[sdiy] PCB making: how to get a transparent foil with real black lines?

[Michael Buchstaller]

>Laser printing onto translucent tracing paper produces excellent results:

Sure. I do this all the time for several years now. Much better results than all my
earlier experiments with various types of foils.

But you have to make sure that the shop where you buy the paper does
give you one that is made for printing with laser/inkjet printers. Some of the other
paper sorts do not feed well through the printer.

>You *might* have to increase the exposure time a little to account for the
>attenuation, but a little experimentation will soon sort that out.

I use a 1000W film lanp with blue ("daylight") filter which reduces the light output
to approx 250W. Then i put a gray card (90 % gray) on the table where the PCB
will go later, and measure the light intensity with a light meter (settings: film speed
25 ASA, 1/60 sec. Exposure) and adjust the lamp height until the meter reada EV11.
Frome here, i have 6 mins of exposure to get perfect results with different brands
of photo-coated PCB material.

>There are plenty of pages on the web about using tracing paper, suggesting
>anywhere from thin 75gsm (crinkles in the printer, so have to flatten it
>first, but short exposure time) to thicker 120gsm paper (doesn't crinkle
>but longer exposure time).

i use 90g/m2


-Michael Buchstaller