Flux Chemistry
Soldering chemicals containing water soluble organic compounds serve to clean metal surfaces by removing oxides at high temperatures. An organic acid flux typically relies on substances such as citric or glutamic acid to provide the necessary activation without the use of halides. These formulations are popular in high-volume assembly because they offer excellent wetting and leave residues that are easily removed with deionized water.
The lack of rosin allows for a very clean board appearance after the washing cycle.
Residue Conductivity
Severe reliability risks arise if polar residues are left on a board surface after processing. The Residue Conductivity of organic acid flux poses a threat by promoting metal migration. Because these acids are highly polar, they quickly attract moisture to the surface of the printed circuit board.
This creates an electrolyte that promotes localized corrosion of the circuitry. Strict monitoring of the wash water resistivity ensures that all active chemical species are neutralized and removed.
Thermal Stability
Duration limits for the preheat phase depend on the Thermal Stability of organic acid flux. These acids tend to decompose or volatilize more quickly than traditional rosin activators. Optimized oven profiles balance the need for drying with the requirement to keep the chemistry active.
