Double sided DIY PCB's..a solution?

[Blueteeth]

Hi,

Well, I have finally got round to making my first double sided PCB using press'n'peel paper, its a small USB blaster clone, 2 x 1". I have read about aligning the p'n'p sheets, and taping them together to form a 'pocket', then sliding the substrate inside, and ironing. I did it by having two alignment holes on the top and bottom prints, and drilling through the PCB, then stapling both designs onto the PCB through thoses holes. No perfect, but not bad. All my vias lined up well enough.

Whilst I was doing it, I suddenly realised it would probably be far easier to simply etch two single sided boards, drill a couple of holes in them for alignment, then glue them together with epoxy, before drilling the rest. With 0.8mm (1/32") thickness board it should end up as standard 1.6mm thickness. Alignment should be pretty much perfect, since they are aligned 'after' etching using the existing drilled pads for alignment. A couple of vero pins, some epoxy and a vice/press, and it should work out.

It may sound like a lot of work, but dealing with 0.8mm board has its advantages, cutting/milling becomes a whole lot easier for a start.

I just wondered if anyone has done this before? of course there are no plated through holes (made my own copperset bails for that) but I have perfected the p'n'p method for 0.5mm pitch IC's so I'm looking for more ways to improve things.

Blueteeth.

 

[BeeBop]

Hi Blueteeth,
I didn't find the 'pocket method' worked very well for me. I did have success with drilling a hole in each corner after etching the first side, and using wire pins to align the placement of the second side resist.

I also had some success with the second method you mention, but I used 1/64" board (also nice because it can be cut with common kitchen sheers.)
The problem with that way was that if the holes are not aligned perfectly the board can warp a bit.

I'm curious what you mean by 'copperset bails.' Could you amplify this a bit?

 

[Boncuk]

Hi,

the pocket method works well if you use film. Not being able to look through the printed paper it is almost impossible to properly align both sheets.

Furthermore - this applies to big size boards (≤420mm length) - the prints are never the same scale.

Making a pocket requires highly precise work. I usually use strips of the same PCB material thickness as the one intended to etch and make a U-shaped frame with one film taped to bottom of the strips. Then I use double sided adhesive tape to fix the top film on the frame. The PCB has to fit snug into the pocket so it won't slip to either side when turning over the assemly for exposure.

Best method to align both films is using a light table and poke small holes in the reference pads to align the films diagonally, poking the holes absolutely vertically.

Boncuk

 

[DirtyLude]

I don't know, this isn't all that complicated for me. I use the 'pocket' method, but I only tape two sides.

I use regular photo paper and I use a lightbulb to see through both pages. I usually keep my dimensions line on the print, which is a thin line all around the board; with lining up the via's as well, I can get it very well lined up.

I tape the two sides and place the board in it. Iron one side, then flip it and iron the other. I haven't found any need to 'pin' it to the board before ironing.

 

[3v0]

You can etch one side at a time. Use box tape to mask off the side you are not etching. Use a PCB about 1 inch larger then required and center your artwork. This allows the etchant to creep under the tape a bit.

I CNC drill the PCB prior to etching. The etchant does not bother the copper on the masked side of the board.

Not all brands of box tape work equally well. I found a no name tape that works better then 3M.

 

[Chippie]

@ DirtyLude, nice looking boards you made there..


The only double sided board I ever made was for an eeprom programmer for my BBC microcomputer back in the eighties...

I blanked one side with cellulose paint ot protect from etchant, laid out the other side using rub down transfers etched it, drilled it, then painted that side while I worked on the other...boy what a lot of effort...but we didnt have UV board or Press'n'Peel in those days...