Nordic Coaster


Oh PCB layout. How you spite thee.
What's a 'coaster' you ask? A coaster is something that sits under a coffee mug (or beer glass) and prevents the vessel on the coaster from leaving a visible ring on a table. It's also a name for a completely screwed up PCB.
http://www.sparkfun.com/tutorial/news/Nordic-Coaster-1.jpg
This is a panelized PCB design. 'Nordic-FOB' is a design that I've been working on and is ready for production. The board has an ATtiny combined with a Nordic nRF24L01 radio, all housed inside a Polycase keyfob enclosure. The 20mm coin cell battery runs the system for a couple years. You hit a button and the Nordic radio chirps the wireless information over 2.4GHz - kind of like the keyfob for remote entry of cars. Sounds cool, if it worked. What's wrong you ask?
http://www.sparkfun.com/tutorial/news/Nordic-Coaster-2.jpg
That is wrong. What's that?
http://www.sparkfun.com/tutorial/news/Nordic-Coaster-3.jpg
That is a tiny, tiny disconnect from one of the pins on the nRF24L01 to ground. See that little line? That's an airwire indicating there is not yet a connection. There should have been, because the ground pour should have poured onto that pad. But Eagle failed me. I failed myself. Because of this tiny (and I mean 0.005" tiny) disconnect, the board is completely worthless. I've been laying out PCBs for years, and I still produce coasters.
http://www.sparkfun.com/tutorial/news/Nordic-Coaster-4.jpg
Life after airwires.

Comments 2 comments

  • A test to avoid this is to route the board then press the “Ratsnest” button. If it says “nothing to do” [bottom left of the display] all is routed, if not you’ll get a count of airwires which are unrouted signals. Sometimes it is very hard to then find them still, but at least you know.

  • Surely a little greenwire would connect that pin? It’s useless for production, though.
    I ran into an issue when using Eagle 4.16r2 last year. My company had not yet purchased the upgrade to Eagle 5, and we were hesitant to migrate all our PCB design to the new version. I was working on a 4-layer board and had left the internal layers turned off to suppress the visual “noise” that internal layers can create. I ran my DRC checks and it found no errors, but when I got the boards back from fab, there were wires crossed on the internal layers. Eagle 5 will catch DRC errors on inactive layers, but 4.16 won’t! So I had a whole pile of coasters, too!


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