PCB Transfers for double sided copper clad

[boyersdad]

Hey gang!

Just wondering if anyone has any experience with etching double sided boards?

I've got a transfer for a "Week Joe" compressor - something like a tricked out Joe Meek comp. It's a double sided layout.
It can be built as a single sided, as the bottom layer is used solely as a ground plain, but that would introduce a bunch of headache getting to ground in some spots.
Plus, a big ground plane is good for RFI rejection etc etc.

Anyway, from a practical standpoint, I'm not sure how I'll execute this.

My regular workflow for single sided boards is as follows:
I use a laser printer, to PnP (or sometimes magazine pages), sand/clean PCB, pre-heat board with hand iron, apply PnP transfer, cover with sheet of paper, iron for 2 mins, etch in ferric chloride, quench under water, peel.

What would the work flow be for a double sided board?

I was thinking I could print both the top and bottom transfer separately, cut them to shape/size, line them up back to back, and stick a map pin through each of the corners. Then I'll drill a hole through the copper clad using one of the transfers as a template. Then I'll stick a toothpick, or maybe something nylon, through one of the transfers and the hole in the CC. Then, I can slide the second transfer over the "stakes" coming through the other side of the CC, creating a PnP/copperclad/PnP sandwich (delicious!).

Then, I could put one on, line it up, iron it, flip it, iron on the second.

I'm just worried about the transfer bleeding off of the first while I iron the second.

Anyone have any better ideas?

Thanks!
Sean

[frank_p]

Here are some tips from John:
http://www.diystompboxes.com/smfforum/index.php?topic=78081.msg642339#msg642339

[John Lyons]

You beat me to it. 
Boyersdad, can you share the schematic for that one?
I'd heard of it but not sure I've seen the schematic.

Thanks

John

[Naz Nomad]

http://www.geocities.com/m_natsume/what_compressor.html

[newperson]

I have tried the pin idea before and it does not work 100%.  The best and easiest thing that I have found it just to line the 2 pnp blue sheets up and tape them together and then slide your copper board between them.  This works almost perfect ever time.

[John Lyons]

So basically the same thing as the link above  

Thanks for the linky Naz!

[newperson]

I guessed the link was the same information but did not follow it.  I had a question for you John.  Do you etch with acid or by electrolytic?  And if by electrolytic etching do you have any tips? 

[John Lyons]

The Electrolytic methode will mot etch PCBs because if you have a freestanding pad there will be no way to
attach an electrode to it. Once you etch through the copper you get to a point where you
can etch no more as they will be no connectivity between the wanted and unwanted copper areas?
See what I mean?
You can do this method if you design the board to work with it (traces left to keep the process "connected")
but then you have to cut them off afterwards. Which will not work will all the pre made layouts.

By the way...I use muratic acid and Peroxide.


John

[newperson]

Thanks for the info.  I have been reading about electrolytic but I have not seen anything about Pcbs.  I guess this is why.  Do you like muratic better than ferric?  Does it etch quicker?  I have been using ferric with a heater and it is about 30mins for a board. 

[boyersdad]

Thanks for the tips fellas!

Yes, that's the correct address for the documents I'll be working from.

On that site there's an audio sample of a mix the creator of the Weak Joe used on a remix of a song.
It's unclear whether he used the compressor across the stereo buss, or whether he used it on discreet tracks, or both...

His remixed version compared to the original mix is definitely squeezed, but it doesn't sound all gross, like if you had have used an Alesis for example. It still sounds nice, and I guess that's supposed to be one of the main selling points on this design.

Can't wait to build it up!

Thanks again guys!

[John Lyons]

Sorry for the off topic...

Newperson.
I can etch a board in a few minutes or so with fresh muratic/peroxide.
It's clear also so you can see what's going on.
Many posts about this here so search away!

John

[ricothetroll]

hi !

yesterday I etched a double sided board using the following method :

- buy some 0.8mm presentitized PCB
ex : http://uk.farnell.com/cif/aab20/pcb-presensitsd-epoxy-1f-200x300/dp/1267745?Ntt=1267745

- etch both sides (with Eagle for ex, bottom side normal, to side mirrored)

- drill 2 corresponding pads, one at each corner, and solder a piece on solid wire on one side

- put those two wires in the corresponding drilling on the other side and solder them while maintaining both sides tight. now both sides should be aligned correcly.

- solder a few more pads if you have a big circuit, to make sure both sides are stuck together correctly.

- drill you board. if you did a good job at previous steps, every top hole must be aligned with the bottom ones.

that's it ! just don't forget that there's no through hole plating, so components must be soldered at both sides to make a good top/bottom connection. If the pieces of wire aren't placed at vias, you'll have to desolder them and put the corresponding components instead. But don't forget that when the board is still empty, they are the only "glue"  to keep both sides together ! do them in the end.

That's kinda stupid method, but it works and alignment is a lot easier than working with "real" dual sided pcbs.

hope this helps.

best regards.

eric

[Gurner]

I had to read that a few times...but you're essentially combining 2 x 0.8mm boards to make one 1.6mm board?

I'm about to have a pop at a double sided board myself. but my attack will be slightly different (I'll be using one 0.8mm presensitized double sided board)....

1. Put some index marks on your pcb in Eagle - towards the edges of your PCB & at  diametrically opposite corners

2. Find some convenient very flat material ...a bit larger than your intended pcb (I use acrylic cos it's nice to work with & very *very* flat) - place a printout of your PCB design on top of it - tape it down & centre punch the index marks of your PCB printout  through onto this material

3. Drill the index marks with a 2mm drill (or 3mm drill - infact whatever you have to hand & depending how small your pcb is)

4. Bow place some 2mm steel pins into the 2mm hole (pins should be smallish in length - about 8mm is ideal)

Ok, so now you've your 'exposure bed' ready!

5. Now take your double sided pcb, don't remove the protective plastic - place your PCB printout over it again - centre punch the holes (make sure the pcb paper doesn't move!)

6. Drill out the punched holes on your unexposed PCB board with a 2.2mm drill (this gives a slight bit of room for punch/drill alignment errors)

The unexposed pcb should now slide fit down over the pins & sonto the exposure bed prepared in steps 1-4 above.

Now all you need to do is print out your pcb, punch out the two holes on your 'medium' (acetate, tracing paper etc) where the index marks are - you need to get the orientations right - but everything will align up now

The above is more likely to be worth doing if you've a few board to make.

A couple of thoughts....

use some waste pcb material to create a frame around your pcb (to stop light bleeding through underneath when the second side is being exposed..
Don't cut your pcb material too fine near the edges ot you'll get UV light bleeding through underneath onto your wanted traces while exposing the second side
make sure your vias are placed through at points with large tracks (to avoid aligment problems)

you will need 'press down' glass cut to size so that fits in between the pins - even better if you can get the glass drilled where the index marks are - but say 4mm holes (though I appreciate for most this is gonna be hard to do!)

Use these handy links for vias to 'join' the two sides...

http://uk.farnell.com/harwin/t1559f46/track-pin-0-84mm-pk500/dp/1143874?Ntt=114-3874 - push into the via hole (they're tapered), snap off, solder both side - job done!