Several methods for implementing heat management in a PCB layout have been developed, ranging from simple cooling fans to elaborate enclosure and heat sink designs. The goal is to reduce device temperature below levels where a component might fail or a user might come into contact with extreme temperatures. In many PCBs where form factor is not a challenge, high temperature components are normally targeted with a fan or heatsink.
When there is no room for a fan or heatsink, what can be done to remove heat from a high-temperature component? Heat management options might need to be applied in the assembly or in the internal layers of the board with embedded copper structures. Most designers know about embedded copper in terms of thermal vias, but more aggressive options involve a press-fit copper structure that provides higher thermal conductance.
Comparison of Heat Management Options
The table below shows a brief comparison of thermal management options that can be implemented in a PCB layout and in an assembly. Some of these options require designing something into the board directly, while others are added to the final assembly or enclosure.
Embedded Copper Structures
Embedded copper structures are small or large bits of copper that can transfer heat through the stackup. Thermal vias are the classic type of embedded copper structure that transfers heat to an internal plane or a heat sink on the opposite side of a board (or both).
Lower power devices will sometimes have a single component that generates most of the heat in the system, and it will be fine to target this component with a single thermal management technique. For SMD integrated circuits, this will most likely be a set of thermal vias that are connected to a thermal pad on the surface layer. This can then be soldered directly to a grounded die-attached pad on the component package.
Component footprint with four thermal vias.
For components that output much greater power, or that do not have much room for a die-attached pad, some other method is needed to remove heat. The classic approach is to place a heatsink and fan, such as would be done with a CPU or GPU. In smaller devices like smartphones, another strategy is to bond the processor directly to the enclosure with a thermal interface material.
Because larger components like CPUs, FPGAs, or GPUs have a BGA/LGA package, they can’t be used with thermal via arrays as they might not have a die-attached pad. However, an embedded copper column, called a copper coin, is one strategy that can be used to remove heat from a component. Copper coins have to be designed into the board as a press-fit element, and they will be subject to the same types of tolerances as one would see in press-fit holes.
Press-fit elements can be used as heat transfer elements when mounted below an integrated circuit.
A final type of structure that can be used for heat management is solder columns. A solder column is a large span of solder that is attached to a component package on the top layer. During assembly, these columns will form a very strong bond to an SMD footprint in the PCB. These structures are more common in component packages used in mil-aero systems that experience extreme levels of vibration, heat, and mechanical shock.
An example component package from Microsemi is shown in the image below. In this image, the solder columns are built into the package and will form a strong eutectic during assembly. They are often used with a carrier to provide a highly reliable assembly platform, but the additional solder used in these columns provides greater heat dissipation away from the package.
Example package with solder columns.
It’s Not All or Nothing
Effective thermal management in boards that produce a lot of heat involves a plurality of strategies. This can include a mix of press-fit/embedded copper, heavy copper, thermal interface materials, and fans or heatsinks. Some additional thermal strategies used in electronics assemblies include:
- Enclosure design to support forced and convective airflow
- Use of alternative substrate materials with higher thermal conductivity
- Placement of thermal interface materials for heatsinks
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