Practical guidelines on PCB thermal relief for efficient PCB manufacturing!

By Mer-Mar Electronics Date posted: Last updated: May 19, 2022
PCB Thermal Relief Guidelines

When it comes to the efficiency of a circuit board, managing and conducting heat efficiently is extremely important. Whether your PCB is a single layer, simple PCB or a complex multi-layer printed circuit board, it is likely to have large areas of metal on it. This large metal area, whether it is a network of wide traces or a large, filled power plane, can, in turn, cause issues with soldering. Some of these include:

  • Through-hole component pins: If these pins do not get enough heat for soldering, you can land up with a cold solder joint. What could also happen is that if you try to unsolder a through-hole, you could land up applying too much heat on it. In turn, this heat can damage components and/or traces.

  • Surface mount component pins: In two-pinned SMT parts there could be an issue if there is unbalanced metal between the pins. In such case the solder could melt faster on one side than the other. This could move the part away from the other pin.

With design engineers wanting to use a lot of metal for electrical purposes, what you typically see is a conflict between the board’s electrical needs and its manufacturing requirements. Thermal relief is therefore the need of the hour.

For through-hole component pins, thermal relief can be offered by way of a connecting pad with small voids in it. These voids create metal spokes that, in turn, restrict the heat that is conducted from the barrel of the hole during soldering to the rest of the metal trace. In case of a surface mount part also spokes are used to connect the solder pad to the metal trace.

Here are some practical guidelines for PCB thermal relief, which if followed effectively, will lead to efficiency of the custom printed circuit board:

PCB Thermal Relief Guidelines:

  • A thermal relief pad is used wherever a through-hole pin is connected to a metal or power plane.
  • Where SMT parts are soldered to large metal areas, there needs to be thermal relief between their solder pad and the metal.
  • The amount of power conducted by the pin determines the number as well as the width of spokes in a thermal relief pad. For example, if the power needs a minimum trace width of 30 mils, you need to ensure that the thermal relief pad should have 30 mils of spokes attached to it.
  • Vias typically do not need a thermal relief pad as they do not have a pin soldered to them. However, in case of nets with high current levels, there could be power traces that conduct too much heat to the surface mount pins. In such cases a thermal relief pin is needed.
  • It is imperative that the rules of setting up thermal relief pads in CAD systems are fully understood. Basis the rules, you will need to work out the following:

    • Size of spokes
    • Its shape
    • Number of spokes
    • Width of spokes
    • Minimum spokes possible
  • It is also important to adhere to rules to do with minimum thermal relief connections. There can be issues if the thermal relief pads are too close or if they are being used in a split plane.
  • Ensure that you know the terminologies associated with components and pads such as:

    • Termination and termination width
    • Tolerance
    • Overlap

A thorough knowledge of the underlying rules before you start the layout can go a long way in ensuring success. In fact an experienced electronic contract manufacturer can go a long way in helping you with these issues. Not only will the contract manufacturer know what is needed with thermal relief to create good solder joints, they are also aware of any issues that you may face based on the material used, the layers as well as the manufacturing processes.

To sum up

Thermal relief makes a huge difference in the functionality and performance of the circuit board. Reliable PCB manufacturers have the skills and the expertise to determine what kind of thermal relief your design needs. They can therefore suggest the alternatives depending on viability as well as cost-effectiveness of the various alternatives.

As a leading electronic contract manufacturer in USA, we provide one stop solution for electronic contract manufacturing services with specialized support, reliable testing, and multi-functional features. To know more contact us at sales@mermarinc.com or call us on (760) 244-6149.

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