SOFTWARE SUNDAY – Gerber Viewers. Nothing makes an engineer more nervous than a “tape-out” – that moment you send files off to a manufacturing house for PCBs (or chips). Will the returned product be correct, letting you continue onto manufacture? Or will there be a (dumb) mistake, setting you back 3 weeks and hundreds to thousands of dollars? Even the best engineers I know still get antsy and nervous in the lead up to a release!
That’s why its so important to do everything you can to avoid problems. Now, there’s not one engineer out there who has done nothing but fab perfect designs each time. Heck, even Microsoft had XBox manufacturing problems, they happen! But every step you take to avoid an easily-fixable problem is worth your attention.
Before we send of PCBs, of course we do a ERC/DFM check inside the software but even then, we always take a look at the final GERBER files before they are zipped up and sent off to the fab house.
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I did a couple of boards a while back… 2 gerber viewers, and a hand (er, eye?) inspection of the files… they still came back wrong. I’m not sure how but the board house’s proprietary gerber handling system managed to drop flashes in a few random spots on one of the boards, and used the wrong aperture for a few pads on the other one.
Although the boards were salvageable with an x-acto knife under the microscope; I no longer use that board house, due to the lack of good communication after I reported the problem (it wasn’t a confidence-inspiring experience).
Oh, and if you are on a Mac, I’ve had good luck with using Pentalogix’ free version of ViewMate ( http://www.Pentalogix.com ) under Wineskin ( http://wineskin.doh123.com ). I’m updating it now to the latest version to try under Lion – we’ll see how that goes. 🙂
Oh, and by “hand inspection” I mean in a text editor (TextWrangler, in specific), line by line (yes, I can read a gerber file – admittedly not the most pleasant task in the world, but when it needs to be done, it needs to be done).
Since I do most of my work in KiCad, I’ve just been using the integrated gerber viewer, Gerbview, for most projects, and it’s worked out pretty well. I’ve compared it to a couple other viewers, but was happy with sticking with free opensource Gerbview.
Any hints on what a gerber viewer might show that doesn’t appear in erc/drc/viewable/printable views of the same board? Sure, you can detect “mirrored” layers (that may or may not be what was required in the first place), but I’ve found that to some extent a gerber viewer is another piece of SW whose configuration might be wrong. Or forced “correct” in ways that don’t duplicate what a board house will do.
I use gerbv on a Mac (which was quite a pain to get compiled!) One thing that comes in handy is that you can set color mixing to “xor”, which can highlight differences or similarities if you carefully pick your layer colors. I’ve been working on a tool that processes EAGLES backup .b#n board files and uses gerbv to highlight the changes (almost usable!)