Indium Corporation has outlined formic acid reflow soldering as a core process technology within its semiconductor packaging and assembly portfolio. The approach positions formic acid as a gaseous reducing agent that removes surface oxides from solder and substrate metallisations during the reflow cycle, enabling void-free, flux-free joints without the post-process cleaning steps associated with conventional fluxed assembly.
In standard reflow soldering, flux chemically activates the metal surfaces to allow proper wetting. However, flux residues can pose reliability risks in hermetically sealed packages, MEMS assemblies and fine-pitch flip-chip interconnects, where even trace ionic contamination or outgassing may compromise long-term performance. Formic acid vapour, introduced into a controlled oven atmosphere, reacts with metal oxides at elevated temperatures and exits the process chamber as a gaseous by-product, leaving no ionic residue on the assembly.
The technology is listed by Indium Corporation in the context of several advanced packaging application areas: 2.5D and 3D packaging, ball-attach and bump fusion, die-attach, flip-chip, MEMS assembly, system-in-package (SiP) and heterogeneous integration assembly (HIA). These application segments represent some of the most demanding interconnect challenges in current semiconductor manufacturing, where joint geometry, metallurgy control and contamination management are critical process parameters.
From a European electronics manufacturing perspective, the relevance of formic acid reflow is growing as packaging complexity increases. Heterogeneous integration — combining chiplets, interposers and embedded dies within a single package — demands solder processes with tight control over voiding, standoff height and oxide reduction without introducing flux chemistry that may be incompatible with sensitive device materials or hermetic sealing requirements.
Equipment suppliers active in the European market, including Rehm Thermal Systems and Heller Industries, have developed reflow ovens with integrated formic acid atmospheres, indicating that the process is transitioning from laboratory-scale to higher-volume production environments. Solder material selection remains critical: indium-based and tin-based alloys in preform or paste format are typically paired with formic acid atmospheres, with the choice of alloy influencing the temperature profile and reduction kinetics required.
Indium Corporation's positioning of formic acid reflow alongside thermal management materials — including TIM1, TIM1.5 and TIM2 interface materials — and immersion cooling reflects an integrated approach to the thermal and interconnect challenges of high-density packaging. As power densities in AI accelerators, RF modules and power electronics continue to rise, flux-free soldering processes that support both electrical reliability and thermal performance are expected to see increasing adoption across advanced packaging lines.
