When faced with the task of cooling a heavily populated PCB, most designers recognize the value of fans and heat sinks. Most designers also understand that more airflow (i.e. high LFM air speeds) over the heat sinks improves their cooling performance. However, many don’t realize the importance of managing how the air flows across the PCB.
Without proper management of airflow, heat sinks located far away from the fans may not be exposed to sufficiently strong airstreams. When that happens, heat sinks typically don’t cool effectively and components can overheat. On densely populated boards, proper airflow management requires selection of heat sinks that produce low pressure drop and thereby maintain high enough levels of airflow for the heat sinks downstream.
With conventional heat sinks, designing for low press drop has typically meant increasing the spacing between fins to let air pass through more easily. Unfortunately, that change sacrifices surface area, which reduces a heat sink’s cooling ability. As a result, the requirements for both low pressure drop and substantial cooling power are conflicting.
This design conflict cannot be resolved with traditional heat sinks with their vertically oriented fins. However, a unique heat sink design from Cool Innovations uses a slanted fin structure to solve the problem. The new splayed pin fin heat sinks feature an array of pins in which the outer pins are splayed away from the inner pins. This design increases the spacing between pins without reducing the heat sinks’ surface area. On heavily populated boards, use of splayed pin fin heat sinks can provide the lower pressure drop needed for proper airflow and yet still provide sufficient cooling to the many heat generating devices.
Cooling electronic components using natural convection (still air) is considerably more challenging than forced air cooling. That’s because the thermal resistance of a heat sink may be up to 20% higher in a natural convection environment than in a high-airspeed environment.
With forced air cooling, the fast-moving air breaks up the insulating boundary layers of still air surrounding the heat sink. But when there’s no airflow, the heat sink depends solely on the “chimney effect” to break these layers of still air. As a result, natural convection cooling is inherently less effective than forced air cooling.
Nevertheless, it’s possible to improve the effectiveness of natural convection cooling by optimizing heat sink design to accelerate the chimney effect. To do so, the heat sink designer must meet two goals: minimize the friction between the heat sink’s metal surfaces and the air, and maintain enough surface area for adequate heat transfer. Unfortunately, these two design objectives conflict because greater surface area in a heat sink typically leads to greater friction.
The flared pin fin heat sink represents a unique cooling alternative that was specifically optimized for natural convection cooling. A flared pin fin heat sink shares many of the advantages that a standard pin fin heat sink (one with vertically oriented pins) offers versus other heat sink styles.
A standard pin fin heat sink features round, smooth fins that lower the friction between air and fins, an omnidirectional structure that allows air to enter and exit the heat sink from all directions for better cooling, and fabrication from an aluminum alloy with higher thermal conductivity than standard heat sink materials.
But unlike a standard pin fin heat sink with its vertically oriented pins, a flared pin fin heat sink features an array of pins that are bent gradually outward. This bending of the pins widens the spacing between them significantly without sacrificing any surface area. And so, the flared pin fin design overcomes the main challenge of natural convection cooling by resolving the conflicting demands for high surface area and low friction between heat sink and air.
Our customers bear the responsibility for testing Cool Innovations' products for any proposed use. Any information provided by Cool Innovations Inc. is believed to be accurate, but our customers must accept all responsibility for use and applications of Cool Innovations Inc. products. Our products are sold without warranty, whether expressed or implied, as to the suitability, merchantability or fitness of any proposed application. Cool Innovations Inc. shall not be liable for incidental or consequential damages whatsoever.