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exposing double sided boards

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Simon:
So I'm nearly ready to take my first step in a double sided PCB project. Now my biggest worry is exposing the two sides correctly so that they line up. I've looked around the net but most guides are for toner transfer method. So how do I do it ?

I could tape the two artworks together and then put the blank board inside but as I can only expose 1 side at a time I may move the board in turning it over. I don't want to go cutting larger than needed boards for fixing purposes or damaging my artwork by keep taping boards to it as I may want to do a number of them.

There has to be a simple solution ??? well in the mean time off to search Utube

Mechatrommer:
i have this both photographic and toner transfer etching. the 1st time i used photographic, i directly put it back in the drawer (maybe for the rest of its life i guess). i use toner transfer thereafter. as you mentioned it, it is an "art" work.

Simon:
by artwork we generally mean the printout of the pcb onto tracing paper or inkjet transparency. There are projects that I'd like to make more than one of and for the price of the transparency I'm not using one copy per board.

Having looked at utube the solution was quickly revealed: yes make a pocket out of the two layers but then fix them with the board inside between two sheets of glass. So you can pick up the whole pack and flip it over, taping the two sheets of glass together will offer enough grip to stop the board sliding when it is turned over

Zero999:
I've never done double sided before but here's how I'd do it.

Cut the board to the required size. Make it as accurate as possible, using a file and a square as needs be. Pay attention to the datum sides, make sure they're the best.

On the artwork, put a mark on each corner which you'll use to line up with the artwork. Remove the protective film from one side, expose and develop, then do the other side.

Another thing you could try is printing the artwork for both sides next to each other, flipped and one PCB thickness apart so the paper can be folded round the PCB and secured with tape.

kaptain_zero:
I've never worked with photo sensitive pc boards before, but I've done a whole lot of work in a darkroom and these are things I used to do to 'register' multiple layers accurately.

The way I most often did it, was to use register pins. Drill two holes through the board at opposite corners (diagonally). Register the two 'negatives'  putting the same holes through them as in the board. Then you can use a couple of pins through those holes to line everything up together. Using 3 holes/pins makes it easier to line things up in full darkness if the third pin is placed in such a way that the 'neg' can only fit one way.

Another way is to use a board with a raise corner and two long side. Then cut the 'negatives' to the same exact size as the board and so they are properly registered. Then simply tuck the board into the corner with one 'neg' on top and expose, flip the board and place the second 'neg' on top and re-expose. This method is hard to do in pure darkness as things can get turned around the wrong way. My darkroom had a sodium vapor safelight that was bright enough to let me read a newspaper while still being completely safe for black/white papers I used for contact printing so I could see what I was doing. Working with color films/papers required full darkness, so pins were the only way to go. 

Using pins is generally more accurate and avoids having to carefully size each piece, and, if using 3 pins, can help avoid accidentally getting one of the layers turned around the wrong way in the dark.

I hope this makes sense....

Regards

Christian

PS: I see you found directions on how to use the board/sandwich method.....  The pins might be quicker by avoiding to have to accurately size all the parts.

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