Achieving a smaller trace width in Eagle

[evandude]

So, this has been bugging me for a long time now (ever since I got familiar with Eagle, and got my toner transfer PCB methods down well enough to make decent boards): the narrowest trace width you can select in eagle is 10 mils.

Maybe I've just missed something that everyone else has known about for years, but I had never been able to find any way to get a narrower trace width (or, for that matter, any DIFFERENT trace widths than those that were on the drop-down list) - not in the options menus, not in the help file, and not in a series of google searches for info. It seemed either nobody knew, nobody cared, or everyone thought it was so easy to do that it wasn't worth mentioning.

Anyway, I finally stumbled upon the answer today in one of my "there has just GOT to be some way to do this" sessions, sitting down and poring over every possible option... Not only that, but I stumbled upon two different ways of doing it. So, just in case anyone else was wondering:

If you select the CHANGE tool (wrench icon), go to "width", and go all the way down to the bottom of the list you'll see "..." which pops up a box and lets you type in whatever trace width you want, in inches in my case (so for 5 mils, enter 0.005) This not only allows you to change any existing traces to this width, but it also adds this new width to the drop-down box so you can select it for new traces. This wasn't that intuitive so I'm not surprised it took me a while to find.

Alternatively, (and of course I figured this one out only after stumbling onto the other method), you can just select the text in the drop-down width box and just type in your desired width there. It seems to like to replace whatever width you had selected before, so it's probably a good idea to select the first option (zero width) before typing in your new one.
This method seems like it should have been somewhat more obvious, or at least makes more sense in retrospect, but then again typing a custom value into a drop-down box is not exactly a "normal" input method in my opinion.

Either way, it doesn't appear that any custom values you add to that list will stay there when you change to a different board - if anyone has any info on how it might be possible to "globally" add this custom width as a value that is always selectable by default, I'm all ears. But, since all you have to do is type it in once and it's on the list for a particular board, it's not a big hassle even this way.

Now, feel free to tell me I'm a fool and that you've all known about this for years

 

[Sceadwian]

You're not a fool, but I have known about that for years. Really depends on who programmed the application and what they used for it, but older style windows programs use that kind of interface readily.

 

[justDIY]

what happens if you define custom sizes in the net classes setup ... will they show up in the drop down list?

I guess that isn't global to all projects, but at least maybe they'll be there every time you load up that project?

 

[justDIY]

i should add that I don't use the mouse for most of the menus now - I've discovered eagle understands abbreviations

for example instead of clicking change, width, 0.056 ... I just type:
chan wid 0.056

oh and a big time saver for arranging parts ... you know how it likes to add them all in a big mess outside the usable "free" area? well, using abbreviations it becomes real easy to arrange parts, especially tedious ones like LEDs and resistors. put the mouse where you want the part and type mov led1 then click - part placed! now press UP ARROW, backspace, 2 (text box shows mov led2), enter, click - second led placed. on paper it reads like a lot of steps, but its a LOT easier than moving back and forth with the mouse - especially if you're zoomed in placing small parts.

 

[cadstarsucks]

So, this has been bugging me for a long time now (ever since I got familiar with Eagle, and got my toner transfer PCB methods down well enough to make decent boards): the narrowest trace width you can select in eagle is 10 mils.

Ummm... there is some logic to the min trace width... High tech PCB houses only go down to 8/8 spacing before they start charging a premium.

D.

 

[evandude]

Ummm... there is some logic to the min trace width... High tech PCB houses only go down to 8/8 spacing before they start charging a premium.

Fair enough, but there's still a difference between 10mil and 8mil. That, and I make my own boards, rather than getting them made professionally, so "what I can fab" is more important than the limitations of a commercial manufacturer.
I don't exactly plan to use <10 mil traces on a very regular basis, but it's certainly nice to have the option when needed...

 

[cadstarsucks]

Fair enough, but there's still a difference between 10mil and 8mil. That, and I make my own boards, rather than getting them made professionally, so "what I can fab" is more important than the limitations of a commercial manufacturer.
I don't exactly plan to use <10 mil traces on a very regular basis, but it's certainly nice to have the option when needed...

True... I do on a regular basis, but then I am working with parts whose pin spacing is 15-20 mil and 100 or more pins on a regular basis.

I would be interested in knowing what you are able to get reliably and what techniques you are using if you get that kind of spacing at home. The thing is I have trouble believing you can get better than they do regularly. On the other hand, I can believe that one could do well enough to make a PCB that one could patch together gaps and cut bridges to make work, but it becomes very tedious.

D.

 

[evandude]

I use toner transfer with press-n-peel blue transfer sheets. The edges of the pattern aren't perfectly crisp like you get with the photoresist method, but they're more than good enough to do 10 mils, and as I said I'm confident I could go at least a bit lower before I start having real troubles. I expect the etching process to become more of a problem at some point - under-etching (under the sides of the resist pattern) becomes much more of an issue with extremely narrow traces, so I'd have to start more carefully controlling my etching process.

Again, I don't expect to NEED <10 mil traces very often, because if a board needs very much fine-pitch work it probably also needs to be double-sided, which is a lot more annoying with DIY boards - no plated-thru holes, and lining up both sides takes a lot of time. But, for squeezing a trace or two through some narrow areas, or doing a simple breakout board for a very fine-pitch device, it could be useful to drop below 10 mils.

Some pictures of mine (10 mil traces all around):
https://eegeek.net/electronics/pnpb_transferred.jpg
**broken link removed**
https://eegeek.net/electronics/pnpb_etched.jpg

 

[cadstarsucks]

I use toner transfer with press-n-peel blue transfer sheets. The edges of the pattern aren't perfectly crisp like you get with the photoresist method, but they're more than good enough to do 10 mils, and as I said I'm confident I could go at least a bit lower before I start having real troubles. I expect the etching process to become more of a problem at some point - under-etching (under the sides of the resist pattern) becomes much more of an issue with extremely narrow traces, so I'd have to start more carefully controlling my etching process.

True... it is the under-etching is the problem... I have never used the press-n-peel stuff, but I have used toner transfer for a couple little things for myself. I keep thinking I have to convince my boss to get an LPKF system. They will do the fine pitch double sided pseudo plate thru boards for about $8K.

I realize that is useless information for hobbyists but it is interesting. It puts copper clad through a milling process on both sides, drills the holes, the uses the vacuum hold down to draw a conductive polymer through the holes.

D.