A simple PCB question

[zener]

What is that coating (usually green) on the solder side of a pcb of manufactured electronic stuffs? Pardon my ignorance, is it some sort of a laqcuer?

Is it a must to have that coated under your PCB always or you can do without it and the pcb will last for a loooooong time?

Are there any sub for that?

Thanks for any help :wink:  

Zener

[R.G.]

It is solder mask, a layer of stuff that solder won't stick to and that protects the copper from being solder except where there are holes in it. The holes are aligned over the copper pads so you can run a wave of molten solder over the whole board and solder the whole thing at once. It's there for high volume manufacturing.

It has the side effect of preventing some solder bridges when hand soldering.

It has in general no effect on the longevity of the copper traces.

[Peter Snowberg]

It has in general no effect on the longevity of the copper traces.

I must respectfully disagree. Depending on the environment the board is in, the solder mask is the difference between lasting and not if the board doesn't have a tin over copper coating. I would say the effect is enormous.

I spent many years in embedded control applications where boards were subjected to nasty environments. Prototypes without any coating would fail over time (sometimes not a long time at all) where their coated counterparts would not fail.

I also have experience repairing systems that were soldermask coated but hand soldered. In some of those cases the uncovered copper corroded badly while the copper that had either solder or soldermask over it looked just fine.

If you want a home-brew board to last a long time, coat all the copper with solder (a very thin coating is fine).

Take care,
-Peter

[zener]

If you want a home-brew board to last a long time, coat all the copper with solder (a very thin coating is fine).

Take care,
-Peter

Meaning I'll just trace the copper traces with solder? :roll:  Then I'll have to stock lots of solder then :wink:  

By the way, how is that solder mask applied, paint brush, spray or the one side of the pcb soaked in it. Is it bought in retail packaging like bottle or plastic container or it's just for electronics manufacturers and stored in tanks.

[R.G.]

I spent many years in embedded control applications where boards were subjected to nasty environments. Prototypes without any coating would fail over time (sometimes not a long time at all) where their coated counterparts would not fail.

I also have experience repairing systems that were soldermask coated but hand soldered. In some of those cases the uncovered copper corroded badly while the copper that had either solder or soldermask over it looked just fine.

You are entirely welcome to respectfully disagree.

In harsh environments, it is absolutely true that unguarded copper gets eaten. In fact, in some environments, anything not potted and hermetically sealed gets eaten.

However...

I respectfully disagree with your disagreement for the limited environment that DIY pedals get used in.

For the limited environment of pedals used for music making,  most of the things that eat copper traces do not occur. The copper will look bad, turn green, etc. but the pedal will work perfectly well. I recently ran into the first PCB I ever made. It's a 1971 vintage, going on 33 years old now. The copper's brown, and green where I didn't have the sense to clean off the flux, but the circuit works fine.

Obviously there aren't any absolutes here.

By the way, a neat trick to tin copper boards is to use a 4" wide length of brass pipe, about 3/4" diameter, well tinned with solder, and heated internally with a propane torch until the  solder flows. Paint the board with liquid flux, lay it trace side up on a heat resistant surface, get the heated pipe all loaded with solder and swipe it across the board - not quite roller tinned, and you'll have to do some touchup, but it's pretty good for a home deal, and much better than hand tinning.

[Peter Snowberg]

In the limited context of DIY pedals being used in clean environments (no beer inside the pedals please) and where they are stored without excess humidity, I must respectfully agree with your respectful disagreement with my respectful disagreement.

I'm very anal about my building habits and subscribe to the notion that a system that is a little unreliable is like a woman that is a little bit pregnant. It's a hard habit to shake and it biases my answers.

Cool trick on the DIY roller tinning.

For hand tinning, a bottle of liquid flux makes things much easier and results in the use of less solder.


Just melt a thin coating of solder over all the traces and they're be protected for the next 100 years+.

Commercial solder mask is usually a photo process, but you can get other types that are for direct application. This one is in pen form for touchup use and would be too expensive for general coating: http://www.mgchemicals.com/products/4190gp.html If you don't have a local Fry's Electronics, I don't know where to get mask material in bulk. Sorry.

Hey! I just found this video describing the whole process of LPI solder masks!
http://training.ipc.org/demos/vt38s.htm (QuickTime video!)

Take care,
-Peter

[R.G.]

:lol:
R-E-S-P-C-T...  oh... sorry... I heard music
:lol:

Good build habits are really useful. And you're absolutely correct that unreliability is not something that you can tolerate on stage.

I worry a lot about reliability in my stuff, and try to point it out to the people here. I shudder at the thought of stepping out to do a solo and having my Maximo HyperBlaster clone in the Altoids tin box crumple up into a pancake. But there is a counter argument that the people most likely to build effects are the ones least likely to use them on stage, so there may be some middle ground.

Maybe we should start a thread about reliability in DIY pedals.

[Eric H]

Cool trick on the DIY roller tinning.

For hand tinning, a bottle of liquid flux makes things much easier and results in the use of less solder.

Just melt a thin coating of solder over all the traces and they're be protected for the next 100 years+.

I don't build enough to make the roller feasible --though I might try it some time, just because it sounds so ...cool

I use Peter's method, though I smear a thin coat of plumbers paste flux on instead of the liquid (Home Depot, baby).
This takes around two minutes, and (as noted) uses very little solder.

-Eric

[Peter Snowberg]

:shock:

I would advise not using plumber's flux under any circumstances.

Chemically, it's filled with zinc chloride which under heat decomposes into hydrochloric acid to provide the cleaning action. If you don't strip 100% of the flux residue and wash the board in a basic solution to remove 100% of the acid, the board is a ticking timebomb.

Rosin style flux is the only thing you should ever use in electronics.

Take care,
-Peter

[Eric H]

:shock:

I would advise not using plumber's flux under any circumstances.

That's what happens when I multi-task.
Correct.
The paste-flux I use IS rosin-flux --and I really don't remember where I got it.
I use plumber's flux as well (I'm a carpenter) and you are correct about not using it for electronics.

-Eric