Flux is an integral part of all solders (both paste and wire). Flux facilitates the proper flow and wetting of component leads onto PCB pads. Flux leftovers can occasionally lead to contamination or even electrical migration between component leads (leading to shorts) on the PCB. High reliability systems such as space, military as well as other mission-critical applications - usually demand the cleaning of so-called “No Clean” fluxes. PCB cleaning is often needed for these types of circuit boards. Salespeople at Restronics Northern California have years of expertise in various forms of flux cleaning... from benchtop flux cleaning sprays to higher volume batch cleaning machines and chemistry to eliminate flux residues. By reviewing the existing process and providing appropriate recommendations for improvement, we can reduce the human labor necessary for hand spray cleaning and ultimately improve reliability and cleanliness by employing a DI water based batch cleaner with aqueous chemistry.
The majority of US manufacturers make high reliability PCBs, so flux cleaning is essential. Cleaning circuit boards with solvents, while extremely effective, can be highly hazardous for the surroundings and for humans. Due to increasing restrictions on solvents used in Vapor Degreasers, companies are switching from solvent based cleaning to aqueous based flux cleaning. Cleaners based on aqueous liquids are often zero-discharge, which indicates that no residue or wash solution goes to the drain; it stays in the machine. Generally, wash chemistry is a combination of DI water and cleaning chemicals.
The suitable cleaning chemistry must fit the composition of the soils as part of PCB cleaning (could be oils, flux residue, or other contaminants). Most people try to utilize a simple alcohol cleaner but it typically causes a white sediment and doesn’t remove flux. This is particularly challenging when clients need to conformally coat the PCB. Generally, conformal coatings will not adhere effectively unless the PCB has been cleaned properly. Prior to applying conformal coatings to military and space applications, all flux residues must be cleaned and tested with an Ionic Contamination tester.