The challenge can be in the quantity of the leads required to get through a small space, because the larger the hole in the chamber, the greater the risk for leakage. Smaller, high-density feedthroughs are better than multiple hermetic connectors. Then there are the issues with mating a hermetic connector in an environment that is submerged, often the case with flywheel applications because the flywheel chambers are sometimes encased in some sort of heat transfer fluid.
Further, there is the risk of using welding to hermetically seal the feedthrough to the chamber wall—oftentimes process control issues in welding create unanticipated temperatures that damage electrical feedthroughs.
MASS SPECTROMETRY
An interesting example of the potential impact of a feedthrough on final product design can be seen in the case of mass spectrometers, which require high voltage (up to 30kV) to be carried into a vacuum chamber. In one instance, the only off-the-shelf solution was approximately 1.5” in diameter and anywhere from 5-10” long on either side of the chamber wall. Given that the equipment was being designed as a bench-top unit, this would have tripled the overall size of the unit, and the space needed to accommodate the feedthrough would have possibly prevented the unit from even functioning to the required specifications.
Starting from scratch, a custom solution was created that was only 5/8” in diameter and 1” on either side, satisfying the envelope requirements and including the pre-installed O-ring and snap ring. In addition, the feedthrough was QC prequalified for continuity and vacuum sealing so that the feedthroughs could be supplied directly to manufacturing for installation without having to go through the internal QC process. This value-added service increased the efficiency of the production process significantly.
A/C COMPRESSORS
With intense price pressures placing a premium on component and manufacturing costs, the challenge of replacing a substandard solution for a feedthrough in the compressors used in residential air conditioning units was extreme. A manufacturer was experiencing failures in the glass-to-metal feedthroughs used for power after the unit became encased in ice and snow with subsequent melting.
The freeze/thaw cycle induced a potentially dangerous “venting” problem in which the leaking part would sometimes “launch” a pin or series of pins out of the compressor, followed by a flammable mixture of oil and gases. A hermetic feedthrough can’t vent in the traditional sense, and it also allows for the immediate integration of additional components inside of the compressor to achieve much higher levels of efficiency.
On the component side, a custom solution was developed that eliminates this failure point with a better-designed feedthrough constructed with the proper materials. On the cost side, the solution is not only competitive on a per-piece basis, it adds considerable value by reducing assembly time with the pre-stripped, pre-tinned, and labeled wires and connectors for easy installation, plus it can be supplied as an integrated part of existing components, further simplifying the supply chain and enhancing value to the customer.
SEMICONDUCTOR MANUFACTURING
The attention to detail needed for semiconductor manufacturing at the micro level is impressive, but the macro level of manufacturing equipment and processing can’t be overlooked. With intense focus on the end product, and an incredibly competitive market, any efficiency or reliability to be gained in the manufacturing process can pay big dividends.
In the case of one new piece of manufacturing equipment, the overall design led to the need for a feedthrough that had a 90° bend with less than a ½” radius. Another design required a feedthrough with an oval housing. Both of these design requirements eliminated the possibility of finding an off-the-shelf solution. Instead, they necessitated a one-off housing design to satisfy the requirements without redesigning a significant portion of the unit. Unless a supplier specializes in designing and manufacturing customized feedthroughs, these sorts of solutions often entail high tooling and setup costs and long lead times. It’s important to shop around for a solution that not only meets your project’s design needs, but also satisfies your cost and delivery expectations.
LEAD-FREE SOLDERING OVENS
With the introduction of the RoHS standards, electronics manufacturers need to have ovens capable of melting the compliant solder in a nitrogen purged atmosphere and at a higher temperature than traditional solders. One manufacturer of these reflow ovens was seeing both excessive nitrogen consumption and unacceptably high power usage in its first production run.
Upon investigation, the issue was traced to a wire penetration in the oven wall that had been sealed in-house with RTV silicone during manufacturing. Nitrogen was found to be escaping through the wire windings in the penetration, carrying away large amounts of heat and nitrogen. A customized feedthrough developed to hermetically seal the penetration ensured that subsequent versions of the oven performed to specifications.
Samples of feedthroughs are shown in Fig. 1, Fig. 2, Fig. 3, and Fig. 4.
CONCLUSION
Whoever coined the phrase “Don’t sweat the small stuff,” was more than likely not an engineer. Because, when you get right down to it, everything engineers do is ultimately defined by the success of “the small stuff” that comprises the larger design projects they tackle.
Although the examples provided here are based on personal experience with feedthroughs, the concept is universally applicable. No matter how small, or seemingly insignificant the detail, failure to incorporate the best solution for any given application can result in production delays, cost-overruns, frustration, and, in the worst-case scenario, catastrophic failure.
Most vendors of components and subassemblies will be happy to provide input during the design stage to help you avoid such issues. If your supplier is unable to provide a solution that meets your needs, your budget and your delivery timetable, you may want to consider working with one who is. Chances are they’re well aware of how important the small stuff really is.