Thermogravimetric Analysis of Flux Solvent Evaporation in Reflow Profiles
Thermogravimetric solvent mass loss below half a percent prior to liquidus eliminates outgassing macro-voids under bottom-terminated components.
Organic Acid Activators
Flux chemical properties
Carboxylic acids or their derivatives form the base chemistry used to reduce metal oxides on board surfaces during soldering. Organic acid activators perform this role by reacting with contaminants and tarnish at elevated temperatures to expose clean metallic contact points. Thermal energy drives the dissociation of these compounds into active ions that dissolve oxidation layers while the remaining carrier material stays liquid to prevent reoxidation.
This process leaves residues that are water soluble and conductive unless removed by an aqueous cleaning cycle.
Thermal reaction kinetics
Heat triggers the conversion of dormant activator molecules into reactive agents that attack metallic oxides on copper pads or component leads. Application occurs primarily in flux formulations for wave soldering or selective soldering where the board travels through a molten metal wave. High temperatures drive the chemical reduction of oxides to metal, and the speed of this reduction depends on the concentration and molecular weight of the acids present.
Slow degradation of the activator allows sufficient time for complete wetting before the solder cools into a solid joint.
Residue management
Aqueous washing systems provide the primary method for extracting activator byproducts from the assembly after the joining process finishes. Ionic contamination levels drop significantly when deionized water dissolves the polar acid components from the board substrate. Residual material left behind creates paths for electrochemical migration that eventually cause shorts or corrosion between high density tracks.
Proper cleaning verification requires extraction testing to confirm that the conductivity of the rinse water stays within acceptable limits for long term reliability.