>>> ... MEMES devices are usually destroyed by ultrasonic cleaning > > Does the same apply to assemblies ultrasonically welded into a box I > > wonder? If so, this post could have saved us a bit of future strife - > .... if open ultrasonic cleaning essentially always destroyed a given MEM= S > device it would almost certainly be possible to produce a housing such > that, by design, ultrasonic sealing of the housing almost always destroye= d > the MEMs device. If you can do it by design then Murphy can too. Equally, > it would be possible to produce a housing by design where destruction > almost never occurred. Murphy will work on "optimising" almost-never. On 18 December 2014 at 22:58, Richard Prosser wrote: > Yes, I was thinking it is a consideration, and worth checking up on. I'm > not even 100% sure the product is going to have MEMs in it, but it's quit= e > likely and I know ultrasonic welding is being considered. It might be as > simple as providing some damping to the pcb. We do carry out significant > vibration & drop testing, but this is a bit different. > Obv > io > usly, ultrasonic cleaning will apply vibration pretty well directly to > the components, but welding could excite resonances not otherwise exposed= .. > Here is some confirmation that it MIGHT be an issue. This is from a technically very experienced friend who I copied my prior comment to offlist. A crystal and a MEMS device are obviously different but also have some similarities. It sounds like doing some tests on a sample board with a suitable sensor during welding may be a very worthwhile thing to do. Ken said: One of our customers has been using ultrasonic welding for many years to seal a PCB assembly in a plastic housing. The PCB has among other things on it a 32.768kHz crystal. Such crystals from many manufacturers do not like this treatment and many die during welding leaving some that are walking wounded. Some products from some manufacturers seem to survive much better than others. Moving the crystal on the PCB suggests that the problem is worse in some positions compared with others - though how you would determine a "good" position other than by trial and error I don't know. Life is so rich and full :-) Yet another can of (vibrating) worms. Russell > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .