What Happens When a PCB Gets Too Hot

Heat is one of the greatest enemies of electronic devices. When a printed circuit board (PCB) operates beyond its temperature threshold, a cascade of problems can occur, ranging from temporary performance issues to catastrophic failure. Understanding the causes and consequences of PCB overheating is essential for designing reliable electronic products with appropriate thermal management.

The PCB vs. Components: Different Heat Vulnerabilities

A point often overlooked is that modern PCBs themselves are extremely fire retardant. The FR in FR-4 (the most common PCB substrate material) literally stands for “flame retardant.” These materials are designed to withstand significant heat without combusting and will typically self-extinguish if exposed to flame.

The real vulnerability lies with the components mounted on the board. Semiconductors, capacitors, resistors, and connectors typically fail at much lower temperatures than the PCB substrate itself. While your FR-4 board might withstand temperatures up to 130°C without permanent damage, the components on it could begin failing at just 85°C or lower.

This distinction is important because it affects how we think about thermal management –  protecting sensitive components is usually the primary concern, even though we talk about “PCB overheating” as a general concept.

Temperature Thresholds: When Is “Too Hot” Actually Too Hot?

Let’s look at what actually happens when PCBs reach different temperature levels. These are potential thresholds where you’ll start seeing problems:

These ranges are general guidelines; specific components on the board may have more restrictive temperature limitations.

Immediate Consequences of PCB Overheating

1. Performance Degradation

When a PCB begins to overheat, the first observable effects are typically performance-related:

• Clock Speed Fluctuations: Processors and timing circuits may experience frequency drift
• Signal Integrity Issues: Increased noise and signal distortion
• Intermittent Failures: Components may temporarily malfunction and recover when cooled
• Reduced Battery Life: Power management circuits become less efficient
• Unexpected Resets: Protection circuits may trigger system shutdowns

These symptoms often appear before permanent damage occurs and should be treated as warning signs.

2. Physical Deformation

As temperatures continue to rise, physical changes to the PCB become apparent:

• Warping and Bending: The PCB substrate can deform, breaking solder joints
• Delamination: Separation between the copper layers and substrate material
• Solder Reflow: Solder joints may liquefy and create bridges or open circuits
• Component Shifting: Surface mount components may move from their intended positions
• Discolouration: The PCB changes colour, typically darkening or yellowing

These physical changes are often irreversible and compromise the PCB’s structural integrity.

Long-term Damage from Thermal Stress

1. Accelerated Component Aging

Even if temperatures don’t reach catastrophic levels, consistent operation at elevated temperatures dramatically reduces component lifespan:

• Electrolytic Capacitor Degradation: The electrolyte can dry out, reducing capacitance
• Semiconductor Degradation: Transistors and ICs experience accelerated aging
• Battery Damage: Lithium-ion batteries may swell or lose capacity
• LED Brightness Reduction: Light-emitting diodes lose luminosity over time

A rule of thumb in electronics is that component life decreases by approximately 50% for every 10°C rise above the rated temperature.

2. Material Breakdown

Extended exposure to high temperatures can cause chemical changes in PCB materials:

• Substrate Decomposition: The epoxy in FR-4 breaks down, becoming brittle
• Conductive Residue Formation: Flux residues can become conductive when heated
• Copper Oxidation: Increased oxidation rates at elevated temperatures
• Insulation Degradation: Insulating properties deteriorate, leading to potential shorts

These material changes compromise the electrical and mechanical properties of the PCB.

Catastrophic Failures

In extreme cases, excessive heat can lead to complete device failure:

• Component Rupture: Capacitors or other sealed components may burst
• Electrical Shorts: Melted solder or damaged insulation creates short circuits
• Trace Damage: Copper traces can detach from the substrate or melt

It’s worth noting that while components and solder connections fail regularly due to heat, the PCB substrate itself rarely catches fire. Modern PCB materials like FR-4 are engineered to be highly flame retardant – they’re designed to char rather than burn and will typically self-extinguish even if briefly exposed to flame. This is why you’ll often see damaged electronics where components have catastrophically failed while the PCB substrate remains largely intact, albeit discoloured and damaged.

That said, prolonged exposure to extreme temperatures far beyond design specifications can eventually overcome even these flame-retardant properties, particularly if other flammable materials nearby have already ignited.

Why PCBs Overheat: Root Causes You Can Fix

PCB overheating rarely happens by chance. Almost always, there’s a specific cause – or several working together – that pushes temperatures beyond safe limits. Identifying these issues early can save you from costly failures and production delays.

Design Missteps That Create Hotspots

Poor design choices are the most common culprits behind overheating boards. These fundamental errors can doom a PCB before it’s even manufactured:

• Inadequate Copper: When traces are too thin for the current they carry, they act like tiny resistors, generating heat. This is particularly problematic in power delivery paths where insufficient copper creates dangerous thermal runaway conditions.
  
• Poor Component Placement: Clustering heat-generating components (regulators, power transistors, processors) creates hotspots with nowhere to dissipate heat. The combined thermal output can quickly exceed what the board can handle.
  
• Missing Thermal Relief: High-power components need pathways to channel heat away. Without proper thermal vias or copper planes connected to these components, heat remains trapped and temperatures soar.
  
• Too-Thin Boards: Thinner PCBs might save space and material costs, but they sacrifice thermal mass. A thicker board absorbs and spreads heat more effectively, preventing localised hot spots from developing.
  

