I recently etched 2 PCBs, out of 'necessity'. I don't plan to do this often, if at all, but it was an interesting experience. All the traces seem to be correct. I've started to solder in the components, but most copper traces are still bare. If I finish the effects within say 2 weeks, no mods afterwards, would that be fine? Or would the copper keep corroding until at some point the effect becomes noisy or defective? Should I seal the copper before I continue, or just clear coat it afterwards?
Thanks mucho!
It will oxidize some after a couple of weeks and may become more difficult to get solder to adhere to. But, I doubt it will be ruined.
Agreed, seems like you could always clean the traces where you're going to solder if absolutely necessary. If I had a board etched I wasn't going to get to for a day or two (which is rare ;)) I would put it in a small ziplock back and seal out the air to help preserve it.
You don't need to "protect" it, as such. But the oxidation buildup can interfere with things you may want to do after you've built it.
For example, you may find that it's very close to what you want, but would be so much better if you swapped out this cap for that one. Unfortunately, the cap type you have in the value you want to use has a different lead spacing than the original layout called for, so your only alternative (since, of course you have a gig that night :icon_wink:) is to quickly pop another hole in the board, install the other cap, and bend the lead over so that it comes into contact with the required trace. That trace needs to be solderable.
When I make a PCB, once it is etched, I buff it clean clean clean, and wipe some liquid flux all over it. Then, I tin it so every trace and pad on the entire board has solder on it, and clean the flux off. Takes a little extra time, but EVERY trace and pad remains usable for a long time, permitting "after-market" changes at will. It's not everybody's cup of tea, but it works for me.
Incidentally, the liquid flux acts as a temporary shield against oxidation. So, you can etch your board, coat it in flux, and then wrap it in plastic wrap for working on at some later point.
I've made boards and not used them for over a year, maybe 2. I just clean them again with acetone and give them a hard buff with steel wool until shiny and they come out fine.
The bad scenario is when you start a board but don't finish it. You can't buff a half populated pcb. If I have a boad that I can finish right away I just solder a blob onto every empty pad and then desolder them. This tins the pads and keeps them from oxidizing.
I use MG Chemicals liquid tin on all of my bare copper boards before storing, or if it's a new board, before soldering. It's pricey, and I avoided spending money on it for several years, but it's well worth the price for the protection it provides to the boards, the ease of soldering, and how little you use.
http://www.mgchemicals.com/products/421.html (http://www.mgchemicals.com/products/421.html)
I've also done the tin every trace with solder thing, though that can get tedious on a large board. A fellow I know who used to work as an electronics tech told me to use clear nail polish. Seems to work and is easier than tinning. I'm sure there could be some issues with fumes if I'm doing any further soldering on the board, but I've got a fan blowing solder fumes away already.
I usually just spray a light coat of lacquer on the PCB after I drill it. You can solder through lacquer without issue. I used to use Humiseal which is a solderable conformal coating, but was told by the manufacturer I can get the same thing out of regular spray lacquer if using a light coat.
Can oxidation ever bridge a connection or is it just a solderability issue that scrubbing can resolve?
Quote from: MoltenVoltage on June 01, 2011, 02:59:43 PM
Can oxidation ever bridge a connection or is it just a solderability issue that scrubbing can resolve?
I don't believe oxidation will bridge a connection since it mostly eats up the copper. I had an old Big Muff that stopped working after a trace was eaten through and corroded. Tin whiskers from lead-free solder can certainly bridge connections. Or is that a myth?
I give a light coat of this stuff after etching.
http://www.jaycar.com.au/ShowLargephoto.asp?id=1873&PRODNAME=Circuit%20Board%20Lacquer%20Spray%20Can&IMAGE=
+1 clearcoat....when tested thoroughly.... ;)
Even before etching a PCB, make sure it doesn't slide over another PCB or you will get scratches in the copper that may cause opens in etched lines. Bag them individually before and after etching. If you use solder plating, don't skimp on the lead. At one place where I worked, we received boards with bright shiny tin plating that were solderability nightmares whereas the duller solder-plated boards soldered perfectly.
I've been tinning mine for awhile now. Every once in awhile I get fancy and do a screened lacquer coating, but I dig the way a tinned trace looks.
I use my larger 40W iron for tinning. Just like Mark says to do... paint on some flux and hit the iron with some solder. The hotter iron makes it flow nice and fast, and the larger tip holds enough solder to tin a 1.5"x2" board before I have to clean the crusties off the tip and reload.
I found that tinning also helps align my bit when I drill, after deciding that tinning after drilling was a pain (pad holes close up on you). ;D