PCB Temperature Guide

Your Comprehensive PCB Temperature Guide

Materials and assembly aren’t the only factors involved in building a reliable printed circuit board (PCB). Temperature is a crucial factor in determining overall performance. Every degree shift affects material performance and lifespan.

Exceed a PCB’s heat tolerance, and layers can separate, components can fail, performance can degrade, and more, all impacting the design. This PCB temperature guide covers the basics of PCBs and temperature so you can plan the best PCB design for your needs.

Why PCB Temperature Matters for Board Reliability and Safety

Temperature decides how long a PCB can perform as designed. Every component reacts to heat in its own way, which can cause issues between individual components. When materials change by expanding or contracting, or hardening or softening, under different thermal loads, they can induce mechanical stress on themselves or other components. If temperatures rise too high or change too often, the damage accumulates. Eventually, you get warping, delamination, and electrical field drift.

How Heat Affects PCB Materials and Circuits

Every operating PCB generates heat. Electrical losses in components produce localized warming. Power devices and regulators run hottest, and copper planes spread that energy through conduction. When the temperature hits material thresholds, the board starts to change:

Dielectric layers: These soften as they approach their glass transition temperature (Tg). Repeated cycling around this point accelerates warping and impacts the dielectric constant.
Copper features: Like most materials, copper expands with heat, pulling against the dielectric layers around copper features. The stress leads to delamination, warping, and cracked vias. Rising temperatures also increase copper’s electrical resistance.
Solder joints and pads: These experience thermal fatigue due to repeated on-off cycles. Solder is sensitive to thermal cycling. The result is microcracks that turn into open circuits and intermittent connections.

All these issues compound, degrading electrical performance and signal integrity. Copper traces will not maintain consistent impedance, and the PCB’s structure will eventually weaken. Industry standards, such as IPC-6012 and IPC-TM-650, outline testing procedures for thermal stress, allowing teams to verify material performance.

During testing, look for physical warning signs like:

Solder mask discoloration
Layer delamination
Layer bubbling
Lifted pads or vias
Copper oxidation

Once these signs appear, the PCB’s structural integrity is already compromised. Testing and design should prevent these issues, so the PCB never reaches physical warning signs during its expected lifetime operation.

Local Hot Spots vs. Overall Board Temperature

PCBs heat unevenly. They all naturally experience stress and strain on a local level due to thermal expansion issues. These hot spots form around high-current components or power converters. Hot spots reach temperatures far above the board’s average. Engineers track three main temperature measures in PCBs:

Component junction is the temperature inside a semiconductor where power dissipates.
Local PCB hot spots refer to the surface or substrate temperature immediately beneath or around a component.
Average board temperature is the PCB’s overall heat level.

A stable average board temperature doesn’t mean you’re in the clear. Extremely warm hot spots will damage nearby parts, even if most of the board is at acceptable temperatures. Good thermal design distributes power devices, uses airflow paths, and often incorporates heat sinks and active cooling solutions like fans to efficiently dissipate heat from dense areas.

Matching Coefficients of Thermal Expansion

While all PCB materials expand when heated, they do so at different rates. Copper expands little, while resin systems expand further. The mismatch between their coefficients of thermal expansion (CTE) determines how much stress builds up between layers during heating and cooling. In a multilayer PCB, repeated thermal cycling can lead to layer warping or misaligned holes. Designers must choose materials with similar CTEs. This strategy lets the board expand uniformly and avoid stress.

PCB Temperature Limits and Essential Thermal Terms

Temperature limits define the extent to which a PCB can be pushed before its materials lose stability or electrical properties drift. When designing a PCB, these limits are a set of thermal thresholds. Boards can handle different kinds of stress at different levels over time. Each of these thresholds has its own term, which designers track to avoid performance problems:

