Critical Link’s System on Modules use a SO-DIMM connector, and we sometimes get asked just how well this type of connection will stand up to shock and vibration for applications that really get a workout. This is a good question, and if the answer were “it doesn’t”, customers with apps where there’s a whole lot of shakin’ going on would be looking at designing – not plugging – their communications module in. And we all know that a full custom design is more expensive than something that’s off the shelf.
So we looked for a way to make our SO-DIMM’s more rugged. And to do it cheaply.
But before revealing our secret sauce, I first want to say that SO-DIMM’s perform better than people might think. To begin with, the lever arm is not all that long, and the mass is not all that high. But what we added to make sure that the module wouldn’t shake loose was mounting holes on the back end. These are used to secure the connector in the socket, so shock and vibration aren’t a problem.
We, of course, worked with our customers to perform some shock and vibration testing to make sure that this would work in their application, checking out how the module would survive under a couple of scenarios.
In the first test, we subjected a board to random vibration of 50Hz – 5000Hz starting at 6Grms level. The vibration level was increased from 6Grms to 20Grms in 2Grms increments. The dwell time at each level was 30 minutes where the frequency was varied between 50hz to 5000hz.
For the second test, we tested for both vibration and shock. On the vibration side, we varied the vibration from 20Hz to 2000Hz for two hours in each of the three perpendicular axes at an acceleration spectral density of .04 G**2/Hz. For shock, we dropped the DUT along each of the three perpendicular axes at 20 G’s with a 1 mS duration for a total of 18 shocks.
The boards passed both tests.
And, just to put this into context, by way of comparing our tests to real life, here are the vibration levels experienced in some vibration-intensive situations:
- Turbine engine vibration = .03 G**2/Hz
- Rail cargo = .002 G**2/Hz [0 -> 350Hz]
- Jet aircraft cargo = .01 G**2/Hz [11 -> 2000Hz]
- US Highway truck = .02 G**2/Hz
So the answer about a SO-DIMM connector standing up to some pretty rugged situations, the answer is “yes, it can.” All it takes is a couple of small standoffs to hold it in place.