No room for an accelerometer on your PCBA?

Friday, June 22 2018

Finding a place for your accelerometer in your PCBA during HALT can get difficult.

A miniature accelerometer on a densely populated PCBA

As PCBA’s get more densely packed, finding a place to put an accelerometer during HALT can get difficult. And, as we all know, monitoring the acceleration at the board level is very important in HALT - it’s the only way to clearly understand the stresses delivered to a PCBA when using Repetitive Shock vibration. I often find that there simply isn’t a place to put an accelerometer without putting it on top of feed-throughs, and after I’ve used an accelerometer a few times, the anodization on the base gets scratched enough (from removal of the adhesive after a test) that I can’t trust its electrical isolation. I’ve tried putting a piece of Kapton tape on the board and gluing the accelerometer to that, but at higher g’s the tape under the accelerometer can pull up, affecting the readings. I recently found a solution to this problem that I thought I’d share.

Just put a thin layer of Loctite 444 where you want to put the accelerometer. Warm it up a little with a hot air gun to make it less viscous and tap the PCBA gently, so it flows to a nice flat surface. Then drip a little accelerator on it to make it set up, and clean it up with some alcohol. Now, you’ve got a flat, electrically isolated surface for your accelerometer, and there’s no risk that your change will affect vibration transfer.

If you try this, let me know how it works for you.

And remember - If it’s not broken, you’re not done yet!