Homebrew PCBs

I'll assume you're using the cheap readily available negative exposure 
dry film.

As others have said, 15 seconds, sounds too short.  I use about 2m30s 
with doubled tracing paper and UV leds, I think last time I used the sun 
(too big a board for my box) I put it out for about 5 minutes.

You should be using Washing Soda (Sodium Carbonate) to develop somewhere 
in the region of 20g/Litre - 5 minutes and a bit of a rub.  In fact I 
use it to strip as well (just warm up a stronger solution for stripping, 
soak 1/2 an hour, and the resist will float away), it takes longer but 
it's safer in all respects. Sodium Carbonate is available at your 
nearest supermarket, look in the laundry aisle for "natural" products, 
read the label, there'll be one there that is probably 100% Sodium 
Carbonate for sure.

For hobbiest purposes, there is piles of lee-way with long exposures, if 
your artwork is sufficiently high contrast.  When exposed, the traces 
are clearly visible.  I'd suggest doing some small test pieces 
(something that has traces about as thin and closely spaced as you would 
want to use, like a SO16 breakout or something) to see how long an 
exposure you can get away with before you start seeing trouble.  You're 
a hobbiest right so no need to be crazy precise, mark-one-eyeball it.  
Start with say 3 minutes, if it looks too-far-gone, try the next one 2 
minutes, if it looks ok, try one at 4 minutes.  I think you'll be 
surprised just how long an exposure you can "get away with".

Also, try using the doubled-tracing paper artwork.  Way cheaper than 
acetate.



On 13/05/13 02:07, dave_donlan wrote:
>
> Hi guys
> I am using UV exposure method on clear acetate
>
> 15 secs exposure caustic soda developer about a 60 secs
>
> hydrochloric acid / peroxide etchant no bubbler just sloshing about 
> but the problem is the protective layer is coming off after a few 
> minuets of etching
>
> hydrochloric is 30%
> peroxide is 9%
>



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