Discussion
andrew@lab:~$
kentrf: Interesting writeup!Today I learned about TCXO.If anyone else are curious, that component cost about $2 per piece.
myself248: I've always been cautioned against ultrasonic cleaning of boards that have crystal oscillators, and indeed it's in most XO datasheets.I've also heard that one shouldn't trim the leads of a through-hole XO before soldering it into the board, since the mechanical shock of the lead breaking can ring the whole package and similarly shake it apart. I'm curious if anyone here has seen that in practice!
jacquesm: That's a very cute domain name. Thank you whoever wrote this up and posted it, I'm in the process of building something that has a crystal on it and I did not realize this was a risk.
the__alchemist: Yea! Useful if you need precise timing under temp swings. I use them for UAS LoRa radios. Def more expensive than a normal XO!
jacquesm: But cheaper than OCXO and far less power consumption too. Also (much) less stable.
jacquesm: Oh, that's a good one, I can see how that would put a lot of g's on the package. I think this will be a factor depending on the weight of the total assembly. If that weight is significant it will dampen the shockwave.
the__alchemist: I went down this rabbit hole a few years ago, and couldn't find an actionable answer on if this is OK or not. Sounded like "No, you shouldn't", but almost every PCB I've designed (or used?) has at least one, and I know ultrasonic cleaning is a thing, so I'm not sure how to reconcile these.
galangalalgol: Compensating for the temperature will never be as accurate as actually controlling it (O is for ovenized). I keep reading about chip scale atomic clocks coming down in price but I've yet to see them as the oscillator in anything mass produced.
namibj: The divide by two is to get the quartz small enough to fit that package.
ACCount37: There is no single answer. It depends on the exact components, their sensitivities, frequencies and energies used, and how much failure risk are you willing to take.Rule of thumb: one simple xtal per board in small manufacturing runs (4 digits or less) means you're fine.The larger your manufacturing runs are, and the more sensitive components you have on your boards, the more careful you want to be. Components can easily make the difference between 0.2% failure rate and 2% failure rate, and that 2% failure rate bites when you push units by hundreds of thousands.Of course, there's always a chance of you getting a perfect match of the exact intensity and frequency used on a given manufacturing line, which you didn't know, with what happens to kill your specific components at a disproportionate rate, which you also didn't know. But it's a pretty low chance. Feeling lucky?Because yes, it's not actually worth the engineering/support effort for you, your manufacturer and your part vendor to actually put the thinking cap on and characterize all of that shit for a typical low volume run. So luck it is.
