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Thermal management keeps pace with fast processing

A Southco product story
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Edited by the Electronicstalk editorial team Sep 13, 2007

The method of heat sink attachment can be crucial to the performance of the system.

Incorporating increasing processing power into shrinking electronic components and tighter PC board layouts is creating new thermal management concerns for designers of computing equipment and other electronic devices.

Heat sink devices are one method used to transfer heat away but according to Nick Bennett, Engineering Manager of Southco, careful consideration has to be given to their method of attachment.

According to industry data, the trend in the heat load per product footprint has grown tenfold for server and communications applications over the past decade, and it is projected to go even higher.

This makes thermal transfer a more crucial aspect of electronics design.

Mechanical heat-sink devices, featuring a fin design with a high surface area to footprint ratio, are one method used to transfer heat away from electronic components but the attachment option chosen for their installation could have a significant impact on the efficiency of the thermal management design.

In order to optimise the heat transfer performance between microprocessor and heat sink assemblies it is essential to maintain a consistent fastening.

Each available attachment approach comes with its own advantages and disadvantages in terms of size, cost, complexity and thermal effectiveness.

How well each translates into performance in the intended application can be affected by other considerations including operating conditions such as shock or vibration.

Changes in mounting hardware, tolerance differences among various components, or lack of attention during the assembly process could all affect the efficiency of thermal transfer performance in the ultimate real-world application.

Some of the simpler designs offer obvious advantages in terms of low cost, but can incur problems in more demanding applications.

As the size of the heat sink increases, withstanding shock or vibration can become more challenging.

Equally, the use of double-sided tape or adhesive compounds can be difficult to implement in the manufacturing environment and can compromise the performance efficiency of the heat sink.

Plastic clips are another low-cost alternative but again reliability can be challenged by shock, vibration or heat sink weight.

Retaining clips provide for easier heat-sink replacement, but reliability has been shown to vary during shock testing and they can require removal of the centre fin material on the heat sink, where most of the heat is typically absorbed.

Other mechanical fastening options that provide better tolerance to shock, vibration and alignment include a variety of screw, pin and spring attachments.

These include both loose and captive hardware designs.

Captive designs help to avoid problems with loose hardware posing potential short-circuit problems on printed circuit boards.

They can also simplify screw alignment for easier assembly even in crowded compact PCB layouts.

The final point to consider when specifying heat-sink mounting hardware is that maintaining proper heat-sink alignment and contact across the full surface of the chip or other heat-generating electronic device is a key to good, consistent thermal transfer.

Compressible heat-transfer pads can help to maintain thermal transfer performance while compensating for uneven surfaces or for inconsistencies in mounting pressures.

Spring-loaded self-levelling heat-sink fastening hardware that maintains consistent pressure across the surface of the heat-generating component, and automatically adjusts to compensate for thermal expansion, also helps to improve thermal transfer performance, used either with or without compressible pads.

In terms of overall product design, the choice of fastening method for the heat sink device may seem to be somewhat peripheral.

However, as applications become more demanding it is such points of detail that can make or break product performance.

The advice is to consider the question of heat-sink attachment as an integral part of the design process - and consult specialist fastener manufacturers who offer fastener options specifically designed to accommodate a broader range of demands in heat sink applications.

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