Rising power dissipations at the device and board levels continue to create more challenging thermal management problems in many applications. While heatsources are becoming more concentrated, pc boards are growing more densely populated. Naturally, these trends have put the onus on heatsinks to do a better job of transferring heat away from the semiconductors that they cool. Consequently, heatsink designs have evolved from the low-aspect-ratio, extruded aluminum heatsinks of yesterday to a wider array of options to deal with higher power levels.
Comparing different styles of heatsinks is a tricky business. Designers may look for a certain level of heatsink performance in their applications based on their power dissipation levels, ambient temperature, and allowable junction temperature. Those factors help the designer to determine the value of thermal resistance in degrees Celsius per watt that will be needed in their application. That requirement alone leaves them with a variety of options.
However, heatsink requirements become more focused, and more complex, as the designer factors in other constraints. For example, the space available in the application determines the possible heatsink volume. Another consideration is the designer's options for forced-convection versus natural-convection cooling. Even within a single heatsink style, performance can vary widely with different rates of airflow and depending on whether the airflow will be ducted (channeled) or nonducted.
The problem expands further when the same assembly contains multiple heat-generating or heat-sensitive components. Heatsink requirements will need to reflect the power being dissipated at both the component and board levels. Add to these requirements the many mechanical concerns, such as heatsink weight and method of attachment—two considerations that must take into account shock and vibration requirements—and other packaging details. Additional environmental factors like altitude also make an impact on heatsink performance.
Then there's reliability, which contributes to almost every aspect of heatsink selection. The temperature of the components affects their reliability in accordance with Arrhenius' Law: For every 10ºC drop in junction temperature, device reliability doubles. The reliability of the attachment method and thermal interface materials (how the heatsink gets assembled in production) also affects reliability. The reliance on forced-air cooling, which is of course influenced by heatsink design, adds the fan to the list of potential risk factors.
As with all engineering decisions, cost looms large. That differs from one heatsink style to another, from low to high volume, and from standard product type to custom. Tooling charges vary, depending on the type of heatsink selected. Keep in mind that the process in which the heatsink is fabricated, such as die casting, extruding, bonding, brazing, or machining, determines not just the heatsink's cost, but also the vendor's ability to optimize the heatsink to the user's specifications.
The designer must weigh all of these concerns when evaluating different types of heatsinks for the application at hand. Unfortunately, making an apples-to-apples comparison from one heatsink style to another, on paper, is bound to be difficult because heatsink vendors don't obtain their datasheet specifications under the same test conditions.
Moreover, these conditions may not resemble the conditions present in the application. Ultimately, some testing of the heatsink in the application will be in order, a task that may be mitigated by intelligent thermal modeling of the design. So choosing a heatsink isn't a trivial task. It must be considered as simply one step within a well thought out thermal management scheme.
In fact, thermal management starts well before the heatsink design. Hardware and software optimization can minimize power dissipation. Careful pc-board layout can reduce cooling re- quirements. Designers with experience in thermal management can address these concerns early in a project, perhaps sparing the need for an expensive high-performance heatsink in lieu of a smaller, lower-cost component.
For customers lacking this experience within their own companies, there are thermal management experts within the heatsink industry who can help engineers optimize their thermal designs, rather than simply selling them a thermal fix. So, a customer's experience in thermal management may influence the choice of a heatsink technology and the selection of a supplier.
Rising power dissipations at the device and board levels continue to create more challenging thermal management problems in many applications. While heatsources are becoming more concentrated, pc boards are growing more densely populated. Naturally, these trends have put the onus on heatsinks to do a better job of transferring heat away from the semiconductors that they cool. Consequently, heatsink designs have evolved from the low-aspect-ratio, extruded aluminum heatsinks of yesterday to a wider array of options to deal with higher power levels.
Comparing different styles of heatsinks is a tricky business. Designers may look for a certain level of heatsink performance in their applications based on their power dissipation levels, ambient temperature, and allowable junction temperature. Those factors help the designer to determine the value of thermal resistance in degrees Celsius per watt that will be needed in their application. That requirement alone leaves them with a variety of options.
However, heatsink requirements become more focused, and more complex, as the designer factors in other constraints. For example, the space available in the application determines the possible heatsink volume. Another consideration is the designer's options for forced-convection versus natural-convection cooling. Even within a single heatsink style, performance can vary widely with different rates of airflow and depending on whether the airflow will be ducted (channeled) or nonducted.
The problem expands further when the same assembly contains multiple heat-generating or heat-sensitive components. Heatsink requirements will need to reflect the power being dissipated at both the component and board levels. Add to these requirements the many mechanical concerns, such as heatsink weight and method of attachment—two considerations that must take into account shock and vibration requirements—and other packaging details. Additional environmental factors like altitude also make an impact on heatsink performance.
Then there's reliability, which contributes to almost every aspect of heatsink selection. The temperature of the components affects their reliability in accordance with Arrhenius' Law: For every 10ºC drop in junction temperature, device reliability doubles. The reliability of the attachment method and thermal interface materials (how the heatsink gets assembled in production) also affects reliability. The reliance on forced-air cooling, which is of course influenced by heatsink design, adds the fan to the list of potential risk factors.
As with all engineering decisions, cost looms large. That differs from one heatsink style to another, from low to high volume, and from standard product type to custom. Tooling charges vary, depending on the type of heatsink selected. Keep in mind that the process in which the heatsink is fabricated, such as die casting, extruding, bonding, brazing, or machining, determines not just the heatsink's cost, but also the vendor's ability to optimize the heatsink to the user's specifications.
The designer must weigh all of these concerns when evaluating different types of heatsinks for the application at hand. Unfortunately, making an apples-to-apples comparison from one heatsink style to another, on paper, is bound to be difficult because heatsink vendors don't obtain their datasheet specifications under the same test conditions.
Moreover, these conditions may not resemble the conditions present in the application. Ultimately, some testing of the heatsink in the application will be in order, a task that may be mitigated by intelligent thermal modeling of the design. So choosing a heatsink isn't a trivial task. It must be considered as simply one step within a well thought out thermal management scheme.
In fact, thermal management starts well before the heatsink design. Hardware and software optimization can minimize power dissipation. Careful pc-board layout can reduce cooling re- quirements. Designers with experience in thermal management can address these concerns early in a project, perhaps sparing the need for an expensive high-performance heatsink in lieu of a smaller, lower-cost component.
For customers lacking this experience within their own companies, there are thermal management experts within the heatsink industry who can help engineers optimize their thermal designs, rather than simply selling them a thermal fix. So, a customer's experience in thermal management may influence the choice of a heatsink technology and the selection of a supplier.