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 Flux Vehicle
Chemical Composition
Solder paste formulations contain a complex carrier medium that suspends metal alloy powder and provides chemical cleaning action during heating. An organic flux vehicle typically comprises resins, solvents, and activators that govern the rheology and printability of the paste before soldering. This vehicle must evaporate or decompose during the reflow process to leave a clean solder joint.
Thermal Deposition
Heating the solder paste drives off the solvent phase of the carrier to prepare the metal particles for melting. As the organic flux vehicle heats up, its viscosity drops, allowing the solder alloy to coalesce without restriction. If the vehicle is too stable, it will not decompose, preventing the solder alloy from wetting the copper pads.
This situation causes weak mechanical joints that fail when subjected to electrical and physical loads.
Residue Management
Cleaning the printed circuit board after soldering removes the remaining chemical byproducts left by the carrier. The leftover organic flux vehicle residue can cause corrosion or electrochemical migration if it remains on the board surface. Depending on the paste type, operators use either water wash or chemical solvents to dissolve these residues.
In no-clean formulations, the residue is designed to be benign and non-conductive, requiring no washing step. This choice of paste simplifies post-reflow processing while maintaining the electrical integrity of the board.