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Heat Sink - o - de Mayo  by Matt Stevenson, Sunstone Engineer

As electronics get smaller, faster and more powerful the heat generation of these components grow in a variety of ways. In terms of a PCB, heat can be generated, reflected or increased from several different factors. Some of the more common factors are power consumption, emissivity, materials, internal heat conduction and external heat conduction. Heat, if not dissipated quickly and effectively, can result in overheating and a number of failure modes in an electronic design. 

The main materials used in PCBs (copper and epoxy laminates) work very well from an electrical performance standpoint but leave a lot to be desired in terms of heat dissipation. There are ways that the layout and design of the PCB can help mitigate heat issues and give you a more forgiving design. Here are a few of the considerations that can be implemented during the design phase to help. 

• Analyze the components used for their heat generation ability.
• Plan for external cooling (air flow, positioning / orientation in the device, heat sinking, liquid cooling etc.) In general, air flow is one of the most effective cooling options in an electronic assembly and the path of air flow is very important to consider.
• Place the highest heat generators in positions on the PCB with the most opportunity for dissipation, avoid the edges of the board and make sure there is adequate spacing to other components unless there is a direct heat sink planned.
• Spread out the high heat generators across the PCB to increase the opportunity for dissipation.
• Keep the heat sensitive parts isolated from the heat generators. Placing them on the opposite side of the PCB (away from any heat sinks directly under these heat generating parts) helps by taking advantage of the poor thermal transfer properties of the PCB laminate materials.
• Techniques using via holes, thicker copper, thinner laminates and other localized sinking can drastically improve dissipation.(see PCB007 article pg. 42 “New landing design to reduce Thermal Pad Failures” for effective techniques).

In general, make sure you know where your heat is coming from and that you have a plan for dealing with it so your device will live a long and prosperous life, as intended.