>
> Would this affect etch-under at all? My latest board had trace
> thinning to the point where many were missing completely, I've been
> "bloating" my films to compensate but a better process would be a
> better solution.
>
What are you using to hold your film to the blank PCB? You have to make sure the printed side is against the board, and it has to be absolutely flat. Use a piece of relatively thick glass, 3/16" or so that won't flex, and hold it against the board with a decent amount of pressure. If you're using a light box, it works well to set a brick on top of the board to hold it down flat on the film. Many printers have trouble getting a nice solid black on transparency film too, vellum paper tends to work better, it's transparent enough to UV, and a laser printer will lay down a nice dark print on it without any warp or ripple.
I've only made a handful of photo etch boards myself, but I've never had any thinning at all. I've always used a 15W bug zapper tube and exposed for 4-5 minutes.