Rev Date: 10/8/2021

3

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BR Series

Bare Element Current Sensing Resistor

Stackpole Electronics, Inc.

Resistive Product Solutions

High Power Chip Resistors and Thermal Management

Stackpole has developed several surface mount resistor series in addition to our current sense resistors, which have had higher power

ratings than standard resistor chips. This has caused some uncertainty and even confusion by users as to how to reliably use these

resistors at the higher power ratings in their designs.

The data sheets for the RHC, RMCP, RNCP, CSR, CSRN, CSRF, CSS, and CSSH state that the rated power assumes an ambient

temperature of no more than 100°C for the CSS / CSSH series and 70°C for all other high power resistor series. In addition, IPC and

UL best practices dictate that the combined temperature on any resistor due to power dissipated and ambient air shall be no more than

105°C. At first glance this wouldn’t seem too difficult, however the graph below shows typical heat rise for the CSR ½ 100 milliohm at

full rated power. The heat rise for the RMCP and RNCP would be similar. The RHC with its unique materials, design, and processes

would have less heat rise and therefore would be easier to implement for any given customer.

The 102°C heat rise shown here would indicate there will be additional thermal reduction techniques needed to keep this part under

105°C total hot spot temperature if this part is to be used at 0.75 watts of power. However, this same part at the usual power rating for

this size would have a heat rise of around 72°C. This additional heat rise may be dealt with using wider conductor traces, larger solder

pads and land patterns under the solder mask, heavier copper in the conductors, via through PCB, air movement, and heat sinks,

among many other techniques. Because of the variety of methods customers can use to lower the effective heat rise of the circuit,

Recommended Lead Free Resistor Reflow Profile