Operating temperature: Every material has a continuous operating temperature, or the range where it can function indefinitely without measurable degradation due to thermal cycling. While brief excursions beyond this range are possible, they contribute to thermal fatigue, meaning the board can only withstand a finite number of these cycles before permanent damage or failure occurs, even if it returns to a stable state.
Tg: Tg marks the point where resin transitions from solid to softer and rubbery. When the board exceeds this limit, internal stresses increase, and the materials will deform under load.
Td: The decomposition temperature (Td) is the point where the laminate starts to break down chemically. Once it reaches Td, the PCB loses mass and can no longer maintain adhesion or dielectric strength.
RTI/MOT: The relative thermal index (RTI) indicates the highest temperature a material can withstand for 100,000 hours before losing key properties. The maximum operating temperature (MOT) applies to the entire PCB construction, not just one material. These measurements indicate to designers how long a PCB will last in years of service.

Typical Temperature Ranges for Common PCB Materials

Material determines how much heat a board can manage. The most common substrate, standard FR-4, typically offers Tg values between 266° F and 284° F (130° C and 140° C). This is an adequate range for consumer and low-power applications. For products that see higher operating temperatures, look for high-Tg FR-4 materials in the 338° F and 356° F range (170° C to 180° C). Designers will use polyimide, ceramic, or aluminum-based laminates for projects that need greater thermal endurance.

Common Causes of PCB Overheating

All PCBs generate heat while in operation, but certain factors can cause temperatures to exceed safe limits. Here are some of the most common times overheating happens:

High power density and component placement: Dense or compact layouts mean components share limited copper area. Sensitive components will drift or fail when placed near these hot spots. Poor layout and insufficient copper, used as a conductive heat sink, also reduce the board’s ability to spread heat evenly, creating temperature spikes.
High-frequency designs: Circuits running at higher frequencies experience greater dielectric and switching losses. They produce more localized heat even at moderate current levels.
High-speed designs: High-speed digital designs must manage trace geometry and dielectric loss without compromising impedance control.
Limited airflow: Enclosures can trap heat around the board, preventing natural convection. Horizontal board layouts might trap warm air pockets, while blocked vents further restrict airflow. A lack of active ventilation is also an issue.
Soldering and heat exposure: PCBs are exposed to extreme temperatures during the assembly process. Soldering temperatures for circuit boards that are too high or applied repeatedly can cause stress to components and lead to premature wear.

Overheating results from several of these factors combining to compound stress or from encountering one of them repeatedly. Working with your PCB supplier during the design phase helps address these issues before they affect the PCB assembly.

How to Measure PCB Temperature

Preventing overheating means knowing how to measure PCB temperature. A board that looks stable might fail due to hot spots once engineers apply power. Correct temperature measurement enables engineers to identify problems before operations incur expenses on full production.

Choosing a Measurement Method

Engineers can pick from several measurement options, based on their needs and budget:

Onboard temperature sensors: These methods measure local surface temperatures and can be designed directly into the circuit for continuous monitoring. They offer fast response, but only represent a small region where they’re placed. Options include SMT ICs and NTC thermistors.
Built-in junction sensors: Many microcontrollers and power devices include internal sensors that estimate junction temperature based on electrical parameters. They provide real-time monitoring but need to be calibrated against external readings. The reported temperature will lag slightly behind the actual die temperature without calibration.
Thermocouples or RTDs: These can be used for measuring PCB temperature in laboratory environments. Traditionally, thermocouples are onboard temperature sensors, but they can be applied externally for testing later. Sensors are taped onto specific board locations for accurate point measurements. However, they need careful attachment and insulation to avoid electrical interference.
Infrared thermography: This is a noncontact method that creates a thermal image of the board. The infrared technology shows hot spots or uneven heat distribution. Use infrared for design validation and failure analysis. Surface finishes can influence this method.

Best Practices for Sensor Placement

Good measurements also depend on sensor placement. The wrong placement will fail to capture accurate readings or hot spot locations. Identify the primary heat sources before placing. These areas will dissipate the most power and, therefore, create the most heat. Once you have the primary heat sources, you should:

Position sensors on a common copper or ground plane that connects to the heat source.
Keep sensors near the component body without affecting electrical spacing or trace routing.
Use thermal vias to improve heat conduction.
Mount sensors near the danger areas predicted by simulation and prototyping.
Place sensors directly under the hot spots on the opposite side for double-sided boards.

