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Problem with positive pre-sensitized board exposure solved

Discussion in 'PCB Layout, Design and Manufacture' started by BobK, Dec 12, 2018.

  1. BobK

    BobK

    7,575
    1,633
    Jan 5, 2010
    I had been using the positive presensitized PCBs for a while, using a kit I got from MG Chemicals, which included what is basically an under kitchen counter fluorescent light for exposure in a light box I made. I was getting really good results with a 12 minute exposure. Then, after not using it for a while the same 12 minute exposure no longer worked. I thought the boards might have aged, so I got new ones with the same results. Thinking it was the fault of the inexpensive Chinese boards, I got some from MG chemicals. Same results. My exposure test showed that 30 minutes was now required. Changed the fluorescent tube. Same results.

    Then I noticed that the frosted plastic cover over the fluorescent tube was a bit yellowed. I took the cover off, and I now get good results with a 10 minute exposure.

    So, if you are using something similar and you want to decrease you exposure times, just remove the plastic cover from your light fixture.

    Bob
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,044
    1,813
    Nov 17, 2011
    Yellow is complementary to violett/ultraviolett and therefore blocks the high energy radiation effectively.
     
  3. HellasTechn

    HellasTechn

    1,403
    195
    Apr 14, 2013
    First thing that poped into my mind before i finish reading your post was to get a new lamp :p
     
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