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How to Select a Coin Cell Battery Holder for Maximum Shock and Vibration, and Ease of Replacement

Source: digikey
Category: Industry C...
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文章创建人 Art Pini
2021-10-22

Original Title:How to Select a Coin Cell Battery Holder for Maximum Shock and Vibration, and Ease of Replacement

  Lithium coin cells like the CR2032 have found their way into a multitude of portable electronics applications, many of which will require battery replacement. To be end-user friendly, designers must ensure coin cells are mounted in battery holders that make battery replacement simple and fast. At the same time, the battery holder must have a robust design that maintains good connection to the cell even in the presence of shock and vibration. Cell holders must also offer safe retention of the cell and protect against inadvertent short circuits.

  On the manufacturing side, the cell mounts must be designed for automated pick-and-place production with a clear separation of connections. Cell mounting designs should be available with either surface or through-hole mounting.

  This article looks at the concept behind these battery holders, reviews their unique features and benefits, and reviews design considerations when selecting coin cell battery holders. It then introduces and shows how to apply the Snap Dragon series of coin cell holders from Memory Protection Devices (MPD) that use a non-conducting, snap-in cover to address designers’ concerns.

  The Snap Dragon concept

  To address these design requirements, MPD introduced the Snap Dragon series, a whole new category of cell holders. These greatly increase the reliability of open-top coin cell holders through the use of a locking, snap-on cover that prevents shock, vibration, and drops from dislodging the cell or causing intermittent connections. To meet the user-friendly requirement, the cover can still be removed in a “snap”, allowing for quick and easy battery replacement.

  For manufacturing, the device’s liquid crystal polymer (LCP) base is tolerant of high-temperature reflow soldering processes. The snap-in cover is not only designed for ease of use, its use of polypropylene material means it is strong and flexible enough to allow multiple battery replacements over time. Even with these features, the Snap Dragon holders keep a very low profile, typically adding only 1 millimeter (mm) to the coin cell battery above the pc board.

  Taking a closer look, the Snap Dragon coin cell battery holders use a two-piece design consisting of a snap-on battery retainer and a mating base, which together hold the cell (Figure 1).

  

Image of Snap Dragon coin cell holders


  Figure 1: Snap Dragon coin cell holders use a two-piece design consisting of a base and a snap-on, non-conductive battery retainer to ensure reliable operation even in the presence of shock and vibration. (Image source: Memory Protection Devices)

  With the cover snapped on, the coin cell is completely locked in, ensuring the Snap Dragon provides an excellent and reliable connection.

  While some high-reliability cell holders can make user battery installation and replacement difficult or impossible, the Snap Dragon cell holder is designed to offer an easy and intuitive process. The Snap Dragon design is patent pending and is the newest addition to MPD’s portfolio of battery holder technologies.

  Snap Dragon coin cell holders are available in two different sizes to fit BR/CR2032 and BR/CR1225 cells in either horizontal or vertical orientation. They can be supplied with either tabs for surface mount technology (SMT) soldering or pins for through-hole mounting on a printed circuit board. These cells offer up to approximately 220 milliamp-hours (mAh) of power and are quite small, making them perfect for circuits with low power requirements in handheld portable devices (Figure 2).

  

Image of assembled MPD Snap Dragon surface mount coin cell holder


  Figure 2: An assembled Snap Dragon surface mount coin cell holder showing the battery retainer snapped into place, holding a 20 mm coin cell to the base. (Image source: Memory Protection Devices)

  The base component

  Snap Dragon coin cell holders feature a base made of high-quality virgin liquid crystal polymer plastic, which is both thin and strong. It is also capable of withstanding the high temperatures associated with SMT soldering processes. The holder is rated for a temperature range of -40°C to 280°C. The LCP base also provides excellent chemical resistance and can withstand adverse environmental conditions.

  The Snap Dragon base is fabricated with dual pressure contacts of nickel-plated phosphor bronze with a flashed gold coating for excellent electrical conductivity. This also provides added corrosion protection when contacting the coin cell’s nickel-plated stainless-steel electrodes. The dual pressure contacts not only offer extremely low electrical resistance but also provide a snug fit to aid in preventing the coin cell from being dislocated as a result of shock, vibration, or mishandling (Figure 3).

