Breakthrough technologies often make headlines, and components such as button cell cases are often overlooked, although they play an important role in supporting the attention of button cells. Battery packs may fail due to vibration, heat, shock, moisture, and corrosion, and design engineers face increasing challenges when developing power management solutions to address these real-world issues. By focusing on the following criteria, engineers are able to achieve product reliability at the most appropriate cost.
Button battery retention and disassembly
A well-designed button battery case must resist shock and vibration while maintaining sufficient flexibility for convenient battery replacement. Unfortunately, these standards are often contradictory, because better retention is more difficult to disassemble. Look for a battery case that has a convenient battery removal function.
It is especially important to test the battery pack in the field. If the button battery case is in your hand, rather than soldered to the printed circuit board and surrounded by other components and housings, the battery removal is usually much easier.
Durability
The durability of the battery pack is especially important for applications that may require frequent battery replacement during the life expectancy of the product. This problem is further exacerbated if the battery case uses a high fixture due to increased wear during battery insertion and removal. If your application requires relatively frequent battery replacement, look for the number of cycles that have been tested for this battery pack.
All battery compartments should be polarity protected so that they do not touch when the battery is incorrectly inserted. This is even more important if it is expected to require multiple battery replacements.
Conductivity and corrosion resistance
Exposure to overheated and excessively humid environments, corrosive chemicals, or airborne contaminants can often cause problems associated with corrosion build-up, which can negatively impact electrical performance. To minimize these effects, choose a battery case made of corrosion-resistant materials. The presence of metals with different electrochemical properties may further exacerbate the corrosion problem, resulting in galvanic corrosion. By using insulators or gold plating, the effects of these effects can be minimized.
Metals with good electrical conductivity, such as gold, may have unexpected additional advantages. They have less friction, which reduces the force of insertion. Although the shape of the outer casing and contacts is the main source of strength during insertion, gold and similar materials require less force than tin and copper when all other factors are the same.
Required tolerance
Even for batteries with comparable performance, the size specifications can vary widely. For example, according to industry standards, the height of the CR2032 coin cell may vary from ±0.3 mm or 10% of the total height. Therefore, it is critical that the button battery case can adapt to normal height changes without accepting an incompatible battery. A loose connection is unacceptable because it can damage electrical performance.
If the battery is factory installed and the designer is able to control the battery used, then the problem is less serious, but if the end user can purchase a replacement battery, then it should support the full range of battery sizes.
Solderability requirements
The soldering process also affects the choice of button battery compartments. For example, button cell cartridges that require SMT soldering should be made of high quality LCP plastic that provides superior dielectric strength at high temperatures and can withstand the high temperatures of a 300 °C lead-free reflow soldering process. In contrast, the wave soldering process requires a lower strength material to enable the use of PBT/Nylon plastic insulation. This material provides 5 s to 560 V/mil dielectric strength at 25 ° C. It is resistant to chemicals and solvents, operates over a wide temperature range, has excellent thermal cycling performance, and has a minimum of 5000 MΩ. Insulation resistance.
Incorrect selection of manufacturing process materials can result in many line rejections. Comprehensive product test data should be required to ensure that the button battery case meets or exceeds the ANSI/EIA-5405000 standard and that all raw materials used are of good quality.
Production integration
When designing products for high volume production, button battery packs should be supplied to the pick and place line using a standardized tape and reel package. In addition, applicable government or industrial management conformance requirements, such as RoHS and lead-free requirements, should also be considered.
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