Fine Traces And Undercutting

[Village Idiot]

I'm making a PCB for some surface mount devices, and in order to fit the devices, some of the traces will have to be 0.25 mm wide. I'm using toner transfer to do this and was wondering if anyone has done traces this thin with toner transfer, and whether there have been any problems with undercutting.

[Sch3mat1c]

That should be okay. I normally kept my traces around 15 or 20 mils (0.37-0.5 mm), but I always had spotty results. Others have achieved much finer detail reliably; if you're one of them, don't worry about it. Most manufacturers go down to 5 to 7 mils (~0.15mm), 10 should be achievable.

As for undercutting, well just don't undercut it then! Lots of circulation ensures even etching. That's something I never got much of, either; large areas always etch faster on the sides, at least with poor flow. It also helps to cover large open areas with copper pours, reducing the burden on the etchant -- which is good practice, electrically, anyway. If you aren't using the area for signals, ground it, you can only make your circuit better!

Tim

[Village Idiot]

Yes, I generally try to keep as much copper on the board as possible. Also, I'm using boards with only 1 oz. copper, so they should etch fast and minimize undercutting.

Looking at it again, I was also able to increase the trace width to 0.35 mm. We'll see what happens.

[Village Idiot]

It turned out just fine. Probably didn't hurt that I recently put in a new toner cartridge.