karplus4arduino

2011 July 19

More on PC boards

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

Congratulations!
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

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6 Comments »

  1. Have you considered Batch PCB? I haven’t used them myself but read positive reviews in Make magazine as well as in an IEEE Spectrum article on hobby projects (sorry — can’t find either reference at the moment). This caught my eye: “With BatchPCB you can submit any design at any time and see if you will be able to use our service. Our DRC bot will happily scan your design and send you an email within 10 minutes letting you know the status.” They spec 8mil traces and 8mil clearances — I’m assuming that that refers to copper layers, not silkscreen. (My experience is, as Custom PCB wrote to you, that the manufacturer simply uses their min. silk screen stroke width, regardless of what’s in your design. An extra mil is unlikely to make it illegible.)

    BatchPCB collects submitted designs, panelizes them, and send them for manufacturing together. As a result, you pay $2.50/ sq. inch (rather than by the panel), and can order a single board if you like. It looks like about a 3-week turnaround, though — maybe too long.

    Comment by Mylène — 2011 July 20 @ 09:28 | Reply

    • Actually Kevin, if you look at 4PCB.com, under the specials they have a “Student Discount” that works for any .edu address, which allows you to buy one of their $33 specials (2-layer, silk screen and solder mask), with and you only need to order one board, so the shipped price is <$50, for excellent quality.

      Also, the size they allow is significantly larger than eagle allows, so you can tile a number of your various attempts and cut them apart with a shear (identical tiles will cost you an extra $50).

      See this page: http://www.4pcb.com/index.php?load=content&page_id=134

      Comment by elkaim — 2011 July 20 @ 10:31 | Reply

      • I had seen the student pricing at 4pcb.com, but I’ve always been a little troubled by the idea of claiming a student discount. I prefer systems like Apple’s where the discount is an “educational” discount and refers explicitly to both teachers and students.

        The idea of getting multiple boards for $33 is attractive though, and 4pcb does seem to have specs for high-quality (5 mil lines).

        Comment by karplus — 2011 July 20 @ 11:17

      • I’ve consulted with a couple of “ethics advisers” (my wife and Gabriel) and everyone is telling me that because this board is destined for the Santa Cruz High School Robotics Club, it easily falls under the “student project” guidelines, though they’ll just be soldering the board, not designing it.

        Gabriel also told me where I can get free access to a board shear, so the only problem now is figuring out how to submit a multi-panel design, since I’ve already hit the maximum size limit for the free version of Eagle.

        Comment by karplus — 2011 July 20 @ 13:00

    • The Batch PCB site looks good: a quick upload and fast feedback on the pictures worked fine. The price is good also: $31 a board with no minimum order (and I don’t have to lie and say I’m a student). They also offer a service like many of the on-line T-shirt printing companies: you can sell your boards to others (though the pricing will probably be much higher than with a regular production run).

      The 8mil minimum for traces and clearances is rather high though—other cheap places are using 5mil or 6mil. That implies to me that they have a really cut-rate manufacturer using old processes.

      Comment by karplus — 2011 July 20 @ 11:13 | Reply

  2. On https://karplus4arduino.wordpress.com/2011/09/27/4pcb-com-sticklers-for-the-50-multiple-image-surcharge/ I report that 4pcb.com is no longer allowing tiling (not even of different projects) for the $33 board, so for tiny boards BatchPCB.com is cheaper. For the hexmotor board, it is about the same price from BatchPCB or 4pcb.

    Comment by karplus — 2011 September 27 @ 17:17 | Reply


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