Many suppliers have recently introduced chip resistors with higher power ratings for a given chip size. In some cases, these smaller components can be used to reduce the overall size of the circuit. However this opportunity for size reduction also brings the need for caution on the part of the design engineer.
The above temperature rise vs. % rated power graph illustrates one of the challenges faced by circuit designers. Stackpole recommends that film chip resistors, have their film temperature kept under 105°C . The data shows that the chip sizes 1210 and larger at full rated power and on a PCB built to minimum standards may have difficulty with this. These larger chip sizes require some type of thermal reduction techniques to be used. Some common techniques include: using multiple layers in the board, using heavier copper per layer, larger solder pads or lands beneath the solder pad windows, via through the terminations, and airflow. These same techniques must be employed when circuit designs are downsized especially when using larger, high power resistors.
Most high power chip resistors have essentially the same materials in the same relative amounts as their standard power counterparts of the same size. Typically, the main difference is that the film itself is designed to handle the higher temperatures associated with using chip resistors at high power. Even though you may be able to replace all 0603's with high power 0402's, it isn't wise to take that space savings and pack the circuit layout proportionally closer together. Even though both parts are rated for use at 0.1W, the high power 0402 will run hotter at that power level than the standard 0603.
While engineers need to be careful about how small they shrink their designs that have heat generating components such as resistors, they can utilize that saved space with other components that don't generate additional heat.
The RHC2512 series from Stackpole is more thermally efficient than other high power 2512 thick film chip resistors. The RHC uses different materials, design, and processing to significantly lower PCB temperatures by more effectively dissipating the heat both into the board and into the ambient air. The RHC2512 typically yields lower resistor temperatures due to self-heating of 30°C . Smaller chip sizes are currently under development.
As long as resistor temperatures are kept below 105°C, high power resistors can be an effective way to downsize or to add functionality to circuit designs.
More information and datasheets available at: www.seielect.com
For more information about Stackpole products, contact Stackpole Electronics, Inc. at
Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now part of the Akahane Stackpole Manufacturing Group (ASMG), Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Shenzhen and Japan; and international sales offices in Tokyo, Taipei, London, Hong Kong and Shenzhen.