I have a positiveresist PCB that I exposed the board to UV to transfer a layout for 5 min. I use UV box that I bought from Mega UK.
After that I put the board onto positive developer. As I did not have a measuring cup, I used a small cup to obtain NaOH to water ratio 1:10 (the datasheet says 20 gr onto 2 liter). Then I put the PCB onto the solution (temp. around 30 C as datasheet says) and waited some time, then it solved all photoresist film including the layout, then I thought maybe the solution was too strong and added more water (the ratio should be 1:20) then put a new board onto the solution, I saw the layout of the board in 15-20 sec then I removed the board and put it under a cold tap water, then the all layout washed away and I had a blank board.
Can you tell what I am doing wrong and how can I understand when to remove the board from the solvent?