  

Image of dual pressure contacts on an MPD surface-mount base


  Figure 3: Shown are the dual pressure contacts on an MPD surface-mount base. (Image source: Memory Protection Devices)

  The base shown in Figure 3 is a Memory Protection Devices BHSD-2032-SM. It is a horizontal oriented surface-mount base for a CR2032 coin cell. The dual pressure contacts are plainly shown.

  The Snap Dragon cell holders are able to provide all of these advantages while maintaining an extremely low profile.

  The cell retainer

  The second component of the Snap Dragon series cell holders is the translucent polypropylene (PP) cell retainer or cover that delivers reliable battery retention. Both strong and flexible, the cover’s ease of use comes from the use of pliable tabs that permit the battery retainer cover to be easily removed and reinstalled multiple times without distorting the plastic.

  The mating retainer for the base shown in Figure 3 is MPD’s BHSD-2032-COVER (Figure 4).

  

Image of matching cover for the coin cell holder base


  Figure 4: The matching cover for the coin cell holder base shown in Figure 3. (Image source: Memory Protection Devices)

  Cell holder reliability testing

  Reliability testing for the BHSD-2032-SM holder base includes swept sine vibration (10-50-10 hertz (Hz)) testing for an hour in each of the orthogonal axes with no cell dislodgement and no loss of contact continuity greater than 10 microseconds (ms). The devices are also subject to 150 g, half-sine shock testing, including three shocks in each direction on each axis for a total of 18 shock pulses with no evidence of physical damage. The final mechanical environmental test is a one-meter drop test, again with no dislodgement of the battery cell.

  All of the Snap Dragon coin cell holders have similar test specifications, providing assurance of their reliability.

  Snap Dragon configurations

  The Snap Dragon cell holders are available in a variety of configurations. The previously mentioned BHSD-2032-SM is a surface mount holder intended for horizontal installation. The BVSD-2032-PC with its retainer, the BVSD-2032-COVER, represents a vertical cell orientation using through-hole pc board mounting (Figures 5a and 5b).

  

Image of MPD BVSD-2032-PC cell holder and its retainer BVSD-2032-COVER


  Figure 5: The BVSD-2032-PC (a) is a vertically oriented cell holder using through-hole mounting, along with its retainer, the BVSD-2032-COVER (b). (Image source: Memory Protection Devices)

  The through-hole versions of the Snap Dragon cell holders use pins rather than solder pads but are otherwise identical in construction to the surface-mount versions.

  In addition to holders for 20 mm diameter coin cells, MPD includes holders for 12 mm coin cells (Figure 6); the key differentiator is the battery capacity.

  

Image of 12 mm battery cell holder (a) along with its retainer (b)


  Figure 6: A 12 mm battery cell holder (a) along with its retainer (b). (Image source: Memory Protection Devices)

  The BHSD-1225-SM (shown in Figure 6a above) is designed to accommodate BR/CR1225 coin cells and is configured for horizontal surface mounting. There is also a version available intended for through-hole mounting. They both share a common cover retainer in the BHSD-1225-COVER (b).

  Regulatory compliance and application

  For applications intended for worldwide distribution, it is important to know that the LCP plastic used in the Snap Dragon cell holders is environmentally friendly, halogen and PFOA free, and in full compliance with SVHC, REACH, RoHS, and WEEE regulations.

  The Snap Dragon family of coin cell holders is suited for compact handheld medical products and other applications where reliability, durability, and ease of use are important.

  Snap Dragon cell holders are highly compatible with various types of sterilization cycles common in medical applications. Here, its two-piece snap-on feature is especially valuable as the battery may have to be removed prior to sterilization as the sterilization cycle temperatures may exceed the battery’s maximum rating for heat exposure.

  Conclusion

  The selection and integration of battery holders requires careful consideration of the end application specifications and use model. Battery size, orientation, automated placement compatibility, regulatory compliance, and ease of battery replacement are primary concerns, along with overall cost. The Snap Dragon coin cell holders from MPD offer low-cost, reliable battery retention for BR/CR2032 and BR/CR1225 battery cells, even in the presence of drops, vibration, or shock. All while enabling easy cell replacement.


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