Many components are exposed to vibration and must be designed to survive the environment. Vibration environments can come from nearby rotating machinery, movement of the component, or even more extreme sources like rocket engines. Vibration can damage components either by exerting enough force to make the stresses exceed the yield point, or by creating fatigue that over time ultimately results in failure. In electronics these failures often exhibit themselves as broken solder joints that disconnect components from the rest of the circuitry, but failures can also manifest as broken components, PCBs, standoffs, or damage to the chassis / housing. Another effect that vibration can have is causing temporary disconnects at connectors, which can also be considered a failure if it impacts the component’s functionality.
Designing to meet the vibration requirements is important, and vibration testing is where the design will ultimately be vetted. There are many good practices that can be used in the design phase that will lead to success when it comes to the test phase. Good test setup for a vibration test is imperative to ensure the test exposes the component to the right environment, and to monitor component functionality throughout the test. Often special considerations need to be taken to ensure transient failures during vibration don’t go undetected.
Here are some ways to ensure your component design and vibration test will be successful:
As mentioned previously, one major failure mode in electronics from exposure to vibration are cracked and broken solder joints, which results in components becoming disconnected from the PCB. During the design phase an analysis can be performed to identify components that may be susceptible to this. The analysis looks at stresses in the solder joints based on component geometry, board geometry, and the vibration requirement, and identifies parts that may exceed the allowable stress limit. When those parts are identified there are a number of mitigations that can be taken.
One is to choose component packages that are better for vibration. Components in larger packages will be exposed to greater forces and consequently greater stresses during vibration. This is due to the larger package having larger mass, but also due to flexing of the PCB during vibration. So generally smaller packages are better for vibration if that is an option. Also packages that are flat on the PCB with many solder joints for attachment are better than packages that stand high on the PCB with a limited number of solder joints. Special care needs to be taken with brand new parts / packages / form factors that have not previously gone through testing.
When it’s not possible to change a part to one with a more favorable package, another mitigation that can be used is to add bonding. Bonding helps reduce the stresses in the solder joints by transferring some of the load away from the solder joint and onto the bond. Bonding can be applied in a number of ways from fay bonding underneath the part, to fillet bonding around the perimeter, to strap bonding over the top, or some combination of them all. Bonding can be extremely effective in making components more robust and able to survive vibration, but it comes at the cost of more expense in manufacturing, and more difficulty in performing reworks or repairs. The pros and cons need to be weighed for every application, but bonding is a great tool to have in the tool belt for addressing vibration concerns.
Photo by Kaspars Eglitis on Unsplash
Another design consideration for surviving vibration is chassis / housing / packaging design. For the chassis, ensure there are no features with sharp angles where stress concentrations can develop. Ensure packaging features like stand offs, PCB mounts, and component mounting features are beefy enough to handle the loads. Leveraging existing designs that have survived vibration is always a good approach when looking at detail designs of these features, but when this isn’t possible a stress analysis and development testing can help to gain confidence leading into a formal qualification test.
One final design consideration is connector selection. Connectors can be very tricky to get right, especially when vibration environments are extreme. It doesn’t take a lot of movement between connector mating halves to result in contact discontinuity, so ensure connectors have robust locking mechanisms that secure the connection in the presence of a vibration environment. Also ensure the locking mechanism can’t result in the connector backing out over long term vibration exposure, or consider connectors with features like lockwire holes or thumb screws if additional mitigations are needed. One important thing to do is to ensure harnesses are adequately secured both in the design as well as in the vibration test, since harness movement is the main source of connector movement.
Conclusion
Vibration is one of many requirements that designs need to be able to meet. McClain Electronics Engineering (MEE) has lots of experience designing components to meet severe vibration environments, and also with ensuring the vibration test is setup and performed correctly. We can help with any phase from design, test requirements and test setup development, test execution, or recovery from a test failure. With MEE you can tackle vibration and know with confidence your component will pass the test.
Let MEE know if we can help you with vibration or any other design and development needs.
Zach McClain
McClain Electronics Engineering
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