Seating Crystals/Oscillators Firmly - How? - Page 1
Forum section: electronics / general

author: T4P
author_rank: Super Contributor
timestamp: August 30, 2012, 04:28:36 pm
content: 3 ways i can come up with1: Hot glue2: A+B 5min/30min Epoxy3: Silicone Waterproof SealantAny other ways?

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 30, 2012, 05:19:15 pm
content: I've seen lots of crystals (HC49U) soldered flat to the PCB, sometimes with a wire from the top, sometimes with a wire across, sometimes just soldered.

author: SeanB
author_rank: Super Contributor
timestamp: August 30, 2012, 06:29:20 pm
content: Why do you want to attach it firmly. A wire soldered to the crystal can normally works well up to a level, and generally if it will be exposed to extreme shock you will want to first seal the board in a slightly flexible encapsulant then pot the whole unit, or use a acetoxy free silicone to pot the whole board. High fill superglue works well, at the expense of some bloom on the board, to mount the heavier components before doing potting.

author: T4P
author_rank: Super Contributor
timestamp: August 30, 2012, 06:43:12 pm
content: Shock is not an issue on the entire board but chassis vibration is making my tuning fork crystal to go haywire

author: SeanB
author_rank: Super Contributor
timestamp: August 30, 2012, 07:11:56 pm
content: So what you want to do is isolate the entire oscillator from vibration. Use an acetoxy free silicone to blob it to the board on long leads with a space below it, but preferably you want to have a daughterboard which is mounted with a flexible cable and a flexible silicone block to absorb the vibration. Then you superglue the crystal case to the small board and rely on the flexible support to absorb and damp.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 31, 2012, 01:34:00 am
content: if you want to fix an ocsillator firmly to a vibrating board, it will vibrate with the board because a firm board fixed to a vibrating chassis will also vibrate. if you want to isolate the vibration, use an air pocket aka floating on its lead? the longer the lead the better? no? or just press the oscilator hard to the board and solder the lead? are you making high end equipment? rubber "damper" on the chassis fixing the board cant do?

author: T4P
author_rank: Super Contributor
timestamp: August 31, 2012, 04:18:57 am
content: Quote from: Mechatrommer on August 31, 2012, 01:34:00 amWell yes i forgot about damping - thanks there mechaQuote from: SeanB on August 30, 2012, 07:11:56 pmI can use silicone and dampingHigh precision portable stuff here that's why. No possibility of a OCXO because well power hungry and pretty huge

author: ColinB
author_rank: Contributor
timestamp: August 31, 2012, 07:54:04 am
content: Check out the glue (silicone or hot melt) on the crystal in Leo Bodnar'sFormula 1 steering wheel teardownrecently posted on the forum.

author: Andrei
author_rank: Contributor
timestamp: August 31, 2012, 06:09:45 pm
content: Keep in mind that if you try to dampen the entire board and have accelerometers on it. The high frequency vibration will turn into lower frequency vibration, and just about destroy your accelerometer data. This happened to me while working on personal project. The best solution I came up with was to leave the board mount as rigid as I could such that the high frequency vibration would be out of the measurement range for the accelerometer. Dampening just the crystal is of course fine.

author: T4P
author_rank: Super Contributor
timestamp: August 31, 2012, 06:37:41 pm
content: Quote from: Andrei on August 31, 2012, 06:09:45 pmYeah i'm aware of that, i call dampening for accelerometers "Mechanical Frequency Filters"That's what my friend taught me