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How Packaging Styles Influence the Selection of Heat Sinks for SMD Components

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • Common SMD components used in PCBs are resistors, MOSFETs, linear regulators, ICs, etc.

  • The temperature of SMD components is influenced by the internal structure and the physical configuration of the package. 

  • For SMD components with packages such as SuperS08, through-hole heatsinks are soldered on another side of the PCB to implement a low-cost thermal management solution. 

PCB with SMD components

Designing and fixing heat sinks for SMD components can be a challenging task

The thermal management of through-hole components is comparatively easier than surface mount components. Designing and fixing heat sinks for SMD components is a challenging task. In this article, we will explore the thermal management of SMD components, including the influence of SMD packages and power losses on thermal management and heat sink design for SMD components.  

The Thermal Management of SMD Components

Surface mount technology enables the manufacturing of compact, miniaturized, and high-power density PCBs. SMD components can be populated on both sides of the PCB, helping to develop a dense package. SMD components permit the fabrication of efficient and versatile circuit boards of smaller sizes. These components incorporate not only logic circuits but also power and switching devices.

The common SMD components used in PCBs are resistors, MOSFETs, linear regulators, and ICs. SMD components generate heat, and the temperature rise can cross the safe operating limits of the components. Self-heating can shorten the lifespan of SMD components or can lead to complete damage. It is important to remove the heat from SMD components to ensure the risk-free operation and proper functioning of adjacent components.

Size reduction, high-density board assembly, increased ambient temperature, and increased power losses deteriorate the thermal performance of SMD components and require improved thermal management techniques. 

The Influence of SMD Packages and Power Losses on Thermal Management 

SMD components are available in different packages, such as D PAK, D2PAK, D3PAK, etc. Each of these packages has a different thermal path. For the same power levels, the temperature measured in each package varies. It can be summarized that the temperature of SMD components is influenced by their internal structure and the physical configuration of the package. It is important to select the thermal management technique that is compatible with the packaging style of the SMD component.

Power loss in SMD components is an important criterion for the selection of thermal management techniques. Thermal management can be achieved in several ways, including:

  1. Heat dissipation through the contact pads on the PCB
  2. Heat sinks

Contact pads are a suitable thermal management method for power levels below 2W; this is accomplished by placing thermal pads under any hot parts and removing the heat from the pads to the ground planes through vias. 

Heat Sinks for SMD Components: DPAK, D2PAK, and D3PAK Packages

Heat dissipation in SMD components differs depending on the package. Packages such as SOP Advance dissipate heat only from the bottom surface, whereas the DSOP Advance package dissipates heat from both the top and bottom surfaces. When it is difficult to remove heat using copper inlays or thermal vias, heat sinks are the best solution. Attaching heat sinks to SMD components brings heat removal capabilities that are equivalent to the traditional contact pad technique.

For SMD packages D PAK, D2PAK, and D3PAK, punched SMD heat sinks are preferred. These heat sinks are extremely flat and are well-suited for these packages. To attach an SMD heat sink, the copper drain pad of the SMD component is extended beyond the edges of the package. The extension provides space to mount the heat sink on top of the SMD component. Punched SMD heat sinks and the SMD component are soldered to the copper drain pad, creating a thermal path between the package and the SMD heat sink. The protruding fins or the wings of the heat sink increase the surface area as well as the airflow available for heat dissipation and enhance the efficiency of this thermal management technique.

The heat transfer mechanism of thermal conduction and natural convection aids the heat removal from SMD components using heat sinks. These types of heat sinks are not in direct contact with the device's surface. Thermal interface materials (TIMs), often thermal grease, are used for interfacing the top of the SMD component with the heat sink. The TIM fills the uneven surfaces between the SMD component and heat sink, thus eliminating any gaps between them. The TIM plays a significant role in increasing the thermal conductivity of heat sinks for SMD components.

Low-Cost Heat Sinks for SMD Components in Single-Sided PCBs

It is difficult to add thermal vias in single-sided PCBs; in certain single-sided PCBs, heat sinks on top of the SMD components are impractical due to various mechanical constraints. For SMD components with packages such as SuperS08, through-hole heat sinks are soldered on another side of the PCB to implement a low-cost thermal management solution. A thermal connection is established between the heat sink and SMD components through PCB copper tracks. In this type of heat sinking for SMD components, the device is always placed near the solder connections of the heat sink.

Thermal vias and heat sinks for SMD components can be combined to enhance the thermal performance of an electronic design. You can rely on Cadence’s suite of design and analysis tools to aid in the design of thermal management solutions for SMD components. Cadence software offers simulation tools that can analyze the temperature profile of SMD components under different heat sink connections.

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