Avoiding Common Issues

Even experienced engineers can misread thermal data. It’s essential to control measurement setup and work with an experienced PCB partner. Here are the common heat measurement mistakes to watch out for:

Surface emissivity errors: Infrared cameras can misread temperatures if the PCB has different coatings or silkscreen colors. Use matte black tape or emissivity correction factors to keep data consistent.
Ambient and enclosure effects: Fan speed, airflow, and even nearby components can alter how heat accumulates. Always test on enclosed products, since open bench tests can underestimate the actual temperature reached during operation.
Poor documentation: Always record test data like results, ambient temperature, probe positions, and materials used. Otherwise, you can’t compare product data properly. Use clear labeling and consistent setups to create the most accurate evaluations between prototypes and revisions.
Local vs. average confusion: The PCB’s average temperature can hide dangerous hot spots. Teams should log data from multiple areas to avoid average measurement inaccuracies.

Managing Heat With PCB Design Techniques

PCB heat management is always evolving. Everything from design to testing influences how heat moves through the circuit and how the assembly performs. The goal is to control heat through careful modifications so the PCB runs reliably for years. Engineers will use various materials, configurations, and techniques to manage internal temperatures before resorting to external cooling solutions.

1. Copper Planes and Thermal Spreading

Copper planes are the primary solution for dissipating heat from components — continuous ground and power planes spread heat, dissipating localized energy across the wider PCB area. With proper plane use, designers can reduce temperature gradients and protect the PCB from warping or stress.

Thermal management needs to be large enough and properly connected to relevant regions to work. Any cutouts or signal routing can minimize their effect. Heat travels through the copper layers, creating an efficient flow of energy. Designers should reference IPC-2152 to build the most effective plane widths, copper weight, and current level designs.

2. Trace Width, Current, and Thermal Limits

The trace is the conductive path inside the PCB that carries electrical signals and power to components. As current travels along the trace, components can communicate with each other. But the greater the current, the greater the power loss. Narrow traces have a higher resistance and will heat more quickly under load. External traces cool faster than internal ones, since they radiate heat into the ambient air. Internal layers need greater width or copper weight to account for the slower cooling rate.

PCB designers also use IPC-2152 for calculating safe current-carrying capacity. It’s based on copper thickness and acceptable temperature rise. Engineers will design a copper trace that accommodates allowable temperature increases based on the specific application. The goal is to design a trace that carries the necessary power without overheating beyond allowable limits.

3. Thermal Vias and Pads

If a component generates constant heat, designers install thermal vias to let heat escape vertically. Via count and spacing will depend on the PCB’s copper thickness, board area, and power dissipation. Too few vias create heat bottlenecks, while too many reduce the board’s mechanical strength.

Vias are holes placed under exposed thermal pads. The thermal pad fills a gap between the heat-generating component, since air is a poor heat conductor. These pads are superior heat conductors — they efficiently capture heat and transfer it to the via and copper planes, spreading the energy throughout the entire structure.

4. Component Selection and Placement

Part choice is another influence on thermal control. Packages with exposed thermal pads or built-in heat-spreading layers perform better than those with dense layouts. If you have several power devices sharing a board, designers need to group them near copper-heavy areas or near airflow paths to maintain predictable heat distribution.

Any temperature-sensitive components, such as sensors, should be placed in cooler zones, away from converters or power amplifiers. Separation helps protect calibration accuracy, improve sensor precision, and support long-term stability. Collaborate with experienced designers to implement strategic spacing that reduces local temperatures.

5. Substrate Material and Airflow

A substrate’s thermal conductivity and expansion determine how fast hot spots spread and dissipate. Standard FR-4 materials conduct heat slowly. This can trap energy near high-power board regions. You’ll need to switch to laminates with a tighter temperature margin if you’re working with a narrow temperature range.

Airflow is also important. Fans, vents, openings, or strategic layouts in the PCB enclosure help move heat away from surfaces. Designers will also use vertical orientations to cool boards more effectively. This approach uses natural convection, where heated air, being less dense, naturally rises. It draws cooler air upward along the board’s surface and creates an efficient, passive cooling airflow.

