Best Practices for Heat Dissipation in PCB Design: A South African Guide

Overview: Why Heat Dissipation Matters in PCB Design

As electronic devices grow smaller and more powerful, effectively managing heat on printed circuit boards (PCBs) has become crucial for reliability and safety. Excessive temperatures can cause component failure, thermal drift, and reduced product lifespan-particularly relevant in South Africa's summer months and enclosed environments.

PCB Thermal Management Basics

Heat generated by ICs, voltage regulators, power transistors, and other components must be conducted away from sensitive circuits. Key goals include lowering thermal resistance, spreading heat, and preventing hotspots.

• Direct heat safely from active devices to board edges or external heatsinks.
• Avoid placing heat-sensitive ICs next to high-power dissipators.
• Use wide copper traces and thermal vias to facilitate heat flow.

Industry Standards and Key Thermal Specifications

PCB manufacturers and designers refer to thermal parameters to quantify heat management capability. Important factors include:

Datasheets for semiconductors, MOSFETs, and regulators often list safe maximum junction temperatures and recommend board layouts to improve heat dissipation. Always review these details when selecting locally stocked parts from Communica.

Optimising PCB Layout for Thermal Performance

The following PCB layout practices can substantially reduce temperature rise:

• Place hot components away from each other and allow space for airflow, especially near board edges.
• Use wider copper traces and planes for power delivery to double as heat conductors.
• Implement thermal relief pads for through-hole components and expose copper under power ICs.
• Add thermal vias below heat-generating ICs to connect top and bottom layers.
• Consider multi-layer boards or add dedicated internal planes for high-power builds.

Example of Simple Thermal Pad & Via Layout:

IC


       Thermal      
       Pad Area     
 
       (Thermal vias below IC)

This method helps transfer heat from the IC down to larger copper areas or to the opposite side of the PCB for better cooling.

Component Selection and Accessory Integration

Selecting the right parts is just as important as the board layout. Prioritise semiconductors rated for higher ambient temperatures (often 85 degreesC+ for industrial parts), and consider:

• Heatsinks: Clip-on or screw-mount types are available locally for TO-220, TO-247, and SOIC packages.
• Thermal pads, pastes, and adhesives: Improve the interface between components and heatsinks, available from known brands at Communica.
• Active cooling: For high-power boards, small fans can help in compact enclosures.

Explore the Thermal & Heatsinks and Power categories for local availability.

Calculating Temperature Rise: A Practical Example

Let's work through a common calculation for a South African lab power supply using a linear voltage regulator (7805):

• Assume: Vin = 12V, Vout = 5V, Load = 0.5A
• Power Dissipated = (Vin - Vout) x Iout = (12V - 5V) x 0.5A = 3.5W
• If JA for 7805 (without heatsink) is 65 degreesC/W:
  Temperature Rise = 3.5W x 65 degreesC/W = 227.5 degreesC
  (Clearly, a heatsink is needed!)

With a modest heatsink (JA drops to 25 degreesC/W):
3.5W x 25 degreesC/W = 87.5 degreesC above ambient. For a local room at 25 degreesC, junction temp is 112.5 degreesC; keep below the device's max rating (~125 degreesC-150 degreesC).

Troubleshooting Overheating in Prototypes

• Use a thermal camera or IR thermometer to locate hotspots.
• Check for airflow obstructions in enclosures or project boxes.
• Test with elevated input voltages-South African mains float between 220-240V AC, affecting regulator drop and heat output.
• Rework thermal vias or add copper pours if hot spots persist.

Summary Checklist: Best Practices for PCB Heat Dissipation

• Start with thoughtful component placement for airflow and separation.
• Maximise copper area with wide traces and pours, especially under power devices.
• Add ample thermal vias for multi-layer boards in power sections.
• Choose compatible heatsinks and use thermal interface materials correctly.
• Confirm with real-world tests using tools like DMMs and thermal cameras.

Sources

• Texas Instruments: PCB Thermal Management Guidelines
• Analog Devices: Practical PCB Thermal Design
• Communica: Thermal & Heatsinks Collection
• Altium: PCB Thermal Vias and Heat Dissipation
• Communica: About Us