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Page: 10/13

Pulse Withstanding Chip Resistors (PWR) Application & Soldering Notes

Today's electronic devices are becoming smaller and smaller. The requirement, in particular, for pulse

withstand capability is growing due to the need to protect sensitive modern electronic systems.

To meet this demand Token Electronics have designed a Pulse Withstanding Chip Resistor (PWR

Series). The enhanced performance of the chips is made possible by the precise use of the best

resistance inks and a closely controlled production process.

Application Notes:

 Applications vary from line protection for telecommunications to surge withstanding resistors for use in

circuit breakers. Details of a typical telecomm and power supply application are given below.

 Telephone lines can be subjected to a large range of voltage disturbances, many of which can damage

switching equipment. This has led to the need for circuit protection against both high voltage transients,

usually of short duration caused by lighting strikes and overloads of longer duration, due to direct

connection to mains power lines.

 These two faults are separated into primary and secondary protection.

1.

Primary protection handles the high voltage transients, and is usually located within the exchange.

2.

Secondary protection is usually built into the equipment to be protected, and deals with both current and

voltage limiting.

 Voltage limiting prevents damage to the equipment and shock hazards, and current limiting prevents

damage to wiring.

 To determine the suitability of a (PWR) series chip resistors for your application refer to the pulse

withstanding data as given lighting surge performance using both 1.2/50μs and 10/700μs pulse shapes.

Soldering Notes:

 Electrical connection to a ceramic substrate or to a printed circuit board can be made by

reflow or wave soldering of wrap-around terminations.

 Wrap-around terminations provide good leach properties and ensure reliable contact.

 Due to the robust construction, the (PWR) can be immersed in the solder bath for 30 seconds at 260℃.

 This enables the resistor to be mounted on one side of a printed circuit board and wire-leaded components

applied on the other side.

 (PWR) resistors themselves can operate at a maximum temperature of 155℃.

 For soldered resistors, the joint temperature should not exceed 110℃.

 This condition is met when the stated power levels at 70℃ and recommended pad and trace areas are

used.

 Allowance should be made if smaller areas of copper are used.