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Prevent rust on a PCB? Answered

How do I prevent rust?  Or should I just not worry about the rust? 

I am using single sided board etched with ferric chloride, if that matters.

Also I need the copper to conduct "on the top", like if I put a multimeter on a trace it would still conduct.  So I can't use something like a clear coat spray paint.




Best Answer 8 years ago

A pcb won't rust its copper. Copper can corrode. Clean it throughly before soldering. Use rosin core solder. Keep liquids especially acids away from it.

It must me corroding, because it turned a "darker" color. Thank You AI

Pcbs will almost always take on a darker color on the copper. It's a natural corrosion action that actually acts as a protectant from the atmosphere.

IT's usually safe unless your 'atmosphere' is more harmful than most.

use liquid tin,that would help

I have had experience with protecting circuit boards from "rust". Once, at a cable company that had circuit boards located outdoors in a "protective" box. The board controlled charging of batteries and other functions. Problem was HUMIDITY, FOG, SNOW, and wind-blown moisture would get INTO the protective box and cause "rust" corrosion (electrolysis) damage to the boards. We sprayed the boards with protective plastic coating.... but THAT did NOT fix it. Finally, we wrapped the boards with a couple layers of plain clear packing-tape like that used to ship boxes. THAT fixed it. However this was only practical because the circuit boards had no components that got very hot. The 2nd place i had experience was with a circuit that had an EXTREMELY high impedance circuit that would stop working properly if SLIGHT moisture would get onto the circuit board. You could actually just blow your BREATH onto the circuitboard and it would STOP WORKING for a minute untill the moisture from your breath evaporated away. a spray coating of plastic spray fixed this problem on that board. THOSE 2 situations are good examples where moisture protection is called-for. Most electronics do not need such protection because they are used indoors in a controlled dry environment. If you are worried about the slight discoloration of copper foil-traces.... due to cosmetic reasons.... i think you are worried over NOTHING.

You can buy a tin plating solution, which will prevent the copper from oxidizing, but which is still conductive and solderable. You have to use it after the PCB is etched, but before you put the components in. I have seen it in powdered form as well as liquid. Do a search for Tinnit.

Unless your equipment is outdoors by the sea or exposed to some other corrosive environment you shouldn't need to take any special steps. (virtually no consumer electronics apply anything to their boards to stop corrosion.) However if you want to keep them looking thier shiniest you can spray on a coat of polyurethane. This guy over at the Adafruit forums ran a long-term experement and found it worked very well.  Read the thread for what kind gives best results.

Rust is iron-oxide, copper will corrode/oxidise though, lacquer / "varnish" might help?