Need assistance with positive resist pcb please

[LKO Railroad]

Hi. New user here. Kindly asking your assistance.

I have made many PCBs with MG Chemicals boards, developer, and etch. The results have always been pretty good. All of a sudden I am getting consistent failures. Nothing has changed in my process. I've tried fresh boards and developer but get same problem.

The boards come out of the developer looking as if they are overexposed. I tried stacking art screens, no difference. I exposed a board for half the normal amount of time and it reacted as you would expect - developing took much longer but ultimately got same result.

There are odd wave patterns across the boards and large areas of complete washout. My glass is flat and the board is sitting tight and flat against the art. When the art and board are viewed during exposing everything looks normal. The washout areas occur in random places and sizes from board to board. I normally use silk screen film which has always worked well. I tried a transparency but got same results.

For the life of me I can't find anything different from how I have always done this. Any clues?

(There is some residual water on this board. Very noticeable on the left. Sorry, I didn't dry it well before taking the picture.)

[jpanhalt]

That is puzzling.

I would try developing an unexposed board (or part of a board if you can cut it).   The resist should develop all blue-green.  If the color is not even, then it is most likely a bad board.  Like, light leaks during manufacturing or shipping.   Bad or poorly stirred developer might cause unevenness too, but I suspect you are using good developer, and your procedure has not changed.

John

[MrBungle]

Looking at those patterns I'd put money on bad resist. If it were me, I'd be going back to the manufacturer.

[LKO Railroad]

I developed an unexposed board. Same wave patterns and it too has washout area. Relieved to know my process isn't the problem. I'm going back to the supplier. Thanks for the suggestion guys.

[LKO Railroad]

I received new boards. They expose and develop correctly. Appears I had a bad batch of boards. It dawned on me the bad boards were delivered to my house on a brutally cold day. They sat in a box outside for probably 6-8 hours. I wonder if freeze thaw had something to do with it.

Regardless, I am back in the board making business.

[jpanhalt]

I suspect freeze thaw did nothing.   If the packages were not well sealed, irregular condensation of water could have occurred that might have done something.  Although, I doubt that was the cause either.

John