Environmental Triggers Beyond Your Control

Even well-designed boards can overheat when placed in challenging environments:

• Brutal Ambient Temperatures: Industrial equipment in factory settings or automotive electronics in engine compartments face ambient temperatures that start near component limits before the device even powers on.
  
• Suffocating Enclosures: Cramming PCBs into sealed, unventilated spaces prevents natural convection cooling. The trapped air heats up continuously until components fail.
  
• Solar Exposure: Direct sunlight can raise PCB temperatures far beyond ambient air, particularly when boards are housed in dark-colored enclosures that absorb rather than reflect heat.
  
• Thermal Neighbors: Mounting a PCB near other heat-generating equipment compounds the problem as each device heats the shared air, creating a progressively hotter operating environment.
  

Operational Stresses That Push Limits

How a device is used often determines whether it will overheat:

• Aggressive Overclocking: Pushing processors beyond rated speeds dramatically increases power consumption and heat generation, often exceeding thermal design parameters.
  
• Current Overloads: Running circuits at higher-than-designed current levels generates exponentially more heat—remember that power (and thus heat) increases with the square of current.
  
• Non-Stop Operation: Systems designed with the expectation of occasional downtime may overheat when run continuously, as components never get a chance to cool down to baseline temperatures.
  
• Power Supply Issues: Irregular voltage levels force components to work harder, generating more heat. Overvoltage conditions are particularly dangerous, as they increase power consumption across the entire board.
  

Keeping Your PCBs Cool: Practical Solutions That Work

Heat management isn’t an afterthought—it’s a fundamental aspect of PCB design that requires attention from the earliest planning stages. Here’s how savvy engineers prevent thermal issues from derailing their projects:

Smart Design Choices That Prevent Problems

The battle against excessive heat begins on the drawing board. Thoughtful design decisions pay dividends in thermal performance:

• Thermal Simulation: Modern CAD tools can predict hotspots before you build a single prototype. Spending time running thermal simulations identifies problems when they’re cheap to fix—during design, not after manufacturing.
  
• Strategic Component Placement: Distributing heat-generating components across the board prevents localised hotspots. Think of your board as a city map—you wouldn’t put all the factories in one neighborhood, and you shouldn’t cluster power-hungry components together either.
  
• Generous Copper Pours: Copper’s excellent thermal conductivity makes it your ally in heat distribution. Large copper areas act as heat spreaders, moving heat away from critical components. For high-current paths, be generous—a few extra millimeters of copper width costs almost nothing but provides significant thermal benefits.
  
• Thermal Via Networks: Vias (the small holes connecting layers) can create vertical heat pipes when properly arranged. A cluster of vias under hot components provides paths for heat to escape to other layers, particularly ground planes.
  
• Intelligent Layer Stacking: Internal ground planes aren’t just for electrical performance—they act as thermal radiators inside your board. A solid ground plane on layer 2 of a 4-layer board can dramatically improve heat spreading from surface-mounted components.
  

Component Choices That Run Cooler

The parts you select fundamentally determine your board’s thermal budget:

• Temperature-Tolerant Components: Components rated for automotive or industrial temperature ranges (-40°C to +125°C) provide thermal headroom that consumer-grade parts (0°C to +70°C) simply can’t match.
  
• Efficiency-Focused Alternatives: Modern low-power components often perform the same functions while generating a fraction of the heat. For example, switching regulators typically run much cooler than linear regulators for the same output power.
  
• Package Considerations: Larger packages with exposed thermal pads dissipate heat better than miniaturised alternatives. Sometimes, bigger really is better when thermal management matters more than board size.
  

Cooling Techniques That Make a Difference

When passive measures aren’t enough, active cooling solutions can handle even the most demanding thermal challenges:

• Heat Sink Selection: Not all heat sinks are created equal. Properly sized aluminum or copper heat sinks with appropriate fin designs can dramatically increase the surface area available for cooling hot components.
  
• Airflow Engineering: Fans need to be thoughtfully positioned to create effective cooling paths across hot components. The goal isn’t just moving air—it’s directing cool air precisely where it’s needed most.
  
• Quality Thermal Interfaces: The connection between components and heat sinks matters enormously. Premium thermal compounds, graphite pads, or phase-change materials can reduce thermal resistance by 30-50% compared to basic options.
  
• Alternative Substrate Materials: When FR-4 can’t handle the heat, aluminum core or copper core PCBs offer 8-10 times better thermal conductivity. These specialised materials cost more but enable designs that would be thermally impossible with standard materials.
  

How ABL Circuits Can Help

At ABL Circuits, we understand the critical importance of thermal management in PCB design. Our expertise includes:

• Thermal analysis of PCB designs to identify potential hot spots
• Guidance on material selection for high-temperature applications
• Design review services focused on thermal management
• Manufacturing techniques that optimise thermal performance
• Testing and validation under various thermal conditions

We work closely with our clients to ensure their PCBs meet both electrical and thermal requirements, resulting in reliable products with appropriate operating lifespans.

Whether you’re designing a high-power industrial controller, a compact IoT device, or anything in between, proper thermal management is essential for product reliability and longevity. Contact ABL Circuits today to discuss how we can help ensure your PCB designs stay cool under pressure.

Call ABL Circuits on 01462 514157 to learn more about our PCB design and PCB manufacturing services.