Hi Rafael
would it be possible to use an 80W bulb insted ? Is just for the fact that I
already have the complete thing.
thanks
                Luis

-----Original Message-----
From: Rafael Fraga [mailto:rfraga@SY-NAPSIS.COM]
Sent: 22 November 2003 15:07
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]:PCB etching: gravity method works


To get the best exposure time, do a test:
Use a strip of sensitized board, cover almost all of it with something
non-transparent *to UV* light, and do an exposure longer than expected. As
the time goes, say each minute, uncover a little part of the board. At the
end, develop and process as usual. This way, you will get under and over
exposures in the same board, so if you took notes of the times, you will get
the optimum exposure.
I use a 500W mercury vapor lamp (standard lightning lamp), getting around 18
minutes at a distance of 20cm.
I use the gravity method, with saturated ferric chloride solution. As the
specific gravity of the solution is higher than the board, it floats easily.
Sadly, this is not so easy with ammonium perchlorate.
Photoresist:  Kontakt Chemie Positiv 20, positive action, spray applied and
oven cured.
Anyway, craftsmanship and luck are essential

Rafael Fraga


----- Original Message -----
From: Luis Moreira <Luis.Moreira@JET.EFDA.ORG>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, November 22, 2003 10:09 AM
Subject: Re: [EE]:PCB etching: gravity method works


> Hi Rick
> because I whant to try to do some PCB's for 44 pin PQFP to 208 pin PQFP,I
am
> not sure about exposure time and etching times, how would you solve this?
>                 Luis
>
> -----Original Message-----
> From: Rick C. [mailto:rixy@VVALLEY.COM]
> Sent: 22 November 2003 12:41
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]:PCB etching: gravity method works
>
>
> P.S. If you use a casserole dish, the bottom is not flat, but slightly
> rounded. Thus, the resist does not make contact with the glass. Only the
> very corners of the board touch the glass and leave enough etch solution
> to work on the board. Providing heat will circulate the etchant
> sufficiently. Occasionally, lifting the board and exposing it to air
> will also speed up the etching.
> Rick C.
>
> "Rick C." wrote:
>
> > You can etch and make lines as small as you can lay out the board.
> > Etching with copper side down will speed up your process as noted in
> > paragraph 6 on my website http://www.pic101.com/pcb
> >
> > Negative photoresist method I find is very successful with quality
> > results. However, my supplier of sensitized boards, Kepro, is out of
> > business so I'm back to sensitizing my own boards now.
> > Rick C.
> >
> > Luis Moreira wrote:
> >
> > > Jinx
> > > did you ever use the photoresist method ?
> > >
> > >   Luis
> > >
> > > -----
>
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