Pre-sensitized PCBs - What am I missing?

[Blues_Boy_4096]

Hi!

Here goes:

I made a box with 45 LEDs UV (400nm) to make the sensitization of the boards.
In an transparency, I printed, a test pattern, to test the some exposure times and to see which was most adequate.
I exposed the board, with different times of exposure for each "piece" of the plate.
Later, I dissolved a little of caustic soda in water, and dived the plate there.

This is were it started to go wrong....

The image appeared, almost instantly, but then dissolved in chemical preparation...

What it is that I did wrong?

I've already tested with two types of plates (a Bungard and other that I do not know the brand, bought from Banzai) and with different caustic soda/water concentrations and the result is always the same.

The image appears, and later PUFF! , it dissolves in the solution....

What am I missing?

       
   

[e45tg4t3]

thats the effect when to much soda is dissolved in water... try more water/less soda then it should work...

Benny

[Blues_Boy_4096]

thats the effect when to much soda is dissolved in water... try more water/less soda then it should work...

Benny

OK, but I have no idea of the proportions I should use.

Let's say, for about 10 ounces (250-300 ml) of water, how much soda should I add? 1 tea spoon, 1 soup spoon, more, less ??

BTW, a perhaps stupid question: The boards I've used are already lost for this, right? I can't sensitize them again.

Thanks

[e45tg4t3]

ca 5 gr. soda on 100ml water...  there is a way of sensitize pcb boards again... it a spray... in germany it´s called fotopositiv from solvent(the name of the manufactor).. but i don´t know if there´s something similar in the U.S. or somewhere else on the world...

Benny