DIY solder mask theory (And a big one, need helllllpppppp)

[Zben3129]

Okay, so heres the deal,

I personally hate solder bridges, but who doesn't. I ordered my first solder masked board and soldered it the other day. WOW what a difference! So, of course, next step was to come here and search for the DIY solder mask. Uh-oh, not possible. Gotta fix that


My theory is that we could, with losts of research, design some kind of solder mask they you apply pre-etching. It would either come before or after the etch resis, it would depend. The thing that makes this possible is that this would be a substance that somehow reacted with the pnp/ink, and is also etch resistant. Meaning that the stuff uncovered by etch resist would stay, and the stuff in contact with the etch resist would react chemically and combine with it. Or, maybe a physical reaction, though im not sure at what temperature ink / PNP melts... and I can't think of any other way to combine the two physically

Anyways, with the ink/pnp and solder mask combined, you could then just remove the two as one with the normal method of scraping/peeling/isopropynol/whatever you use and you are left with is clean copper traces and solder masked board elsewhere


In a perfect world 


Anyways, hopefully we can get this to come together, I would need lots of help though. If anyone would be interested in the design of this you can just leave a post or whatnot




© 2007, Zach B.


(Donno if the copyright is applicable, but what the hell it was fun typing it )

[Zben3129]

I've been thinking that this would be easier with press n peel because different inks vary in makeup and chemicals but pnp is (im assuming) fairly universal

[Paul Perry (Frostwave)]

I think there is a logic problem here.
Because, if you look closely at a solder masked board, you will see that some of the mask goes over the metal! except for around the holes, where you want to solder to...

So I think the only way would be to paint something over the entire board, that resists solder, and then use a drill of some kind to take off the mask over each pad around a hole.

[scaesic]

How about just etching a pcb as normal, then covering the board in wax?

You could just cover the pcb pads in some sort of wax resistant material first? There must be some artists out there?

[Zben3129]

yeah basically what I was thinking. But not having the traces covered is not a big problem for me. Im talking about the mask that helps prevent bridges. You can always cover the entire voard after with something to prevent oxidation

[scaesic]

i think having some kind of mask (selotape? or some kind of brittle paint that wax doesnt like?) on the pads and then dipping in wax or epoxy would be a good way to do it.

[Zben3129]

doesn't sound like a bad idea 

[Rodgre]

How's about this idea.

Etch your board. Clean it up with your usual methods (steel wool?) Then dab a small blob of white glue (Elmer's for example) on to each solder pad. A nice neat and round blob will look best.

Let it dry completely.

Now spray a nice and thin coat of paint onto the solder side of the board. Maybe a transparent color so you can see the traces clearly. Build up a couple of thin coats, just enough to cover the board clearly.

Once the paint is completely dry, wash the board in water. Lightly scrub the solder pads with your fingernails until the white glue dissolves. Bingo. A solder mask that looks clean and professional, and is only a mild p.i.t.a. to do.

© 2007 Roger Lavallee

[Zben3129]

That's a very good idea


Only thing is it takes a little bit more work, obviously, as you have to do each pad individually. Also, this would need to be done pre-drilling, as you wouldn't want to clog up the holes. And finally, need to make sure that the glue/adhesive does not leave any solder-resistive residue that could hamper the solder joints


Making some real progress 

[scaesic]

i like the water disolvable glue idea. What about investigating types of glue. i.e is there some kind of solvent you could dip the board into which would remove the glue and therefore removing the "scraping the glue off with your fingernails" stage?

I dont think theres going to be a way of doing this easily without applying some mask to the solder pads before you drill.

i was actually thinking that clear aerosol would be the easiest way to do it, maybe even transparent green/red for a more proffesional look?

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=TESR2501 enamal might be too hard though.

[Zben3129]

I think a thin coat is the way to go to start off. The thinner the better, as the thicker the mask gets, the thicker the layer on the glue is. You still want to make sure you dont adhere the glue dabs to the board, making them a royal PITA to remove

[Rodgre]

I think this is one of those things that is no big deal when you're mass producing a zillion boards to be assembled by robots in China, but for one-by-one projects, it's a p.i.t.a. and probably doesn't reap the rewards you'd wish for.

