At Indium Corporation, we understand the challenges related to power electronics assembly; devices are increasing in complexity, while demands on performance and reliability grow stronger. On top of this, companies are searching for ways to increase efficiency/throughput. One technology helping to address those challenges is formic acid reflow soldering: a fluxless process that is proving to be a game-changer in power electronics assembly.
By removing the need for traditional flux, formic acid reflow enables oxide-free soldering with minimal-to-no residue, low voiding, and simplified post-process.
In this post, I will explore the fundamentals of formic acid soldering with you, no matter if you are thinking about adopting it, or are already in the process. This blog will cover topics like where it’s being adopted (particularly in semiconductor packaging, power modules, and LED manufacturing), the advantages it offers, and the challenges manufacturers should consider. We’ll also touch on how Indium Corporation is helping more and more manufacturers achieve success with this technology, with materials tailored for formic acid reflow processes.
What Is Formic Acid Reflow Soldering?
Traditional soldering depends on flux to remove oxides and promote good wetting on the soldering surfaces to ensure a strong joint is made. While this has been very effective in past decades, the use of flux introduces complexity. Flux leaves residues that often must be cleaned with chemical solvents—a time-intensive and environmentally-taxing process. Potential reliability concerns with uncleaned residues in high-power devices creates an even more critical challenge in these applications.
Formic acid offers a smarter fluxless alternative. When introduced into a reflow atmosphere—typically carried by nitrogen and activated at temperatures around 180°C—it acts as a potent reducing agent. It reacts with oxides, ultimately breaking them down into harmless by-products like CO₂ and water vapor, which can be removed from the reflow chamber via vacuum.
The result? A flux-free soldering process that requires no post reflow cleaning. It supports cleaner assemblies, removes reliability concerns related to flux residues, and improves throughput while reducing process steps.
Key Applications of Formic Acid Soldering
Formic acid reflow soldering is not a one-size-fits-all approach, but it has gained mass adoption in specific sectors and is now quickly gaining adoption in other sectors like power electronics assembly, where cleanliness, low voiding, thermal/electrical performance, and high yield are essential for success.
Semiconductor Packaging
Formic acid reflow soldering first found a natural home in wafer bumping and advanced packaging. These processes demand ultra-clean joints and low voiding to ensure device reliability. In fine-pitch applications, it is more challenging to clean the residue, and the residue can cause reliability problems. By eliminating cleaning steps, manufacturers save time and minimize risks associated with flux residues, which can lead to contamination in sensitive electronics.
Power Electronics Assembly
Modern power modules designed for demanding applications, such as inverters in electric vehicles (EV), operate at a high-power density and at high temperatures, so the solder interconnects must have maximum efficiency for dissipating heat. Formic acid reflow soldering, carried out with specialized solder preforms and solder pastes, provides low-void, clean, robust joints that excel in conductivity and thermal management. The need for cleaning is eliminated, streamlining the process flow in an environmentally-friendly way.
LED Manufacturing
High-power LED packages demand enhanced thermal dissipation, which is reliant on precise, low-void soldering. Fluxless soldering not only supplies the clean metal bonds that LEDs require but also simplifies their assembly process by removing the need for post-soldering cleaning. This approach yields better-performing LEDs while reducing production complexity.
Overcoming the Challenges
Like any newly adopted technology, formic acid soldering comes with a learning curve. Some of the challenges faced include:
Oxide Reduction Control: The effectiveness of the oxide removal depends on the fine-tuning of parameters such as formic acid concentration, flow rate, and soaking temperature of the thermal profile. The balance of thermal activation time and gas distribution must be carefully calibrated. For example, excessive concentration or exposure to formic acid can result in “new” solder defects like tin steaming.
Equipment Compatibility: Not all reflow ovens are capable of formic acid reflow. Modification is possible in some cases, but for most, an investment in purpose-built reflow systems will be necessary.
Material Selection: Some materials will not react optimally under formic acid atmospheres, so it is important to select solder materials specifically designed for this process, like the Formic Acid Soldering Technology (FAST) product suite from Indium Corporation.
Process Development: Transitioning from flux-based soldering to fluxless with formic acid isn’t plug-and-play. A deep understanding of the formic acid reflow process and a carefully designed system is necessary to successfully adopt this technology. Leverage Indium Corporation’s expertise in this process to accelerate adoption and the introduction of new products to the market.
Indium Corporation: Enabling the Transition
At Indium Corporation, we’ve embraced the potential of formic acid soldering with fluxless products, both proven and newly developed, especially for power electronics assembly. We are actively supporting its adoption through our Formic Acid Soldering Technology (FAST) platform. From preforms and pastes designed for formic acid reflow to innovative tacking agents that simplify the assembly, our product portfolio is engineered to meet the demands of this cleaner, next-generation approach. In our next post, we’ll dive into the specific material options that Indium Corporation has developed for formic acid reflow soldering, enabling manufacturers to power forward with this cutting-edge technology – so stay tuned.
To learn more about formic acid soldering, read our Whitepaper on the topic!
