Introducing our New Series: the Silent Failures of Electronics
When we think of product failures, we typically think of the catastrophic ways a product would break: mechanical shock, liquid spills, or battery fires. As product designers, we don’t always consider the product degradation that creeps up over time, the silent failures of electronics and their cooling solutions that keep them running. This new Silent Failure Series explores how products can slowly deteriorate and break right under our noses and some of the ways we can address those issues. We’ll start our series with fan bearing failure and its impact on thermals and product design.
Silent Failure: Fan Bearing Failure
Higher powered thermal management solutions typically utilize forced convection. This generally requires the use of a blower or a fan. Heat sinks and fans are like the peanut butter and jelly of electronics. You can use each by themselves, but they complement and amplify each other’s’ effects when used in conjunction. If fans work so well with heat sinks, why would you ever consider not having them in your thermal management solution?
Unfortunately, fans and blowers have a few drawbacks. First it’s an electrical component. Electrical components have many failure modes, but fans are also mechanical in nature. Engineers designing the board may not be as familiar with the various mechanical failures fans introduce to the system and don’t take the necessary precautions during the design phase.
The silent failure with fans or blowers is the degradation of bearings. Over time, the bearings within the fan start to break down due to the mechanical wear and friction between the components. The fan motor then works harder to rotate the impeller within the bearings which no longer allow the smooth rotation they used to. This failure mode is the least silent of our failures. Users may notice the noise from the fan slowly changing over time, but may be so gradual that they might not be alerted to a change in performance.
Fan bearing failure may not seem like a big deal. The fan may still function and rotate. But if the bearings inhibit the fan’s functionality enough, the fan can’t move as much air as it used to. Then it’s no longer able to transport enough air to cool the electronics to a safe operating temperature. Electronics that spend too much time above this threshold start to degrade and fail. Ineffective fans leads to unexpected product failures and unhappy customers.
Designing around Fan Failures
The good news is that engineers have a few ways of mitigating the silent failure of deteriorating fan bearings.
The best way to address this sort of silent failure is to not use fans at all. Natural convection is more reliable than forced convection solutions since it relies on buoyancy and gravity for heat transfer. At least, we certainly expect that gravity is going to last much longer than any fan bearings we currently produce. Either way, natural convection solutions don’t utilize any moving parts, so it removes frictional breakdown from the equation.
For higher power applications, natural convection isn’t an option. Designers create electronics to accomplish high level processing in compact form factors where there is not enough volume to stuff all the surface area a natural convection heat sink would require.
Bearing Longer Product Lifetimes with Better Fans
In cases where engineers require fans or blowers, they can use ones manufactured with a lifespan longer than the lifetime of the overall product. This generally means selecting fans with bearings designed for extended use. Products with longer expected lifetimes should shy away from fans with less expensive sleeve bearings and focus on getting either high quality double ball bearings or spring for more expensive fluid dynamic bearings. All of these fans are susceptible to bearing failure, so designers should take the time to select the right fan and consider how their product can accommodate the inevitability of bearing failure.
I Sense a Disturbance in the [Fan] Force…
One way product designers manage bearing failure is to utilize fans with diagnostic feedback signals like a rotation sensor. This helps the fan inform the product’s electronics if the fan is rotating at the speed it needs to. Then the product’s software would be able to cut back processing speed to decrease the amount of heat it’s generating. If the product has a user interface, programmers could also send a signal to users to check on the fan.
Another way to circumvent fan failure is to design your product for regular fan replacements and implement a maintenance schedule for your consumers. We all know how well users comply with regular maintenance: it can be hit or miss depending on the application and the dedication the end user has for performance. While you can expect life saving products getting regular care, a PC could have a dedicated gamer or a casual user so it may be difficult to ensure your product will get the maintenance it requires.
Fan-cy That, We Really Can Manage Silent Failures
In whichever method you choose to use fans in your product, it’s critical to take some time to consider the impact of fan lifetime and bearing degradation has on your product’s performance. Don’t let fan bearing failure cause your users unnecessary grief.
Scrutinize the choice between natural convection and forced convection solutions before committing to a fan in your product. Determine the minimum bearing quality and fan lifetime your system requires. Spend time designing in safety either with smart programming or over designing your heat sink for lowered fan performance. Consider if your users would manage adequate maintenance.
Time spent during the design phase of your product development evaluating fans can save you and your company time and costs in the long run. Aavid Engineers are experts in thermal management design and can help guide you when implementing fans in your product. Feel free to contact them with your questions on fan design and integration.