Etching multiple boards at the same time

[z7yh]

Hello,
I arranged a bunch of pcb layouts with photoshop so I could print print it to a full sheet of PNP blue, then transfer them to a sheet of fr4 without cutting it up, then etch it and cut it up afterwards. Will this work or will I have problems getting a good transfer with a whole sheet? If it won't work what would be the best way to do this? I want to etch a bunch at the same time, and waste as little PNP and FR4 as possible.
Thanks Dave

[sta63bmx]

I like the idea of printing everything onto one sheet of PNP at once to maximize its use.  But I don't think it will be possible to use a regular iron to transfer that WHOLE SHEET to the copper-clad board at once with a household iron.  If you go to a place that does vinyl lettering, they should have a mangle press that's big enough to do it, but it still might be too much area to really work.  I would just cut the small pieces of board and iron them individually.  If you cut after you iron the stuff on, you run the possibility of accidentally scratching off traces.  If you etch the whole sheet at once, it might start eating the outside while the center is still etching.  But if you COULD etch the whole piece at once, you'd still have to cut and might ruin traces.  I just do the small boards individually and throw them all in the pot to etch.  I'm only etching 3-4 at a time, though.

Good luck!  If you try that mangle press, let us know how it turns out.  We had one in our sporting goods store and I wish I had access to it now.

[z7yh]

If I cut up the PNP after its printed wont the toner get rubbed off?

[Mark Hammer]

Etches usually come out better under noncommercial etching circumstances when the board is facing down.  That way the molecules of copper chloride or whatever you get as a byproduct of etching sinks to the bottom of the container/tank.  The risk created, though, is that when the board is placed in the etching tank it will either sink to the bottom or, if it floats, get air bubbles trapped underneath.  Obviously if the board is large, the likelihood of trapping air bubbles when you try and float the board is increased.  One solution is to do what I've done with success in the past, and thatis to drill little holes in each corner of the board and insert toothpicks to make the board like a little table.  That way you can keep it below the surface but it won't sink.  Ideally the board would be placed into the etchant bath in a way that any air bubbles would escape.

The more pressing concern, however, is that unless you have a reasonable sized tank, with a bubbler, it will be hard to assure that the etch proceeds uniformly, and that can pose problems.  We often think of the etch proceeding vertically.  That is, it etches from the surface down to the bare fibreglass/phenolic.  But the etch also proceeds horizontally, from the outside of the trace (which is not covered with any resist material) inward.  If one part of the board is taking dramatically longer to etch than another, then the etchant can be gnawing away at the sides of the traces over here, while you are still waiting for it to work its way down to the bare phenolic over there.  Obviously, this is not an issue for big commercial PCB houses that regularly churn out tens of thousands of computer and TV motherboards well in excess of 8-1/2" x 11".  But it CAN be an issue for people like us that make a board here and there in a tupperware container.

This is the long way of saying that even if you could successfully transfer the whole pattern to a big piece of copper board, the smart thing for etching purposes may be to have as small a board size/unit as you can to assure the most uniform etching possible.  Certainly, something that had a couple of layouts might not be that problematic (e.g., I had a board with a half dozen circuits that was about 4" x 4" and it etched without problem), but a very large board might be.

The other thing is that when trying to stuff many layouts onto one PnP sheet (it IS expensive, isn't it?), we can often end up with blank spots required in order to be able to orient this layout this way so it will juuuuuussssssst fit.  When the entire copper board is etched at once that can result in vast expanses of copper being exposed, using up the etchant bath that much sooner.  Far better to work with small controllable sections, where you can take you Sharpie pen or nail polish and cover up the unused corners and such so they stay coper and can be used as grounds.

[z7yh]

So would the best way to do this be to print it on paper, use that as a map to cut the copper, then print the PNP, carefully cut it up, and transfer them one at a time. If that would work how many should I etch at once?

[Mark Hammer]

Personally, I print out the layouts, cut them to the minimum possible size, spend 5 minutes figuring out how to fit as many as possible on a single 8-1/2 x 11 sheet, tape them down, photocopy that sheet to paper a couple of times until I get the toner darkness just right, and then photocopy to PnP.  Once the PnP is printed, I cut the layouts out with scissors and store them in an envelope for later use, whether one or more than one at a time.

[z7yh]

How long is the printed PNP ok to store?

[Mark Hammer]

Years and years.  Just make sure you store it flat.

[z7yh]

ok Ill do it that way. Thanks

[Pushtone]

I do what you are asking but with the 4" x 6" copper clad
boards from Small Bear so it's a manageable size.

This is what I do...
1. Combine layouts in Photoshop,
2. Laser print onto paper
3. Tape a piece of PnP Blue over the printed page as per Tonepads photo essay instructions.
4. Laser print onto the PnP.
5. Iron the PnP onto the copper (after prepping the copper as per Tonepad instructions of course)
6. Use a utility knife and strait-edge to score and snap the layouts apart. (eliminates harmful glass dust over sawing PCBs apart)
7. Etch the individual boards. I do four or five at a time in a Tupperware tub with hand agitation.

It's OK to leave the PnP on the traces until your ready to populate the board. How long? A long, long time.
See my thread on wet drilling the PCBs too. Bit of a debate going on there too.
http://www.diystompboxes.com/smfforum/index.php?topic=44440.0