Understanding Thermal Dissipation Versus Thermal Distribution for Circuit Boards

December 10, 2019 , in Blog

I wonder if the person who discovered fire had any idea of the significance of this achievement. It is doubtful that anyone truly realized how impactful the ability to change the temperature of the immediate environment as well as materials would be. However, it is likely that the most basic usage of heat to stay warm in cold weather was quickly understood. As great as having fire was, it eventually became apparent that we also needed to be able to control it. This meant that sometimes we needed to dissipate it and sometimes distribute it, which has led us to the heating, ventilation, and air conditioning (HVAC) units that are commonplace today.

HVAC units

Thermal dissipation and distribution units

Controlling heat or thermal dissipation and distribution are very important for building and using circuit boards and failing to manage heat transfer can also ruin your board. This includes being able to dissipate excess heat; for example, using a heat sink, and distributing without overloading traces and vias. Therefore, it is incumbent upon designers to have a good understanding of thermal properties and how to apply good thermal design for manufacturing and operation principles. Let’s see why thermal design is important by first reviewing heat transfer methods and then comparing thermal dissipation and thermal distribution.

Circuit Board Heat Transfer

Electric circuits are designed to move current between and through components. During this process, heat is generated. This heat may be transferred from the source in one of three ways:

  1. Radiation: This is the transfer of heat from or into a material from its surroundings; such as the air. Transfer out is emission and into is absorption.
  2. Conduction: Here, two surfaces of different temperatures are in physical contact and heat moves from one to the other.
  3. Convection: This is the process used to forcibly distribute heat and air conditioning throughout structures; such as vehicles and buildings.

Naturally, heat always moves from the higher temperature area or material to the lower in search of equilibrium or a constant temperature throughout and managing the heat transfers on your board is a design requirement. That means managing or controlling the conduction and convection of heat on your board for manufacturing and operation. Doing so requires that you institute methods to control thermal dissipation and thermal distribution.

Thermal Dissipation versus Thermal Distribution

Both thermal dissipation and distribution management are concerned with the adequate movement of heat. However, dissipation is the process of removing excess heat from the board entirely, while distribution is the process of ensuring that excess heat is not concentrated, but evenly distributed. The table below compares and contrasts this and other attributes of these two thermal properties.

THERMAL DISSIPATION

versus

THERMAL DISTRIBUTION

Removal of excess heat

Heat transfer objective Even distribution of heat
Operation Important stage

PCB assembly (PCBA)

Controlling thermal resistance

Management

Controlling thermal resistance

As shown above, thermal dissipation is an issue for operation in the field, while distribution is a concern for board assembly. However, both are managed by controlling thermal resistance. Thermal resistance can be defined as the property of a material to resist the flow of heat. For dissipation, the materials of primary concern are the traces; including surface routes and thermal vias, which are plated through-holes (PTHs) specifically placed to pass heat, not current. For distribution, the stackup materials, especially substrate dielectric constants, are of primary interest as they define the board’s resistance. Additionally, for SMTs thermal reliefs can be used instead of full component pads which are easier for assembly rework.

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When designing PCBAs, it is important to know the difference between thermal dissipation and thermal distribution and what design choices impact each. However, both are important as your distribution design choices can affect your board’s manufacture and dissipation decisions can impact your board’s operation. At Tempo Automation, the industry leader in manufacturing high-quality PCBAs, fast, we will work with you to ensure that both of these design concerns are addressed.

And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on thermal dissipation and/or thermal distribution, contact us.

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