Homebrew PCBs

> PhilipP wrote:

> <snip>
> Apparently you can use UV LEDs to expose
> PCB photoresist - there was an  article
> in Elektor about it. They modified a
> plastic storage bin by adding a PCB with
> some UV LEDs to the bottom
> <snip>

UV tubes are still pretty cheap compared
to UV leads if you are going to make an
exposure box that is more than about 100
mm x 100mm.

> > I hope to make it cheap and easy enough for
> > anyone to make with mainly parts you could get
> > at places like Jaycar. (cheap and easy are
> > relative terms I know :D)
> 
> The hard part is going to be finding the
> steppers,

DC servo motor for drum.
Off the shelf stepper and a belt for the y axis
is the present plan

> and focussing the laser down enough to get a
> decent amount of resolution out of the film. I
> haven't seen any laser pointers that can be
> focussed down below 1mm...

I have found a supplier of lasers with focusing
optics that claim 10 or 12 uM and I will use
these for early prototypes.  However I would
like to do an easy to make modification to
common laser pointers with a bit of alfoil
for others to be able to make.

However even if I can't - the comercial 12uM
ones where sub $200 AUD.  Which is twice my
ideal BOM for the ENTIRE final unit - but
still bearable.

> <snip>
>> Red sensitive photoplotter film. It has
>> "dual sensitivity" at 635 and 680 nm I think.
>> Whatever the wavelengths are for common HeNe
>> and solid state lasers are.

> Where do you get that stuff from? I've never
> seen it for sale anywhere...

It's not real easy to get.

First you have to get some chalk and draw a
pentagram on the floor.  Next you have to
prepare the goat......

> How do you develop it anyway (in fact, do
> you need to develop it at all)?

Two step process like BW film for developing.

Develop then Fix.

The developer and fixer is specially designed
for the film.  The deamon that hands you the
blood filled pen when you get the film should
also be able to supply the developer/fixer.

> I did a bit of B&W photography a while ago,
> so I'm thinking of this from a "how is
> photoplotter film different to B&W film/paper
> emulsion" perspective...

Well - it's clear and black rather than white
and black.  It also has obscene contrast levels.
If you look at the sensitivity plots it is very
very non-linear.  Goes very rapidly from clear
to black with no grey shades in between.

The other difference is the lack of market
for it - so the suppliers can be as difficult
as they like and charge what ever price they
want.

Though with epson now making 4 shades of grey
ink jet printers I think that the market for
black and white paper is about to get about as
thin.

> > I think it works out something like $5-6 for
> > a sheet a bit bigger than A3 size.  I can't
> > quite remember exactly though - and I don't
> > have the details here.
> 
> So that's what, $2.50 an A4 sheet, or $1 for
> the average Eurocard sized PCB?
> 

I think so - I will have to check the prices
though.  Will get back to you all on the week-
end when I have checked.