[Robotgroup] Board etching experience/problem

[Gray Mack]

I built a board this weekend for a drum project using the photo etch process.
I have done this a dozen times before but things went a little differently this time so I thought I would
write it up since folks have been interested.
I usually use a good 600dpi laser printer or copier to produce the transparency, but finding a 24 hour copy shop these days is not as easy as it once was. Seems like they used to be all over the drag, but now tough luck, every body prints their own stuff I guess. So I went to Walmartz Saturday night and as expected they did have inkjet transparencies (the thermal kind dont like inkjet). 
 
These worked ok, but the ink was kind of light and took a good hour not touching anything for the ink to dry throughly. This is also convinient to print from home where I have Eagle cad running so the scale is correct rather than having to export to tiff and print at the exact resolution. To print from Eagle, I viewed only the bottom layer and the pads, then printed with the option (black) checked and the (mirror) option was unchecked I think. On the printout, the traces are black, spaces transparent and side with ink is inverted. The ink side goes against the board as if you were looking through the transparent board. You want to make sure that an IC will line up correctly with the holes as a sanity check.
 
I underexposed the light exposure time (~ 6 minutes) worrying about the ink being too light but it would have probably been fine to go a full 8 minutes.
Developing took longer than expected, to wash all the green off the copper to be etched, around 10 minutes. This was due to not being exposed long enough.
I didn’t have the transparency pressed super tightly to the board and a small part was a little fuzzy but usable.
I went over a few light traces with an etch resist marker.
Wear gloves for this and you can agitate with a foam brush.
I then rinsed the board to stop development.
I heated up my etching pyrex dish with hot water, then dumped the water and put in ferric-chloride. This helped warm the ferric-chloride a little bit which makes it work a little better.
 I etched for a few minutes until the yellow board was visible, agitating with a foam brush).
When it started to look good I washed it and studied it for cleanness.
If traces start to get under cut while other traces are still bridged then you can wash and selectively drip etchant on specific areas with the brush.
When it looked good enough I washed thoroughly.
I soldered it all together and parts of the board weren’t working. I was getting conductance all over the place and used a hobby knife to scratch between the IC pads but I was still getting weird readings. I was beginning to wonder if there was an invisible layer of copper still on the board. After checking all the traces 3 times I finally put the ohm-meter probes directly onto the board and was getting conductance!!! There is some copper in the groves of the board but I don’t think there are bridges. I noticed a shiny layer around a lot of the solder points. I thought it was just heat fusion or gassing residue of the solder (I recently switched to lead-free solder). This stuff is conductive! I have never had this problem before; I washed the board with water and scrubbed it with paper towel and cloth (difficult due to all the wires catching the cloth). This helped but there is still residue. I need to find some sort of circuit cleaner. I wonder if RShack still sells that
 tuner cleaner. Hopefully I can get all this gunk off without damaging the pots on the other side.
Has anyone else had this experience? Is it related to the lead-free solder? What cleaner is the best to use?
-Gray


       
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