I got back the results of the free check of the design rules from FreeDFM.com that I mentioned in my earlier post, and there are a lot of problems.
First, the sfe-gerb274x.cam script from SparkFun included the Dimension layer in the top copper, but this generates traces that are far too thin (0.1 mil) to be made. The outline of the board does not belong on this layer.
Second, the Adafruit component for the Arduino, that labels the Arduino pins used 3 mil strokes, but the minimum stroke width for 4pcb.com’s silk screens is 5 mils, so there were 4103 violations.
I fixed the script that generated the top copper file so that it didn’t include the Dimension layer, and went through some of the libraries fixing the fonts so that the 0.04″ high letters has a stroke/height ratio of 13% and the 0.05″ high letters had a stroke/height ratio 10%, meeting the minimum silkscreen requirements. I resubmitted the design to FreeDFM and got
No DFM problems were found on your board!
| Show Stoppers
| We Found None!
| Problems Automatically Fixed by FreeDFM
|We Found None!|
They also provide some nice pictures of the layers as pdf files, so maybe I don’t need a Gerber file viewer after all (though the separate PDF files don’t give me any clues about possible misalignment).
I’ve not decided for certain whether I’ll go with 4pcb.com for my fabrication, but the fact that I was able pass their design rule checks (and the positive recommendation for them that I got from someone who supervises a lot of student PC board designs) is encouraging. The minimum order of $132 (which would give me 5 copies of the board) is a little daunting for a first attempt, as I’m sure I messed up something.
Yep, I sure did. In a comment on my earlier post, Mylène gave me a pointer to a trace width calculator, which I used to figure out whether I had made my ground line fat enough. The answer is “No!” If I use the cheapest fab lines, I get 1oz/ft2 of copper, which the calculator estimates would heat up 40ºC in the most constricted spot on my board. So I guess I have to push things around until there is enough room for another ¼” of wire there. Good to catch that now, rather than after fab!
Advanced Circuits does have a cheaper “bare bones” option, but it does not include a solder mask. I don’t think I want to try soldering even 0.1″ spaced pads without a solder mask, as I’m clumsy enough to have trouble with solder bridges even when there is a mask.
I also looked at Olimex, which claims very low prices (30€ a board for 1–4 boards), but I was turned off somewhat by the low-quality of their web site and the big announcement:
Note: we are in summer vacation 1-31 of August.
ALL PCB files sent after July 26th will be proceed in September.
I didn’t do it justice here: the announcement fills the screen on their site. Since I want to work on this primarily in August, I’m not willing to take a chance on their being shut down for the month when I need the boards.
Olimex does take Eagle board files directly, doing their own conversion to Gerber and drill files. This could be a nice advantage for someone who doesn’t want to bother with the Gerber files. Now that I have a script that does the right thing, though, it should not take me much effort to do the conversions myself, so this advantage is small.
Perhaps more important is that they release their design rules as Eagle dru files, so you can do your checking as you do your layout. I downloaded both their rule sets (the 8-mil and the 10-mil) and found that my design fails both. Again, the problem is with silkscreen stuff, but not the line thickness—the silkscreen outlines of some of the parts I use comes too close to the solder masks for them. I had a few problems with that even using the default design rules, but I fixed those by editing the package outlines. The Olimex rules require an even larger clearance, and there are too many different drawings involved, so I’m not willing to take the time to tweak everything to fit Olimex’s fussy rules, despite the low price.
Custom PCB offers low prices and takes Eagle files (or Gerber files, of course). I think I could get 4 boards for $90 from them, including shipping from Malaysia, but I’m still waiting for the official quote. I think I may fail their design-rule check, though, as they specify a minimum of 6mils for silkscreen lines on their design-rule page. I’d have to redo a lot of lines to meet that spec! And I’d have to write (or find somewhere) a set of Eagle design rules that match their requirements, since they have slow turnaround on checking for manufacturability (a day). They sent e-mail saying
“We have reviewed your design and it looks good for production. Total cost for 4pcs with Soldermaks & Silkscreen is USD 72.00 + USD 15.50 shipping to USA.”
If they are willing to accept 5 mil silkscreen instead of 6mil, this may be the way to go! I’ve sent them an e-mail query about their design review—whether they neglected to check the silkscreen or if their minimum acceptable line width has changed.
PCBExpress has a minimum price of $390 (for 2 boards this size).
PCB unlimited has a minimum of $230 (which would get 2 boards) for the “quickturn” pricing and $260–280 for their overseas fab (which would get 1–10 boards).
PCB Universe has $127 (including shipping) for a 4-board lot up to $229 for 10 boards (beyond that number, their standard pricing is supposedly cheaper). They have 5mil minimum space and lines, which my design easily meets. Their pricing is similar to 4pcb.com, but without the service of the free design-rule check.
Prototype PCB quoted me $229 for 3 boards.
Bottomline: If CustomPCB can handle the 5mil lines on the silkscreen, then I think I’ll give them a try. Otherwise I’ll probably go with 4pcb.com