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Resistors

Precautions for Resistors

General in fixed resistors

  • For basic precautions of using resistors, refer to the technical report "EIAJ RCR-2121B Safety application guide for fixed resistors for use in electronic components" issued by JEITA.
  • When the resistors are operated in ambient temperature above the rated temperature, the power rating must be derated according to the derating curve.
  • Resistors in general may emit flame, fire, smoke or red heat when overload is applied.
  • Flame retardant resistors may emit smoke or cause red heat when overload is applied but unlikely to emit flame or fire.
  • When the resistors are sealed and coated by coating materials such as resin, deterioration of the resistor by thermal stress or resin may affect the characteristics. Confirm with KOA for the performance and reliability specifications in advance.
  • When the resin absorbs moisture, the resistance to moisture and corrosion of the resistor may deterorate, so be aware.
  • When the resistor is coated, potted and molded by resin materials, the curing stress could cause peeling of protective coating and crack of solder fillet, resulting the resistance change and disconnection. Do not coat nor seal the flame retardant coated resistors nor metal oxide film resistors.
  • Allow enough intervals for cooling after mounting metal film resistors, before washing the flux. Residues of ionic substances may deteriorate resistances to moisture and corrosion.
  • When a power exceeding the rated power is applied in a short time, we can not guarantee the safety only that the average power is below the rated power. Please contact KOA with the surge voltage or current waveform for advise.
  • Cylindrical film resistors have inductance due to the spiral trimming. Please be aware when using in a high frequency circuit.
  • The flame retardant resistors are weak against mechanical stress compared with the general resistors due to the special coating. Please do not apply impact, vibration or pinching with pliers or tweezers to the resistor body. Do not apply any external force to the protective coating until drying is fully completed after washing.

Chip resistor array and networks

  • Misalignment of the mounting, abnormal solder amount and the loading direction mistake of the flow soldering could cause solder bridge to the neighboring terminations.
  • Adhesive of ionic residuals on the resistor or board could cause migration between the neighboring terminations.

Fixed wirewound type resistors

  • Wirewound type resistors have inductances and parasitic capacitances resulting from the winding structure. Therefore, they could resonate when used in a high frequency circuit.

Fixed fusing resistors

  • Confirm beforehand that the overload condition of the abnormal
    situations are within the fusing area.
  • Contact KOA in advance when excess overload of the rated voltage is continuously applied, since there is a possibility of damage accumulated in the resistor.
  • The arc phenomenon may occur when high voltage is applied again
    after fusing by over current. Make sure to use the product below the maximum open circuit voltage.
  • Contact KOA about the maximum open circuit voltage for it varies
    depending on the product type and resistance.
  • The fusing characteristics could change when the resistors are coated, potted and molded by resin materials.

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