1
\$\begingroup\$

I am designing a pcb which I have some mounting hole with the function to connect the mounted screw to the PCB ground.

I found good resources about this subject in the blog, like this one and this other.

However, there is one point that I am still in doubt: I was thinking about the possibility that, after a long time, the interface between screw head and mounting hole pad goes into oxidation.

Just the correct screw tightening is enough to prevent oxidation process? Or there is specifics combinations of screw's material and pcb pad finalization I should choose to avoid oxidation?

If possible, I would like to avoid golden plating, for cost reasons.

\$\endgroup\$
  • 2
    \$\begingroup\$ Yes If the surface is exposed to air with sufficient pressure to prevent air (gas from touching conductor surface it is called "gas-tight" then it will not oxidize. Hwoever incompatible metals can corrode from galvanic , so tin plated copper tracks (HASL) or other PCB surface finishes to prevent copper oxide. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 10 '18 at 14:42
  • 3
    \$\begingroup\$ Crinkle washers. \$\endgroup\$ – Andy aka Jul 10 '18 at 15:02
  • 2
    \$\begingroup\$ Star washers impose greater pressure with less torque. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 10 '18 at 15:11
1
\$\begingroup\$

Eventually oxygen will migrate everywhere, having the terminals mated together will stop this process, but if there is a micro gap the oxygen is much smaller and will eventually diffuse into the gap.

Get an ENIG coating instead of bare copper

Or use deoxit and clean it periodically

The real question is: is it going to affect your signal? resistance will but the worst thing is thermal noise from the junction. If you're not concerned about turning your junction into a thermocouple and only about resistance its probably not going to be a big deal, just size your contact bigger.

\$\endgroup\$
  • \$\begingroup\$ Thanks for the reply. I will use it as a high frequency bond, to absorve the current induced in a heatsink by a mosfet switching back to the ground plane. So the total resistance is actual a concern, but since the contact was not or almost not totally oxidated, that is not a big problem for me. Thanks! \$\endgroup\$ – Luis Possatti Jul 11 '18 at 16:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.