If we're coating the boards to prevent solder bridges, the real solution is just to be careful when soldering, not to mention when laying out your PC board designs. The other benefit of overcoating is that the copper won't tarnish and get dirty/contaminated over the years. I've seen circuit boards I made back in the 80's, which I got my oily fingerprints all over when I made the project, look all tarnished and dirty.

I thought that was why you'd see those E-H boards (and many others) from the 70's which were entirely flowed with solder, covering all the traces.

I still think that for the one-off DIY pedal maker who wants to invest the time into overcoating their boards like some professional boards are done, the white glue/transparent spray paint idea is probably the easiest, especially when you're talking about simple stompbox circuits with only a few dozen components.

The professional way to do it would be silkscreening. That's not impossible, and might be the best way to go if you're trying to repeat the mask over and over. It's also one of the best ways to do white printing on your stompbox, as well as legends on the parts side of your boards. Worth a try, if you're really obsessed with overcoating.

Roger

[PerroGrande]

Yeah -- I think the amount of time and effort spent to solder-mask a DIY board would probably be better spent fine-tuning one's soldering technique...

If you're making your own boards, you also have some degree of control of your solder pads and traces (apart, of course, from ICs, which dictate certain aspects of the spacing).  Some adjustments to pad locations and spacing might make soldering a bit easier.

[R.G.]

I'd like to second the "learn to solder better" sentiment.

There are some boards where I need solder mask; I recently had trouble unsoldering 0.032" pads on 0.05" centers and getting them clean enough to resolder without using solder wick braid. Anything bigger than that, solder mask is almost immaterial.

Solder mask matters A LOT to a machine that's never going to develop more skill though.

[bean]

Just fill your PnP image with black excluding the pads and transfer it to the trace side?

Or if you are using DIY layout then delete all the traces and leave the solder pads. With a little image manipulation in photoshop it would be easy to make a mask.


Ex. Delete all the traces in DIY Layout, export the pnp image. In PS, use the magic wand to select all the black color (the pads), expand the select a few pixels, smooth and fill with black. Now invert the entire image. That changes the pads to white. Print and transfer to the trace side of your PCB.

[soulsonic]

They sell that stuff in a spray can. It's called Conformal Coating, and they usually have it listed with the other chemicals and things that they sell for making circuit boards. I've never used it personally, but I think all you'd have to do is mask off all the solder pads with some tape and then just spray the stuff on there and peel the tape off. I've thought about getting some to spray on my boards after I've soldered everything to keep the copper from oxidizing and getting nasty.

[Zben3129]

thanks guys

Off topic, but where do you guys buy/get your etchant?

Thanks

[soulsonic]

I've gotten Sodium Persulfate from Small Bear, and I've gotten Ferric Chloride from Radio Shack. I've gotten good results with both, though I think I like the Sodium Persulfate better because it seems to be a "cleaner" process overall and it's not as nasty to handle as Ferric Chloride. You can usually find all the different chemicals at the different big supply houses as well like Mouser, Allied, Newark, etc...
I recommend purchasing from wherever is most convenient. If you have a local Radio Shack, you may as well try getting some Ferric there so you don't have to worry about hazardous materials shipping. I've never had any problems with stuff like that being shipped other than it usually takes longer because they have to ship it slowly - no airmail for nasty chemicals!

[darron]

are acrylic enamels satisfactory to do this? my laser engraver comes pretty soon and i'm going to use it to make all my diy circuit boards from now on. i figure it's only one more quick step and a few button pushes to make a soldering mask, so why wouldn't i?


and the colour of course has to be clear-blue

anybody know which sprays would work? the only conformal coating that i've been able to find is at RS components and i don't want to order just the one thing, plus it's really expensive...

adding to the (oldish) discussion, the soldering masks would be nice because:

1) protects from bridges

2) makes you lazy... (ermm. that's not good?)

3) protects your circuit from corrosion while still being able to change parts later. if you clear coat a circuit after its populated you need to avoid spraying everything else. and if you hit it with an iron later to change something you make a horrible mess as you burn your way through it. this way you'd spray it even before drilling and only the solderable areas are exposed, which should be covered with protective solder (:

[Jered]

  I'll 3rd the "learn to solder better" sentiment. Also make sure your using the proper equipment, new tips, proper wattage, .020 dia.(or less) solder, etc.
  Jered