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Post Process PCB

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Hi, I'm making my first PCB with a CNC, I was wondering what I need to do to it after I mill it? I have read about things like tinning, or nickel gold plating boards, but if I understand it correctly, this is solely to help shelf life i.e. the time that the boards can sit around prior to getting soldered and then shipped. In my case I plan on soldering it immediately so I don't care about shelf life so for me it's more of a question of how to protect traces to make sure they don't disintegrate over time.
 

spec

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You can't leave the copper exposed: it will corrode. But worse still, with certain airborne/surface contaminants it can grow crystals and form a short between tracks. Copper is normally electroless nickel plated, but you can just about get away with a conformal coating for a non demanding low impedance circuit, but it is not advisable. If it is fine surface mount construction you have no option but to plate.

I had a nightmare once when a cheap commercial board lost part of its conformal coating. The circuit would work fine for a few days after cleaning but then it would slowly produce faults. We could not figure what was going on, but under a microscope you could see that fine cystals had grwn between some tracks. So, in the end, we cleaned the board and conformally coated with epoxy. After that the circuit was OK.

spec
 

spec

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But tin oxidises as well. Or is this good enough to protect the copper below?
To be honest I do not know, but I think tin is good enough. This requires a bit of research unless one of the ETO PCB experts can advise further.

spec
 

DirtyLude

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How long do you want it to last and how critical is the application?

I have etched a lot of boards in the last 12 years without coating them and none of them have failed. Cleaning up a couple months ago I found the 1st board I etched in 2004. Haven't tested it, but it looks like it would still work.

I have some conformal coating in a can I use to spray anything that works in a humid or wet environment. I think that would be enough if you are just using these boards yourself.
Hobbyist, not a professional here, though.
 

JonSea

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Unless they are in some kind of corrosive environment, uncoated copper should be fine. I have a 20+ year old home etched circuit board that's working fine.

Outdoors or close to the ocean would be be a different situation.
 
It's a PCB that will be inside my CNC controller box. I guess I want to last as long as possible and also want to make sure there's no short anywhere otherwise the magic smoke will kill a lot of components... PC, CNC etc. Plus it's a CNC, so I want to ensure there's signal integrity to make sure it doesn't do anything unexpected.

I'm just a bit confused since all coatings - tin, nickel/gold etc they all have a shelf life so it seems there's no solution to protect a PCB, they all just wither with time.
 

spec

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It's a PCB that will be inside my CNC controller box. I guess I want to last as long as possible and also want to make sure there's no short anywhere otherwise the magic smoke will kill a lot of components... PC, CNC etc. Plus it's a CNC, so I want to ensure there's signal integrity to make sure it doesn't do anything unexpected.

I'm just a bit confused since all coatings - tin, nickel/gold etc they all have a shelf life so it seems there's no solution to protect a PCB, they all just wither with time.
I have seen professionally made PCBs (electroless nickel, solder resist mask) that are 30, or so, years old and work fine. They also look OK, but the solder joints, instead of looking bright, are very slightly dulled.

Do you have fine traces that are very close together and do the traces pass under components or otherwise are in trapped air? If so, I suggest that the board need some protection, especially in view of the critical application and environment (machine shop).

spec
 

JonSea

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Here is a wonderful circuit board I hand etched about 38 years ago that has been hanging in open air in the laundry room ever since. The copper has been protected in no way. As I said, in a non-corrosive environment, bare copper circuit boards will survive a long time.

20161117_234354.jpg
 
No worries guys, thanks, looks like I can leave it at that. It's not going to have tiny traces, I'm making everything as big as possible... less headaches working with high precision.
 

spec

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No worries guys, thanks, looks like I can leave it at that. It's not going to have tiny traces, I'm making everything as big as possible... less headaches working with high precision.
Good luck.:cool:

spec
 

KeepItSimpleStupid

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A mix of vinegar and salt will clean the PCB really nicely. A clean PCB is easier to solder.

There is HASL Hot air solder leveled, nickle-gold and tin coatings.

I've done this: Heated the board in "peanut oil" suspended somehow. Just make sure it doesn't sit on the bottom. Then I could melt tin-lead solder and spread it with a damp rag. The peanut oil is hard to get off and I would not do it to a sensitive board. Do this sort of plating before you drill.
I don't have a heat gun yet!

Some oxides,like Aluminum are self-limiting. Nickle and tin are self-limiting. Copper is not. https://www.copper.org/applications/industrial/DesignGuide/failure/oxidation04.html
 
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