Re: PCB Etching (Was : Phono Faceplate - Photos)

[James Derrick <james@xxxxxxx>]

On Fri, 17 Nov 2000 13:58:06 -0000, you wrote:

>I use photo etching.
Same here, except for hacked together _definitely_ one off boards.

>My biggest problem at the moment is lack of a Laser Printer although
this
Hmm. I tried laser printers, photocopiers, etc a few years ago.
Photocopiers were the worst as when the tracks were densely black
enough, there tended to be shadows elsewhere. Laser printers were not
bad, however it was easy to damage (scrape) the toner off the master
especially if you put the board on the toner side of the master.

I found a HP DeskJep 660c with HP transparencies gave the darkest
master with the best contract. HP film looks rough on the ink side
(like it's been sanded) and takes ink very well. The black is _very_
black.

>My inkjet printer gives less than perfect results. The image is clear
but
>the black is nowhere near dense enough. This means I have to be
EXTREMELY
>careful with the exposure times or I remove all the photoresist :-(
Hmm. Could it be the film is not the best type for your printer? The
HP stuff I use is more expensive than alternatives, but works.

I did try polyester draughting film as this takes ink well, but is
opaque.

>If you do opt for the Photo etch method BUY THE PRE-SENSITISED BOARDS.
This is something I did wrong for years. Again, quality costs!

Maplin pre-sensisised board was very hard to work with, but the
aerosol spray was damn-near impossible to use. The thickness of
coating is just too hard to get even.

I switched to Farnell board, and lo and behold, the same masters and
chemicals gave perfect results. This board was a lot more forgiving
with UV exposure, with a wider range of exposures giving good results.

Fine tracks became possible to etch- previously these were
over-exposed out. One tip is to make a test master with a mixture of
track widths, and try it with a range of exposure times. This makes
judging underexposure (copper left), or overexposure (thin lines
disappear) much easier and scientific.

One other pitfall- I made my UV light box from scratch, getting UV
tubes from a general supplier. It appears the light from some tubes is
not 'hard' enough (power? frequency?) for PCB exposure and my boards
were disappointing. In desperation I splashed out on expensive PCB
light box tubes, and again the results improved.

>I did invest in a bubble etch tank last year along with aquarium pump
and
>the results are amazing. The quickest etch times ever with all areas of
the
>board evenly etched.
Never tried aeration, however I warm the ferric sulphide in a sink of
hot water then float the board on the top using surface tension. This
reduces the chance of one portion etching faster than another as
removed copper salts fall with gravity.

>You do need to cover anything in a 1 metre radius with old newspaper
though
>because the little bubbles pop and spash ferric chloride everywhere.
Just 1m? ;)

When no one is looking, work in the bottom of the bath. That way,
splashes can be washed off the tiles and bath sides. The plug hole
does suffer though!

>Remember, EYESHIELDS, GLOVES, VENTILATION.
Also get a cotton lab coat to protect your body- mine has lots of
chemical burn holes and is rusty brown with the iron salts!

TTFN,

James
---
James Derrick    james@xxxxxxx, Cramlington, Near Newcastle, England
Forwarding Service: jderrick@xxxxxxx
Beyond the Horizon of the place we lived when we were young,
In a World of Magnets and Miracles. Pink Floyd.

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