The allure of double-sided boards

[Mark Hammer]

I'm pondering attempting a DIY double-sided board.  Not laying one out myself - I'm far too lazy and sloppy for that - but etching a known layout.

So, in preparation for taking that step, a couple of questions for you kids.

1) Let us say I covered one side of the double-sided copper board with a protective layer, like wide packing tape, then buffed the other side to a mirror-like shine and transfered the pattern for one side to it.  Then, let us say, after etching, I popped a couple of reference holes through the board, then masked off the etched side with tape, lifted off the initial tape and prepared the other side,lined up the resist pattern with the reference holes, transfered the pattern, and then etched that.

Does that strike you as a sensible, and relatively foolproof (considering there is a fool doing it) method for getting alignment between patterns?  Or would you recommend figuring out a way to line up the patterns and etch them both at once?

2) let us say that the person providing the layout also provides a legended parts layout.  could that parts layout be toner-transferred to an already etched board as if it were white paint, or does the toner absolutely need copper to leave its happy home and move?

[EATyourGuitar]

I've never done it but the white writting is either screen print or direct to screen printed on an expensive machine made for pcb's. I think when doing the iron on black transfers, you may have a problem getting anything to transfer where there is no copper only because it is a low spot.

[R.G.]

Does that strike you as a sensible, and relatively foolproof (considering there is a fool doing it) method for getting alignment between patterns?  Or would you recommend figuring out a way to line up the patterns and etch them both at once?

I'd very much recommend doing it one side at a time. Only I'd use spray lacquer for a resist on the side not being etched. Clean both sides; spray lacquer on one. Let dry (seconds). Toner transfer the copper side. Etch. Now strip the board in solvent, both sides. Lacquer spray the etched side, toner the all-copper side, and etch. Now strip both etched sides.

2) let us say that the person providing the layout also provides a legended parts layout.  could that parts layout be toner-transferred to an already etched board as if it were white paint, or does the toner absolutely need copper to leave its happy home and move?

Toner sticks to PCB stock better than it does to copper.

The true pain in the neck is the alignment.

[Gurner]

The other alternative.... 2 x 0.8mm single sided boards....etch some index crosses on them (obviously ensure the crosses are in the the same position on each of your individual PCB artwork!), drill the etched crosses out, use dowel pins  gluing them together (back to back...unetched sides), oh yeah.....use these things for 'through hole' vias .... http://uk.farnell.com/harwin/t1559f46/track-pin-0-84mm-pk500/dp/1143874 (ie drill your hole for a via, push the harwin pin stalk in in, snap off ...rinse repeat, solder 'em all ....job done).....everything will align.

[Mark Hammer]

Thanks, gents.  Encouraging and wise.

[R.G.]

The other alternative.... 2 x 0.8mm single sided boards....etch some index crosses on them (obviously ensure the crosses are in the the same position on each of your individual PCB artwork!), drill the etched crosses out, use dowel pins  gluing them together (back to back...unetched sides), oh yeah.....use these things for 'through hole' vias .... http://uk.farnell.com/harwin/t1559f46/track-pin-0-84mm-pk500/dp/1143874 (ie drill your hole for a via, push the harwin pin stalk in in, snap off ...rinse repeat, solder 'em all ....job done).....everything will align.

I like the two-boards approach too.  Same process, just you don't need lacquer.

[Joe Hart]

I like the two-boards approach too.  Same process, just you don't need lacquer.

And if you mess up one of them, you don't blow the whole thing, just half.
-Joe Hart

[G. Hoffman]

1) Let us say I covered one side of the double-sided copper board with a protective layer, like wide packing tape, then buffed the other side to a mirror-like shine and transfered the pattern for one side to it.  Then, let us say, after etching, I popped a couple of reference holes through the board, then masked off the etched side with tape, lifted off the initial tape and prepared the other side,lined up the resist pattern with the reference holes, transfered the pattern, and then etched that.

That's how I did it when I made THIS AMP.  On the two small boards, it wasn't too bad, but on the long preamp/PI board, the alignment slipped a bit.  Not so much that it wouldn't work, but a bit.  Still, on a small board, you should be fine.  I'm about to do another amp with similar boards, and because I've moved up to photo resist, I'm going to do it with two single-sided boards instead of one double sided.  (In fact, I'm probably going to etch those tonight.)  The only problem with this is that now I'm left with a bunch of 2 oz. double sided 1/8" board that I have no immediate use for.  But I'll figure out something.

Oh, and I do like a good heavy duty packing tape for a quick, not too precise resist.


Gabriel

[bean]

I've gotten very accurate double sided etches from using index markers only. To align, I use the old fashion method of drilling the four corner marks, poking the transfer material with a needle and then lining them up using a light shining directly at the board. It's not all that hard, but also not something I would do unless I really had to!

[smallbearelec]

I just posted a really good candidate:

http://www.smallbearelec.com/Detail.bok?no=247

SD

[RedHouse]

I'm pondering attempting a DIY double-sided board.  Not laying one out myself - I'm far too lazy and sloppy for that - but etching a known layout.

So, in preparation for taking that step, a couple of questions for you kids.

