The allure of double-sided boards

[rrroo]

are there any good available dual layer projects? ive got some dual pcb:s and all the tools but can't find any ready projects. my time is too limited to start designing my own pcb layouts... of course i could do just single sided pcb:s but i've got the duals for free.

[R.G.]

Nobody makes (DIY that is) them, so nobody lays them out for DIYers. It's the classic chicken-and-egg problem.

[frank_p]

If you really want to do it.  Search for John Lyons posts.  He had a simple method for etching the boards.  But keep in mind that it may be complicated for not much gain.  It's a precision job.

[rrroo]

the etching is not a problem. the problem is: what to etch?

[greaser_au]

The true pain in the neck is the alignment.

When I was still at high school, over 30 years ago!- I used to make PCBs at home. Patterns were designed on paper, it's holes poked with pins, the pattern was then taped on to the copper and a dot of ink put through the pinholes in the paper pattern.  The resist pattern was manually applied to the copper (using the dots as references) using adhesive layout tapes (kit included strips of various width linear tracks, pads of a few diameters,  rows of DIL IC pads - super easy!!),  and a resist pen  (or a permanent texta (~= sharpie)). I  bought all this stuff in a little kit with some board material and a bottle of FeCl from Tandy (Radio Shack) - even the board material in the kit was fibreglass

I used to make my own DS boards-  one side at a time - too. starting with some DS phenolic board strips I was given by my teacher (thanks Mr Wynne!!!), I  carefully applied PVC electrical tape on the non-etch side.  and laid out the bottomside pattern. When I had etched that side,  I'd drill a few holes for alignment (registration), sight it against a light through the topside  pattern, tape it down, ink the dots,  lay out the unetched side , pvc tape the etched side and etch again. As for the vias. I'd solder the components on both sides,  and where necessary add a few top-to-bottom links). The first thing I made like this was a double effect bypass switch, with a 4013 and a couple of 4066's- pretty easy, one just had to be patient and meticulous.   As R.G. says,  the hardest bit was accuracy in the alignment of the top & the bottom patterns.  If I was doing it now in single quantities, I'd still likely use the 'drill a few holes' method.

As for using toner as legending - I know some black toners use carbon black - might make for some random resistors here and there  I don't know about the CMY toners used in colour printers-  they became  common after my time on the road (sometimes) fixing laser printers!

good luck!!!
david

[CodeMonk]

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.

I like your idea with the lacquer there.

As for alignment, here is a tonebender (with a tweaked BMP  tonestack, board mounted pots, and switch)  I did on double sided.
This particular layout I haven't verified yet though.



The dark traces are the normal trace side, the lighter colors are traces on the component side.
The big pads outside the board area are what I use to align with.
I do a thermal transfer on the normal trace side, then drill out the holes on the large outer pads.
The size of the drilled holes are sized for round wooden toothpicks, which I use to help line things up.
Then transfer the other side and etch it all at once.
I've done about 40 boards this way and only had to scrap one (the bad one was about twice the size of this one).