Design of coin-cell battery holders for miniature handheld medical devices

Design of coin-cell battery holders for miniature handheld medical devices

The battery holder design plays a critical role in handheld medical device performance and reliability, helping minimize its size and weight to make it smaller and more streamlined

By Thomas Blaha
President, Memory Protection Devices

Handheld medical devices face numerous hurdles on the way to market. First, they need to obtain FDA 510(K) pre-marketing approval for safety and effectiveness.Then, they must be manufactured to the highest quality standards using superior grade components to ensure long term reliability and greater customer satisfaction. All phases of product design are critical, including the selectio of the battery holder. Often considered an afterthought, the battery holder plays a central role in product performance and reliability. For example, the choice of battery holder can help minimize size and weight to make the device more streamlined and miniaturized. The ideal battery holder can also enhance product ruggedness to better survive normal wear-and-tear as well as the extreme abuse of being dropped and manhandled, all the while maintaining a strong electrical connection that serves as the lifeblood of the device.

For decades, coin cell batteries primarily sat flat on the PCB along with the other various components. However, as handheld devices have become increasingly miniaturized, a large diameter battery begins to take up a disproportionately large surface area. Radical rethinking was needed – not of how a battery should sit on a PCB, but of where a battery should sit in a PCB. As a result, vertically-oriented coin cell holders were introduced, giving product designers a choice between making the medical device wider or thicker. To further minimize the height of vertically-oriented coin cell holders, a new option emerged, whereby a small hole was drilled in the surface of the PCB, thus allowing the battery holder to sit partially through instead of on the PCB, helping to reduce overall height. The same concept is now being applied to horizontal coin cell holders. This new style of battery holder works as both structed with gold plating over nickel over copper plating over a phosphor bronze base. The nonreactive nature of gold makes gold-plated contacts more resilient to the corrosive effects of multiple sterilization cycles. Use of gold plating also helps prevent corrosion problems associated with bi-metallic contact, as well as temperature and humidity during shipping and storage.

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