, so testing and tweaking are essential parts of the journey towards an optimal paste. During the process with each of the SOFC customers, it was important for Höganäs to listen and understand the challenges, as only then is it possible to offer the ideal solution.
It’s also a benefit if the tests can be carried out quickly and efficiently, and thanks to the scale of Höganäs in combination with multiple Customer Development Centres, this is always a possibility.
“Working with the Höganäs team has been extremely successful and has been a positive experience all-around,” explains one SOFC brazing paste customer. “The development on the new paste was easy, and it has been performing very well for us.”
For a manufacturer, changing brazing paste can be complicated as it involves a new qualification process, but the benefits seen in the testing outweighed this short-term drawback. The benefits of using Höganäs screen printing brazing pastes include improved yield after brazing, less leakage after brazing, a stable and efficient printing process, a longer shelf life of the brazing paste, fast sampling and great, global support network.