1) Let us say I covered one side of the double-sided copper board with a protective layer, like wide packing tape, then buffed the other side to a mirror-like shine and transfered the pattern for one side to it.  Then, let us say, after etching, I popped a couple of reference holes through the board, then masked off the etched side with tape, lifted off the initial tape and prepared the other side,lined up the resist pattern with the reference holes, transfered the pattern, and then etched that.

Does that strike you as a sensible, and relatively foolproof (considering there is a fool doing it) method for getting alignment between patterns?  Or would you recommend figuring out a way to line up the patterns and etch them both at once?

2) let us say that the person providing the layout also provides a legended parts layout.  could that parts layout be toner-transferred to an already etched board as if it were white paint, or does the toner absolutely need copper to leave its happy home and move?

Check out these guys:  http://www.pcbfx.com/main_site/pages/start_here/overview.html

[John Lyons]

Here's what I have done:
Double sided copper clad
Print out both sides of layout (top bottom)
to your favorite transfer medium (photo/magazine...)

Sandwich both side together (toner to toner) up against a bright
window or glass and bright light to register them. Tape edges at
right and left of board creating a pouch with top and bottom
open.
Prep and slide in your board. Tack and iron both sides as usual.
Tada!

[G. Hoffman]

I'm just about finished with the two sides for the amp I'm working on (I really did do it tonight!), and I think I like this way of doing it.  Now, this is going to be using eyelets and turrets in a lot of places, and the top side board is really just a ground plane - no actual traces between the pads - but the photo etching process is accurate enough that it really does line up, even on a 10"X3" board like the one I'm working on.  I lined it up using two opposite corner stand off holes, and every thing lined up well enough that I can't see any error.  Very nice, that.  I used a couple of machine screws to bolt the two boards together, and I drilled the rest of the holes in both boards at the same time.  Very nice.  I've still got to cut them to size, but that is easy enough to do, and then it's just staking all the turrets.


Gabriel

[egasimus]

Here's what I have done:
Double sided copper clad
Print out both sides of layout (top bottom)
to your favorite transfer medium (photo/magazine...)

Sandwich both side together (toner to toner) up against a bright
window or glass and bright light to register them. Tape edges at
right and left of board creating a pouch with top and bottom
open.
Prep and slide in your board. Tack and iron both sides as usual.
Tada!

Pure genius. You're the man! I'll try that.

[Mark Hammer]

The other alternative.... 2 x 0.8mm single sided boards....etch some index crosses on them (obviously ensure the crosses are in the the same position on each of your individual PCB artwork!), drill the etched crosses out, use dowel pins  gluing them together (back to back...unetched sides), oh yeah.....use these things for 'through hole' vias .... http://uk.farnell.com/harwin/t1559f46/track-pin-0-84mm-pk500/dp/1143874 (ie drill your hole for a via, push the harwin pin stalk in in, snap off ...rinse repeat, solder 'em all ....job done).....everything will align.

I like the two-boards approach too.  Same process, just you don't need lacquer.

But what does one do about ICs?  Do you use wire-wrap sockets to make sure the pins go all the way through?

[R.G.]

But what does one do about ICs?  Do you use wire-wrap sockets to make sure the pins go all the way through?

One gets thin material. PCB stock for multilayer boards is half - or less - of the thickness of normal 1/16" / 0.062" / 1.6mm board stock.

But yes, if you can't get thin stock for the two-board version, one uses long pins so you can solder both sides.

[Gurner]

The other alternative.... 2 x 0.8mm single sided boards....etch some index crosses on them (obviously ensure the crosses are in the the same position on each of your individual PCB artwork!), drill the etched crosses out, use dowel pins  gluing them together (back to back...unetched sides), oh yeah.....use these things for 'through hole' vias .... http://uk.farnell.com/harwin/t1559f46/track-pin-0-84mm-pk500/dp/1143874 (ie drill your hole for a via, push the harwin pin stalk in in, snap off ...rinse repeat, solder 'em all ....job done).....everything will align.

I like the two-boards approach too.  Same process, just you don't need lacquer.

But what does one do about ICs?  Do you use wire-wrap sockets to make sure the pins go all the way through?

The two boards I used are half the thickness of typical (1.6mm) PCB board & measure in at just 0.8mm thickness. (easy to source here in the Uk, not sure what that is in yank 'base 32' type measuring systems!)...when they're joined they form a board measuring 1.6mm thick ...which is the normal thickness of a PCB board....so no worries about IC pins being too short.

[boogietone]

If one of the boards was double sided, is it possible to use one of the sides as an interior ground plane, or is that asking for too much trouble? Would it even be useful?

[Gurner]

If one of the boards was double sided, is it possible to use one of the sides as an interior ground plane, or is that asking for too much trouble? Would it even be useful?

Do-able I guess (if you gave each one of your through holes a wide birth by the copper blane), but that makes each one of your though hole parts & vias a possible potential short to ground!

[MikeH]

I'd be interested to know how this works out for you; I tried a couple of years ago and FAILED miserably.  Although I was trying to do a really big board.  It think it would have been a lot easier if I had some double sided clad that was clear.  But usually it's green or baby-poop brown.