Pre-cleaning boards before soldering

[kalel]

I mostly do very simple THT soldering on protoboards or kit PCBs. Some videos suggest cleaning the copper on the kit boards before soldering, usually with a fiberglass brush.

Is this an step to do in order to get better solder joints, and if so what tool do you recommend?

[rhb]

I use hand dish detergent and a new green 3M brand scrubber.  But fine (e.g. 240)  grit sandpaper will do.  You want a fresh bright copper surface.  Generic green kitchen scrubbers from China don't have any abrasive and won't do a good job.

Steel wool doesn't do a very good job and leaves little bits of metal around. Brushes are not very thorough.

[AndyC_772]

I wouldn't try and scrub a PCB clean before soldering. The exposed copper should already be coated with gold, tin, or some other finish to protect it from oxidation, and unless the board is very old, it should solder just fine with a suitable flux.

Plain copper stripboard is different, though. I usually give any stripboard a thorough clean with fine steel wool, which is way too abrasive to use on a PCB, but works well at removing the inevitable oxide layer that builds up on exposed copper.

[kalel]

I wouldn't try and scrub a PCB clean before soldering. The exposed copper should already be coated with gold, tin, or some other finish to protect it from oxidation, and unless the board is very old, it should solder just fine with a suitable flux.

Plain copper stripboard is different, though. I usually give any stripboard a thorough clean with fine steel wool, which is way too abrasive to use on a PCB, but works well at removing the inevitable oxide layer that builds up on exposed copper.

With protoboards (those that have holes and copper around them) and stripboard you're right, there's only copper. But also on some kit PCBs there's only copper (edit: actually some are tin plated). Anyway I am mostly asking about the boards that do have copper exposed.

[Arjen_Arg]

I agree with the others in that cleaning may do more harm than good. But, if you are working with cheap prototyping boards that don't have any finishing or solder mask, then, using steel wool will help remove rust and dirt.

[rdl]

I don't know what's available where you live, but look for some mildly abrasive kitchen/bath cleanser. You might already have some. Here we have brands such as Ajax and Comet (and generic types also). Copper, when very clean and shiny, has a distinct pinkish color, and this type of cleanser will polish bare copper very well. Be sure to rinse well because there's bleach and stuff in the cleanser.