Tips on Creating an Effective Formic Acid Reflow Process

Fluxless reflow with formic acid offers numerous benefits, including higher yields by eliminating flux-related defects, reduced floor space requirements with the removal of flux-related equipment, as well as reduced energy use and operating costs.

While setting up a formic reflow process is similar to a standard reflow process, there are a few additional things that one should keep in mind. Below are a few tips on setting up an effective formic reflow process.

• A sufficient soak or dwell period is necessary in a formic reflow profile. One should target a soak to occur between 150-180C, because this is the optimum temperature which formic acid vapor chemically reacts with metal oxides.
• Application where solder is covered by a device, such as a die attach, a slightly longer soak may be required than if the solder was openly exposed to the formic, such as bumping reflow.
• Formic acid vapor should be injected into the oven near the soak zones, and a proper formic acid profile should have the highest formic acid concentrations at the soak zones.
• Formic acid vapor should be minimized at the oven’s reflow zones. Formic acid is not needed here and has been known to be associated with unwanted formate crystal growth.
• Low O2 ppm levels are essential for a quality formic process. Ensure that O2 levels are <20ppm for all oven zones.

The main indicator of a good formic reflow process is whether proper wetting of the solder is occurring. If you determine that wetting is not sufficient, a longer soak period or higher formic concentration can help. A proper formic process may take a few iterations to key in on the optimal parameters.

Read more – Heller’s Fluxless Formic Reflow Ovens.