Q: cutting presensitized PCBs to size

[burningman]

Does anyone see any issues with cutting presensitized boards to size, before etching?

[fpaul]

I cut them slightly oversize with tin snips and then trim them after etching. Oversize so if some of the resist is damaged I have some wiggle room.

[burningman]

The reason I am asking about trimming to size before etch is because I am testing exposure and developing times and don't want to waste an entire board. I just wanted to make sure that cutting the presensitized boards to size (before) etching wouldn't wreck the photoresistant layer.
Thanks.

[Gurner]

I've not had any issue - but a nice, swift, clean cut is essential ..... if using FR4 stuff, I use the office guillotine to cut (but don't tell the secretary), if using paper based economy boards (which I heartily recommend), I use a hobby table saw (the paper based stuff guillotines badly which flies in the face of logic!)

[R.G.]

Just be sure that your cuts leave enough un-squeezed stuff in the middle to test that hasn't been squashed.

[R.G.]

Sorry, hit send too soon.

Or you can do the photographer's old trick of putting down an opaque mask and sliding it sideways every so often. This leaves a photo with a range of exposure times across it in bands. And you only have to develop one sheet to tell the right exposure very closely if you are careful about how far you pull the mask back each time.

[Gurner]

Sorry, hit send too soon.

Or you can do the photographer's old trick of putting down an opaque mask and sliding it sideways every so often. This leaves a photo with a range of exposure times across it in bands. And you only have to develop one sheet to tell the right exposure very closely if you are careful about how far you pull the mask back each time.

And  if going that way, don't do as I did.....I wanted to test from 3m thru 8 minutes  with 1 minute periods (moving back a bit more of a 'masking' board each time)....remember - in my example, the 3m exposure comes at then end!

eg .  expose 1m, move cardboard, expose 1m move cardboard----->and so on, final exposiure is for 3 minutes!   (I started with the 3 minute exposure - doh!)

Also, when i spoke of the cheap paper based board ...*only* for hand soldering - just tried my first DIY reflow in the past hour with the economy paper based copper board tonight - the board had a mild explosion in or around the reflow temperature (220C) .....hmm, I had wondered why all the sites selling said "not recommended for professional use"  .....I though they meant it was simply a bit wimpier, not prone to explode! (oh how they laughed in the burns unit)

[davent]

Hello,

No problem cutting off, before etching, whatever size of PCB you need (as long as it has an opaque material protecting the sensitized side of the board if not you'd have to cut in the dark or use a safe lamp for lighting to see what you're doing.) Most boards i've purchased have an opaque material stuck to the sensitized side but i've got a double sided board that just has a couple loose pieces of cardboard to protect them once they are removed from the black opaque bag, not such a great setup.

dave