What Is Thermal Relief in PCB Manufacturing?
Have you ever heard of thermal relief in PCB manufacturing? If not, you’re not alone. It’s a technical term that’s not often discussed outside of the industry. However, if you’re involved in designing or manufacturing printed circuit boards (PCBs), it’s critical to understand what thermal relief is and why it’s so important.
In this article, we will explore what thermal relief is, how it works, and its importance in the PCB manufacturing. Whether you’re a designer, engineer, or manufacturer, understanding thermal relief is crucial to ensure the quality and reliability of your PCBs.
What Is Thermal Relief in PCB Design?
A thermal relief pad is one part of proper heat management for PCB design. It helps keep heat from dissipating to nearby areas, keeping the heat concentrated around the pin being soldered.
Thermal reliefs are small copper pads placed next to the connections for the pins of electrical components on a circuit board. The relief is often made from a group of copper spokes surrounding the pin or via.
Thermal reliefs are often used around thru-hole pins and surface-mount pins where a stronger solder joint is needed. Heat relief pads are also used when the pins connect to a large copper plane on a multi-layer PCB.
Using thermal relief in PCB designs can help with the manufacturing process and quality of the PCB. Thermal reliefs create a stronger bond by ensuring that heat from the soldering iron remains concentrated on the solder joint.
This is more important when using automated soldering processes, as a direct connection between the pin and the pad creates a heat sink. The heat sink can absorb heat during the soldering process, resulting in a weaker joint.
The thermal relief helps separate the pin or via from the copper plane, making the area easier to solder. You can spend less time heating the pin, which decreases the risk of overheating the surrounding components.
When a pin connects to a large metal plane, heat from the soldering tool can transfer to other components. The excess heat may eventually damage other areas of the board. Adding a thermal relief pad is a simple solution for keeping the heat in place when soldering.
Thermal Relief PCB Footprint
The PCB footprint refers to the copper areas that electronic components connect to. A thermal relief has its own PCB footprint. When used around a surface-mount pin, thru-hole pin, or via, a thermal relief pad is often a broken circle featuring a series of spokes.
The design may include three or more spokes, depending on the power being conducted through the pin. However, not all thermal relief pads include a circular design.
For example, the footprint of a thermal relief pad for a square-shaped SMT device is likely to include straight lines that separate the SMT pad from large copper planes on the surface of the PCB.
Guidelines Related to PCB Thermal Relief
Standard PCB design guidelines suggest using PCB thermal relief in specific areas when there is a risk of overheating or heating nearby components. Here is a closer look at some of the areas where you are most likely to use thermal reliefs.
Thermal relief can help when soldering surface mount pins from small components. Using a metal fill pad takes heat away from the pin, which increases surface tension and can pull the pin away from the PCB. A thermal relief pad is also recommended when soldering surface-mount technology (SMT) devices to large planes of metal.
Thermal reliefs are often used on through-hole pins, especially in large PCBs with multiple layers. A thermal relief pad is typically added to a thru-hole pin when the pin connects to a power plane.
The metal that connects with the thru-hole pin takes heat away during the soldering process, resulting in a weaker bond. Adding thermal relief to a thru-hole pin ensures a better connection. It helps heat stay in place instead of dissipating to nearby pins.
Read Also: Guide to Understanding Through Hole PCB
Vias do not typically require thermal relief or heat relief, as they do not typically connect to as many layers as a thru-hole pin.
However, some vias may conduct more electricity than others, which can draw more heat to the pins. Using a thermal relief on a via with a high current can result in a better solder joint.
Not all metal routing requires thermal relief. Power traces that conduct less electricity are often designed with a narrow profile. The narrow traces can eliminate the need for thermal relief.
How Do You Calculate the Thermal Relief of a PCB?
The width and number of spokes in a thermal relief pad depend on the width of the traces. The size of the thermal relief is correlated to the amount of power that the pin conducts.
If the PCB trace requires a width of 50 mils, the thermal relief pad should offer 50 mils of copper thermal relief. This would require five spokes measuring 10 mils wide or four spokes measuring 12.5 mils wide.
The distance between the thermal relief pad and the copper pad must also be considered. In most cases, the thermal relief pad should sit 0.005 inches (5 mils) away from the copper pour.
Determining the size of the thermal relief for an SMT pad is a little different. Multiply the length of the SMT pad by 0.60. Divide the result by the number of thermal relief traces or pads.
For example, suppose you have an SMT pad measuring 100 mils long and two thermal relief traces. Each thermal relief pad would need to measure 30 mils wide (100 times 0.60 = 60 / 2 = 30).
You can also find calculators for estimating the size of thermal relief traces based on the power conductivity of pins and the size of the SMT pads. Many PCB design applications also include features for adding thermal relief pads and automatically calculating the width.
Knowing when to use thermal relief in PCB design can help increase the quality of a circuit board. A thermal relief pad helps separate pins, vias, and SMT pads from nearby copper planes, which prevents heat from dissipating. Concentrating the heat on the pins or pads ensures a stronger solder joint and protects nearby components during the soldering process.
A thermal relief pad is a necessary part of proper heat management. Make sure that you consider using thermal relief pads when needed to improve the performance of your board design.
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