minimum track width for 70um boards

[Simon]

I'm thinking of making something with 70 um copper (2oz/sqft), will I be ok using 0.64mm traces ?

[DJPhil]

I had to do the math on that one. I believe 25mil (0.64mm) should be fine, but it really depends on your etching process. Many board houses will go down to half that, but they've got the good equipment to guarantee it works.

I just did a 1oz board with a 15mil (0.381mm) border and it came out ok even with my crappy etching skills. I had a bit of undercut in spots, mainly because I'm really sloppy with the FeCl + sponge method. I haven't finished it up yet but it looks like it'll hold up fine, and I can always coat it if I get worried.

Hope that helps.

[Simon]

well if I ever made it in number I would probably use a board maker and might get away with 35 um copper on prototypes although I could give 70 um a go

[djsb]

Are you using the thinner copper because it's cheaper or for some other reason?

David.

P.S DOH! Should've asked what the standard weight was before asking and read the OP message properly. Thats what you get when posting when youre tired.

[RayJones]

isn't 2oz thicker than the usual 1oz?

Going by recent discussions with Simon, I'd say he's planning on monitoring significant currents, hence the thicker copper, hence more concern about undercutting.

[EEVblog]

25 thou is massive, no problems at all.

Dave.

[Simon]

isn't 2oz thicker than the usual 1oz?

Going by recent discussions with Simon, I'd say he's planning on monitoring significant currents, hence the thicker copper, hence more concern about undercutting.

correct, standard boards are 35 um (1 oz) as I'm passing 20+amps I thought 70 um would be advisable but do have SOIC/SMD parts with 0.64mm tracks, also going into a car environment I think toughest is best.

Yes I've heard undercutting is an issue with thick copper but did not know at what widths it becomes critical