Vibration testing is the shaking of an assembly (or, sometimes, a component) to see how it responds to a vibration specification that is chosen to replicate an acceleration of a real life environment.
Increasingly, random vibration testing is chosen rather than swept sine as this has been determined to most closely reflect real life movement. Random vibration can be difficult to visualise, but all frequencies are simultaneously present, with their levels varying to bring about an overall power level. Damage is most likely to occur when the device is vibrated at its resonant frequency, and considering that many applications are subject to frequencies up to 2000Hz, resonances are impossible to avoid.
The vibration specification that a power supply is required to meet (like MIL STD 810) must be considered throughout the design phase as vibration issues can be very difficult to deal with later. If you have a good CAD package (like Solidworks) then some basic modelling of chassis and PCBs can be analysed to good effect early in the design. Otherwise, good visualisation is required – mountings at max 50mm centres, little overhang of boards and common board supports close to interconnects.
Heavier components, like magnetics, that are >5g need bonding down or be mounted on the chassis. The epoxy resin glues of choice are Emerson & Cuming type 45, now known as Henkel Loctite Ablestik 45 (a flexibilised epoxy) or Araldite 2014 (a rigid heat resistant epoxy).
So, how to choose? For most applications the type 45 is good, especially where a little bit of ‘give’ can be tolerated. 2014 is for the more problematic situations where a really firm bond is required. Of course, you could opt just to use 2014 but rework can be quite challenging, much more so than type 45. Either way, make sure that the surfaces to be glued are really clean with IPA or similar.
Remember it’s not so much the vibration that causes the problems but the relative motion between parts, all excited at a different frequency. This is particularly true for board interconnects which can suffer contact fretting. Interconnects take many forms, from the sophisticated ‘hyperboloid’ to simple ‘leaf’ springs. Avoid any that have only one point of contact.
Capacitors pose some specific problems, and it’s vital to understand the type of capacitor involved. Aluminium electrolytics must in themselves be able to stand the vibration levels. The type that is best have a case that ‘pinches in’ to the windings inside. These also are better thermally.
High value multi-layer ceramics tend to be quite tall relative to their base footprintand and need handling very carefully. Bonding with either of the epoxies listed earlier will likely cause too much strain over the temperature range. The glue used here has to have slight flexibility that remains fairly consistent over the temperature range – and it’s usually best to lay such parts down if you can.
Our team of talented power designers ensure all our products are created and assembled to ensure maximum efficiency when under vibration/movement pressures. We have state of the art machinery which allows us to fully test our products, ensuring they are exactly to your specification.
Talk to a member of our team today to discuss your vibration proofing and custom power supply requirements. You can also view our military products or read more insights from the team in articles below.