[sdiy] For breadboard lovers...

[Ullrich Peter]

Hi!

>A vacuum pump!!, now that is a very good idea. It sounds like you are setup
>to build professional grade boards, Nice.

The vacuum pump is very essential! A thin plastic foil mounted in a frame come 
on top of your film-pcb-film stack and the air will be pumped out... So both 
films will be pressed onto the PCB.

But as the stack has to be laid on a glas plate of the exposure unit you need to 
have a PCB that is not bent, otherwise the film on the bottom side will not have 
direct contact to the photosensitive laquer on the PCB.

The DIY version of the exposure unit I had before I got the commercial version
Had no vacuum pump. I put a "plexiglas" plate on top of the PCB stack. Worked 
quite well but not as good as the vacuum pump.

Tip for double sided PCBs:

What you have to take care of when making doublesided PCB ist hat the top and 
bottom films match position. Pass marks can help here. But the most useful tip I
got from a collegue that worked with the unit for years was to use strips of PCBs for
film mounting.

So take a strip (maybe of an old PCB) with the same thickness as the PCB you 
want to etch and stick it to the bottom films (I take two film to get a good contrast).
The strip is here as a spacer so that the films don't have to be bent when the PCB 
is inserted between the film -so the film stay flat in the complete stack.
Then the top film can be glued onto the strip - mount the film on a light table so that
You can check the exact position. (You can build a light table easiliy on your own when
You take the backlight of old notebook or TFT displays...)

Another solution would be the use of a table with glas plate or work on a window...

But the big problem are the throughole connections. There is no really nice solution fort hat.
So I order more and more doublesided PCBs from a professional PCB maker...
So my setup is mostly used for single sided PCBs... Maybe some prototypes for doublesided PCBs.

Ciao
Peter