My plan was to cheaply acquire good quality PCB boards sufficient for 2 Tubesats-- the mission satellite and a flight spare. Many companies exist that can turn your plans into small quantities of finished PCB boards, at reasonable cost, in just a few weeks. What is 'reasonable cost'? For boards a few inches in size, as low as $25 for a single board. This is the result of my 'experiment' trying multiple PCB fabricators. Ultimately I settled on three best candidates and then checked who delivered the best final product.
For those of you too impatient to find out why and how, here's my summary. My favorite for price/performance was PCBInternational.com, whose DIY special of 100 square inches of board for $99 rocked. I would also recommend PCBNet.com if you just need 1 or 2 boards, as their intro special of $25/board is very hobbyist-friendly. And a nod to Sunstone.com for their web interface and reasonable prices; while slightly more costly than the others, they had the easiest ordering process for a novice like to me.
And now to brass tacks-- the whys and hows and who elses.
CAD? PCB? Gerber?The suggested default TubeSat configuration includes the CAD files necessary to print the Power, Antenna, Microprocessor, and Transmitter PCBs and as well as the solar cells. All you have to do is fabricate the boards. There's a standard spec called 'Gerber files' all fabricators accept.
There are 8 standard files that cover the copper, solder mask, and legend layers plus an overall outline and where you want holes drilled. Make sure you have your PCB 'Gerber' files (aka 'Gerber RS-274X files'),
created from a CAD program such as KiCAD. These will include, for a
2-layer board, up to 8 files as listed below. For a 2-layer board, you could squeek by with just 3 files-- you can skip the 'silkscreen' layers if you don't need labels, and you can get by with just one solder mask if it's a one-sided board (no solder traces on the bottom). But all the TubeSat boards are fully defined 2-layer boards, so let's move on.
A generic set of Gerber files to order PCB boards includes:
- Top (components side) layer
- Bottom (copper side) layer
- Soldermask for top (component) side
- Soldermask for bottom (copper) side
- Silkscreen labels for top (component) side
- Silkscreen labels for bottom (copper) side
- Board outline (or, default is 'rectangle that fits everything')
- Drill holes (.drl file, else no holes will be drilled)
A default single TubeSat requires 4 different octagonal boards, each about 3.5 inches by 3.5 inches in size, two-layer. It also requires 8 5x1 solar panel boards.
My Criteria for 'a good PCB vendor'My criteria was: 1) price, 2) ease of ordering/confidence with webtools, 3) did not have to use the telephone. Sorry, if I need to talk to a sales person to order a board, you're off my list. I'm a hobbyist, not a factory. If you mix my criteria #2 and #3, you'll also see 'fairness'-- I wanted a straight price known in advance. Call this 'clarity', perhaps.
I wanted at least 2 sets each of 4 boards (so I'd have a flight spare), plus 20 solar panels, so my orders ranged from 2 boards to 20, never more. Most came in at $25-50/board shipped. Really, the price breaks kick in at 10+ or 20+, but I wasn't able to get enough response from other TubeSat builders to really build a group order, so these are my 'solo' prices.
For the three, here's the prices: Sunstone, $50/board, PCBNet, $25/board, PCBInternational, 3 each of 3 designs for $184 implying $20/board. This includes shipping, on a 10+ day order (no rush). However, if PCBNet drops their special, they move to $80/per board for 2+, $44/per for 4+, and $20/per for 10+. Do the math and there's no point in ordering less than 10 from PCBNet non-special, as it's the same total cost.
Some web boards have reported erratic quality with small batch runs, so spreading your order among multiple vendors is a good way to ensure against quality control problems. Plus I like shopping.
Places I tried that failed my test (for 2 of a single board design) include:
- apcircuits.com: web quote was $72 but final price was $118 if I wanted solder&silkscreens (!?!) plus $28 shipping.
- 4pcb.com: quote $87.50 per for either up to 5 or min 5 (not sure), no tooling,
- pcbexpress.com: $121/per
- pcb-pool.com: $66/per
- pcbfabrication.com: had a $42.65 '1st time fee', $25/per plus shipping
- ultimatepcb.com: $80/per + $45 shipping
- ssl8.pair.com 'pad2pad': $121 for 2
- protoexpress.com: $83/per for 2, $43/per for 4, $11/per for 20, then requoted $3/per for 3
- sfcircuits.com: $67 per for 10+, way higher below that
- quickturnpcb.co.kr: $55 per for 4 (min) + $50 shipping
Again, I invoke 'clarity'. If I can't navigate your site, supply my Gerber files, and get the boards at the price you tout, I'm sorry, you're off the list. Extra fees, unclear specifications, or weird quantity breaks will not help you close the deal. A PCB board expert might handle that, but as a DIY-er, I want clarity.
And yes, I accept that "PCB Board is redundant", like saying an "ATM Machine".
ResultsThe boards arrived and preliminary inspection shows all boards seem viable, and the alignment seems clean-- but I haven't done complete circuit/lead testing yet. I have begun soldering pieces in, though, and am happy to report all three vendors completely failed to screw up (for the ironically impaired, that means 'they done good'). Here's my synopsis, including time from order to arrival at my house.
Sunstone.com, was $50 per board, took 16 days. (As a separate sunstone order, solar cells were $14/per for 20)
PCBnet.com, web special of $25/board, took 10 days.
PCBInternational.com, 100 sq inches of board at $185 total yielded 11 boards (3 types)! $16/board, 17 days.
Note that if you want to order 10+ of each board, you can just skip this entire column. Most PCB fabs are very cost-effective at that point. My analysis is only for people trying to minimize their costs for very small (2-3) quantities.
SuggestionsAs stated earlier, a Tubesat requires 4 'main' boards (CPU, Power, Antenna, Radio) plus the solar cells. Sunstone and PCBnet are 'per board', while PCBInt'l was in square inches but with a maximum of 3 designs per 'slab;
So, all else being equal, one path is to order two sets of 100 sq inches from PCBInt'l of:
(10 or so) Solar cells, plus two copies of 2 of the 'main' boards
(10 or so) Solar cells, plus two copies of the other 2 'main' boards
Yes, I'm being lazy and not calculating the geometry for you--- actually, I'd estimated 8 main boards on a 100"^2 slab and they gave me 11 so they do a better job fitting than I do!
That'll run you $370 including shipping (US) and give you enough parts for 2 satellites, plus likely a few extra boards left over. And for only $35/slab, you can increase it to 175 sq inches each, which nearly doubles your yield and gives you enough for 3-4 satellites. They have the best price point for this sort of 'multiple designs, small quantities' needed, their web interface was good enough, and their shipping time was on par with the others.
RisksYou want to simultaneously order spares (in case you screw up during assembly) yet not buy too much (in case you get a bad batch). Several of these prices might be intro rates or specials and may change in the future. Ultimately I can't prove these are the 'one true path' of PCB. But for small quantity 'hobby' ordering for Tubesats, I think these are viable choices.
Launching Project Calliope, sponsored by Science 2.0, in 2011
News every Tuesday at The Satellite Diaries, every Friday at the Daytime Astronomer