Read our PCB engineers reply to a customer's query below.

Q: Looking to buy some flux from your company, if you could advise which flux is best for me. I am currently repairing pcb electronics, vehicle electrical parts like instrument clusters. The flux I currently use works well but if you revisit the pub after 1 or 2 months there's green residue over the area flux was used. It's eating away at the small resistors and is self damaging over time. Can you advise why this is happening and a suitable product from your shop that guarantees safe working with pcb electronics without the flux turning into green corrosive residue Iver to.e

A: Fluxes by their nature can be chemically aggressive which helps to remove oxidisation from metals which allows the solder to “Wet” the surface. It may be that the current flux being used is of the type which is recommended to be removed by chemically washing or ultrasonic cleaning. This is fine to use to achieve a good solder joint but would need to be cleaned off after soldering.

 

Please see below an Aerosol PCB Cleaner

https://www.pcb-soldering.co.uk/aerosol-pcb-cleaner-400ml

 

Flux removal fluid for use within an ultrasonic cleaner

https://www.allendale-ultrasonics.co.uk/flux-remover-and-pcb-ultrasonic-cleaner-solution-1-litre-cleaning-fluid

https://www.ebay.co.uk/itm/Ultrasonic-Cleaner-PCB-Flux-Removing-Fluid-1L-Cleaning-Solution-Rework/302993143979?epid=1405441056&hash=item468bcc78ab:g:jlMAAOSw0J5gD3Bs

 

There are fluxes available which are classed as “No Clean” these can be used and left in place throughout the PCB service life. Please see the link below.

https://www.pcb-soldering.co.uk/sra-no-clean-tacky-flux-10cc

https://www.ebay.co.uk/itm/Tacky-Flux-10cc-Made-in-USA-Low-Odor-No-Clean-Ideal-For-Soldering-Rework-PCB/232235745309?epid=1336899981&hash=item361254401d:g:OfwAAOSwJqpgDuVi

 

The other alternative is to coat the PCB once repaired with a protective PCB lacquer This is a belt and braces approach but will ensure the PCB isn’t affected by the humidity changes within a damp environment and prevent corrosion and Electrochemical migration which can form as dark patches forming resistive shorts on a PCB which pull down power supply rails.