Tuesday, 26 November 2019

pcb - How long can room light shine on the board after exposure before board becomes useless?


For the positive photo-resist method of making circuit boards, I use UV blacklight to expose the board (with the artwork on it) for an hour, just so that I can make 100% sure its exposed properly.


Because the photo-resist layer on a circuit board is sensitive to light, what I like to know is, from the time I turn off the UV blacklight (to finish the exposure), how long can room light shine on the board before the board renders useless when it is being developed in a standard PCB developer solution?



or should I be super paranoid and work in a pitch-black environment starting from the moment the board is finished being exposed until I successfully predict the moment that the unwanted photo-resist is removed?


I ask this because I keep failing at making circuit boards from using the standard sodium hydroxide developer, and I'm looking into ordering sodium silicate, but until I get some, I'm trying to understand if working in pitch-dark settings actually makes a difference.


If not, then I'll ditch the sodium hydroxide and wait for sodium silicate.




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