All of these small details come together to create an effective, efficient PCB design.

6. Design Validation and Thermal Testing

After designing a high-temperature PCB, you need proof that it will perform as intended. Once they’ve completed a PCB layout, engineers will use thermal testing to verify real-world performance. Engineers will use power cycling and environmental chamber tests to simulate long-term operation. These tests show how quickly the board reaches equilibrium and whether temperature gradients form around high-current components.

Infrared thermography is one of the best tools for finding hot spots during early validation. Engineers will compare their hot spot maps against simulation data to confirm heat spread. They’ll also use accelerated life testing for boards exposed to continuous on-off cycles or continuous load. This testing identifies early material fatigue or solder joint cracking. With under-stress monitoring, engineers can see exactly how materials perform under long-term use.

It’s critical to integrate testing well before full-scale production. Receiving test results early enables designers and suppliers to adjust materials or layouts before the changes become too costly. Verifying actual heat behavior protects your full-scale production runs from major failures and ensures you deliver reliable PCBs.

When Do You Need a High-Temperature PCB?

Some PCB applications just run too hot for standard materials. High-temperature PCBs are commonly used in automotive engine sensors and lighting systems that are located near heat-producing components. Similarly, industrial motor drives and power converters are inside sealed enclosures or warm factory floors. If your application sees high ambient temperatures, constant high-power component exposure, or temperature swings, you likely need a high-temperature PCB.

Even products like LED lighting can exceed standard limits without seeming high-power. Installation in tight housings or outdoor spaces creates additional heat issues. Designs can face internal self-heating and external temperature changes with minimal airflow. Over time, users will see accelerated wear or failure. Consult your PCB design partner on materials rated for higher Tg and Td to improve stability.

Properties to Review When Selecting High-Temperature Materials

High-temperature-rated laminates aren’t one-size-fits-all. They have different temperature or moisture properties that influence their performance.

Tg and Td: Can the material handle lead-free soldering temperatures and long-term operating heat? Tg and Td influence their ability to avoid softening and degrading.
CTE: Check expansion rates in the x, y, and z axes. Larger CTE mismatches between copper and dielectric layers lead to cracking and delamination.
Moisture absorption: Outdoor or high-humidity spaces call for materials with low moisture absorption. Otherwise, you risk swelling, corrosion, and dielectric changes.
Time to delamination: This is how long the laminate resists layer separation at elevated temperatures. Longer times equal higher thermal endurance.

Why Trust Millennium Circuits Limited for High-Temperature PCBs

Millennium Circuits Limited (MCL) supplies PCBs for a wide range of applications. Every project has unique requirements, which is why we build PCBs to match engineers’ specific design needs. We focus on technical precision to ensure you get exactly what you need. MCL uses advanced fabrication technology and an extensive laminate selection to provide customers with dependable PCBs designed to perform in specific environments.

At MCL, we follow a rigorous quality management system certified to ISO 9001:2015. We are committed to maintaining consistent processes, ensuring traceability, and driving continuous improvement. We have extensive experience with high-Tg materials, heavy copper PCBs, and thermally strong builds. Combine our experience with detailed inspections and testing, and you can trust MCL to deliver the high-temperature resistance your project demands.

Plus, MCL’s engineering team will work closely with you to make the best decisions for your project. We can recommend laminate options, discuss material and assembly limits, and provide information on thermal performance to support your design goals. MCL is here to help you develop a PCB design that’s optimized for the most demanding thermal conditions.

Talk With MCL About Your High-Temperature PCB Projects

PCB temperature and thermal performance have a direct impact on product life and performance. The right materials and construction can prevent expensive mistakes and protect your application from operational issues.

If your next project involves high-temperature conditions, MCL can help. We’ll work with your team to select materials that align with your performance goals. We’ll walk you through material options and design considerations for stable, consistent high-temperature PCB assemblies.

Reach out to us to discuss your next PCB project.

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