What is Solder Flux?
In soldering, flux is a substance that removes the oxide layer from metal, so that the solder can flow and bond effectively. In fact, the word “flux” comes from the Latin word for “flow.”
There are two primary types of flux used in PCB assembly: water-soluble and no-clean flux.
Understanding Water-Soluble v. No-Clean Flux in PCB Manufacturing
Water-soluble flux was the industry standard for years. The material is usually solvent-based, with a high solid content. It is highly active, with a long life, which provides excellent soldering performance by effectively cleaning the metal to be soldered. However, there’s a big challenge: the chemistry is aggressive and corrosive, and it leaves a residue on the board.
No-clean flux, on the other hand, leaves a negligible amount of inert residue on the PCB assembly and leaves little to no active chemistry on the board after soldering. No-clean fluxes have low solids, and they can be alcohol-based or water-based. (Alcohol-based flux may or may not contain rosin, and water-based no-clean flux isn’t necessarily water-soluble or washable.)
Comparing Residue Impact: Water Washing v. No Cleaning Required
Because water-soluble flux is active and long lasting, the residue continues to react on the board after the soldering process is complete. This means the residue needs to be cleaned off with a water wash, and this machine wash process must be thorough to ensure clean circuit assemblies.
No-clean flux, in most cases, eliminates the need for a cleaning step, because there is essentially no residue or active chemistry remaining on the PCB assembly after soldering.
The Efficiency & Cost-Effectiveness of No-Clean Flux
The need to use a water wash system to clean the PCB after soldering with a solvent-based, water-soluble flux adds another step into the manufacturing process. This can be less efficient and can add cost.
No-clean flux streamlines the PCB assembly process. Cycle time is shorter, for greater efficiency, and the process may be less expensive to the customer. Another advantage is that alcohol-based fluxes evaporate quickly, which reduces flux spattering during soldering.
Optimizing Your PCB Assembly Project with the Right Flux Choice
The soldering choices for a PCB assembly project are surprisingly complex. At ETI, our team has the ability to offer you both no-clean or water-soluble flux, depending on the requirements of your project. Feel free to contact us, and we can discuss the process that works best for your product and application.