Problem with positive pre-sensitized board exposure solved

[BobK]

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

 

[Harald Kapp]

Yellow is complementary to violett/ultraviolett and therefore blocks the high energy radiation effectively.

 

[HellasTechn]

First thing that poped into my mind before i finish reading your post was to get a new lamp