Limits of positive-resist circuit board making

[grunt]

For those who make circuit boards using positive mask lithography,
I have a fair assessment of how small one can make traces and details
on a printed circuit board.

The practical lower limit on the space between traces of copper is
twice the thickness of the copper. For 1 oz (per Sq.Ft.) copper at 1
mil, thats two thousandths of an inch.

The lower limit on the width of a trace is the thickness of the copper,
as above, one thousandth of an inch.

Masks can be made by reducing over-sized artwork to black and white
film (with a camera) from negative artwork.

Experiment with shutter speeds for maximum contrast.

In terms of application, one could fit up to 16 traces in the 20th of
an inch space between dip pads, etc.

- Geoff

 

[John Larkin]

On 13 Dec 2004 16:09:05 -0800, "grunt" <geoffreygallo@yahoo.com>
wrote:

For those who make circuit boards using positive mask lithography,
I have a fair assessment of how small one can make traces and details
on a printed circuit board.

The practical lower limit on the space between traces of copper is
twice the thickness of the copper. For 1 oz (per Sq.Ft.) copper at 1
mil, thats two thousandths of an inch.

The lower limit on the width of a trace is the thickness of the copper,
as above, one thousandth of an inch.

Few commercial board houses will do 4 mil resolution, and some won't
even do 6. 1 or 2 mil isn't practical on a board of any complexity...
yields would be too low.

Most board houses start with 1/2 oz or even 1/4 oz copperclad to get
the resolution, then plate it up. It's not uncommon these days to
order "1 oz" layers and get something less.

In terms of application, one could fit up to 16 traces in the 20th of
an inch space between dip pads, etc.

Functional traces on 3 mil centers? Not likely.

John

 

[grunt]

Ban Wrote;

You do not know what you are talking about. /snip/

Of course, you are absolutely right, I don't know what I'm talking
about. Follow this URL to a photo of the board I made yesterday with a
25 micron wire laying over the traces of the loop. Thats 0.001 inches
traces with 0.001 inches (25 micron) gap with 0.001 inches thick
copper. It's not pretty, but it is a functional field detector. Now
you can arbitrarily accuse the photo of not knowing what it's talking
about.
http://pg.photos.yahoo.com/ph/geoffreygallo/album?.dir=/e1ed

- Geoff