PCBA Tech - What are the different requirements for varistors in PCBA design

What are the different requirements for varistors in PCBA design
What are the requirements for varistors in PCBA design?
1. Use temperature/storage temperature:
Keep the working temperature of the paste circuit within the working temperature range indicated on the product specification. After mounting, the storage temperature when the circuit is not working is kept within the operating temperature range indicated in the product specification. Do not use at high temperatures exceeding the specified maximum use temperature.

2. Use voltage

Keep the voltage applied between the terminals of the varistor below the maximum allowable circuit voltage. If used incorrectly, it will cause product failure, short circuit, and heat generation. The operating voltage is below the rated voltage, but when using it in a circuit where high-frequency voltage or pulse voltage is continuously applied, be sure to fully study the reliability of the varistor.

Third, the component heats up

The surface temperature of the varistor should be kept below the maximum operating temperature specified in the product specification (the temperature rise caused by the self-heating of the component should be considered). The temperature rise of the varistor caused by the use circuit conditions, please confirm in the actual operating state of the equipment.

Fourth, the use of place restrictions, varistor can not be used in the following places:

4.1 Places with water or salt water;

4.2 Places prone to condensation;

4.3 Places with corrosive gases (hydrogen sulfide, sulfurous acid, ammonia, etc.);
4.4 The vibration or shock conditions of the place of use shall not exceed the range specified in the product specification;

Five, circuit board selection

The performance of the alumina circuit board may be deteriorated due to thermal shock (temperature cycling). It is necessary to confirm whether the circuit board has any influence on the product quantity when using it.

6. Setting of pad size

The more the amount of soldering, the greater the pressure that the varistor will experience, and will cause quality problems such as surface cracks on the component. Therefore, when designing the circuit board pad, the appropriate shape and size must be set according to the amount of soldering.

When designing, keep the size of the pad equal to the left and right. If the amount of solder on the left and right pads is different, the solidification of the one with the larger amount of solder will be delayed when the solder is cooled, and the other side may be stressed and cause cracks in the part.

Seven, the configuration of parts

After the varistor is soldered and installed on the circuit board, or the circuit board is bent during operation, the varistor may be broken. Therefore, the bending strength of the circuit board should be fully considered when configuring the components, and excessive pressure should not be applied.
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