Back when I fabricated my PCBs, I thought the next step was to buy the electronics. What could go wrong? Most components such as resistors and capacitors are ubiquitous and nearly fungible. You can swap out manufacturers and minor specs as long as the main desired value (resistance, capacitance, etc) is fulfilled-- and as long as the part is the same form factor. The latter means "it needs to fit onto your PCB in the holes provided."
My $264 order of satellite from DigiKey was short one part, intentionally. The dreaded MAX9929 Current Sense Amp. I needed 8 of these puppies for the Power supply part of the satellite. Since I'm building a flight spare, too, I needed 18. Toss in 2 more as spares and it's an even 20. Digikey had, in stock: 0. Expected arrival date was January.
Fortunately, another site had them in stock, so I ordered them. Then, later, I got an email from them cancelling the order, because they lied lied lied about having them in stock (not that I'm bitter...) Okay, not a problem. The engineer who designed the board, Gerard, suggested I try Farnell (his vendor).
Farnell doesn't have a US shop but does run an 'export' shop-- which was entirely out of the part. Wouldn't have them for 90 days. Hmm. So I went direct to the manufacturer. They're out of stock-- 12 week backorder. Worrisome.
Long story short, after trying a dozen shops going all the way to Taiwan, I could not find them. I asked Gerard if there was an easy substitute, but he noted that, with my PCBs already fabricated, a similar amp might not fit (or have different pin-outs, which is worse).
Where, oh where, could I find a supply of MAX9929 "Maxim integrated products MAX9929FAUA+ current sense amp, 0.1~28V, 8UMAX, current input bias 1.6uA, input offset voltage 6000uV, current supply 20uA, bandwidth 150kHz, voltage supply 2.5-5.5V"'s?
Back comes Gerard to the rescue! The French outlet of Farnell has them, he'll order for me, then ship. All I have to do is pay for parts, and currency difference (minimal via PayPal, fortunately), and international shipping.
Farnell France had only 82 in stock. And Gerard noted that sometimes their on-hand is lower than they list. Eek!
By my reckoning, I was buying one quarter of all the Max9929 available to potential satellite builders.
I should have bought them all. Then I'd own the TubeSat Power Management Board electronics market until February 2011, mwah ha ha!
The lesson from this is, once you commit to a given PCB layout, buy all of your more unique parts, especially ICs (the chips), before you place the fabrication order. That way, if you hit a supply problem, you can consider a board redesign before committing. Otherwise, you'll be forced to find a back alley black market satellite parts dealer, and face it, there aren't many of us in the book.
Alex
Launching Project Calliope, sponsored by Science 2.0, in 2011
News every Tuesday at The Satellite Diaries, every Friday at the Daytime Astronomer
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