We use hot air leveling (HAL) process in pcb production. HAL process is 3 steps. �n 1. step flux. 2. step is HAL. And 3. step is rinsing. As you know there is mustn't any flux after rinsing operation. Our flux chemical is water soluable. But there are flux residue on some pcbs after rinsing. What's your suggestion? Using a brush during rinsing. or put some cleaner in rinse water. Another thing that we maybe use cleaner after HAL. I mean we should put all soldered plates in cleaner soluation in a container and wait for a while before rinsing operation.
water alone especially cold is not good enough, how do you check for hasl fluids when most residues left behind after improper cleaning are non ionic. Use 40C saponifier followed by heated rinse then cold rinse then DI rinse followed by dry.Nylon brushing is OK as long as fed with hot saponifier as well.No cold water as flux could gel and harder to clean off best of luck
About one year we have that problem with some of pcbs. Our customers told us about that. Because they can't mounting components on those pcb reason of flux residue. As you know flux not conductive chemical. We didn't change anything before having that. Now we think that we must change operating system of rinsing process. Sorry for late reply.
The water soluble flux residue is staying there because the rinsing temperature it may be too low. The flux needs about 130-140 degrees celcius to become soft. If you are using water soluble flux, as per IPC A 610 standards it needs to be remove completely from the assemblies. Hope this helps.