PCB Thermal Design Basics (2): Component Layout

Introduction: The Decisive Role of Component Layout in PCB Thermal Design

In modern electronic systems, the reliability and performance of a PCB directly depend on its thermal management capabilities. As power density increases and product size shrinks, component placement has become critical to ensuring long-term stable operation. The quality of the layout not only dictates how efficiently heat can be dissipated but also directly impacts the board's electrical performance and component lifespan.

Improper component placement is one of the primary causes of localized hotspots and areas suffering from high thermal stress. These hotspots can lead to increased copper trace resistance, voltage drops, efficiency reduction, and even cascading component failures. Therefore, design teams must initiate rigorous thermal design during the pre-development phase. By optimizing component arrangement, spacing, and thermal pathways, designers can avoid costly prototype rework, ultimately enhancing product reliability, manufacturability, and cost-effectiveness. The core objective of component placement, therefore, is to achieve optimal heat dissipation through physical design by optimizing the heat transfer path and maximizing the heat spreading area.

1. > Recommend reading: 
2. PCB Thermal Design Basics (1): Substrate Material Selection
3. PCB Thermal Design Basics (3): PCB Wiring Layout

Table of Contents

PCB thermal management should be addressed at the project architecture stage, rather than being treated as a verification step at the end of the design process. Component placement is the crucial physical implementation that determines a PCB's ability to operate reliably within specified temperature limits, with the core goal of minimizing thermal resistance and maximizing heat spreading capability.

1.1 The Core Role of Thermal Simulation in Modern PCB Design

Effective thermal management begins with predictive modeling. Designers utilize Electronic Design Automation (EDA) tools or Computational Fluid Dynamics (CFD) tools for thermal simulation to identify potential hotspots and high-temperature affected areas before physical layout is finalized.

1.1.1 Pre-Layout Modeling: Guiding Architecture Optimization

Firstly, software thermal analysis must be conducted to control the internal maximum temperature rise, aiming for the shortest possible heat transfer path and the largest possible heat transfer cross-section. Pre-layout simulation allows engineers to pre-determine the optimal component locations, copper structures, stack-up arrangements, and heat sink performance requirements. Through this early analysis, design teams can efficiently optimize heat distribution and spreading across the board, thus avoiding costly and time-consuming prototype corrections.

Layout constraints must be strictly architectural. If the actual layout deviates significantly from the simulation model, the thermal performance guarantee will be void. Therefore, the initial placement of high-power devices should be treated as an immutable architectural requirement. By deeply understanding the thermal behavior early in the design phase, engineers can gain confidence to reduce PCB size or simplify the cooling solution, while maintaining acceptable temperature limits.

1.1.2 Defining Boundary Conditions and Heat Transfer Mechanisms

Accurate thermal simulation requires setting realistic boundary conditions (BCs), which must cover all three primary heat transfer modes: conduction through solid materials, convection via fluid (e.g., air) motion, and radiation via infrared energy.

Key boundary conditions inputs include ambient temperature, airflow characteristics, surrounding objects, PCB mounting surfaces, and Thermal Interface Material (TIM) parameters. For natural convection (still air) scenarios, the Heat Transfer Coefficient (HTC) can be taken as 5–15 W/m²·K as an initial estimation, and sensitivity analysis should be performed considering geometry and ΔT; simulation and experimental calibration are prioritized. PCB and IC surfaces' radiation emissivity is typically 0.8–0.95 depending on the coating; environmental radiation temperature relates to the packaging/enclosure temperature field, requiring view factors/cavity models when necessary.

> Recommend reading: PCB Surface Finishing 101: Processes, Pros & Cons

1.1.3 Fundamental Principles of Heat Transfer and Thermo-Electric Feedback

The core of PCB thermal design lies in following the fundamental principles of heat transfer: the path must be the shortest, and the cross-section must be the largest. Maximizing the copper area dedicated to the heat conduction path is the primary strategy for reducing component junction-to-ambient thermal resistance.

Localized hotspots increase the electrical resistance of copper traces, leading to voltage drops and efficiency reduction. Therefore, using wider/thicker copper traces to lower electrical resistance directly reduces heat generation, achieving a fundamental improvement in thermal performance.

II. Overall System Layout and Airflow Management

At the system level, component placement involves positioning relative to the enclosure, other boards, and the system's cooling environment, requiring strict adherence to system-level, airflow management, and integration requirements.

2.1 PCB Orientation and Convection Strategy

The choice between natural or forced convection dictates the optimal component arrangement.

2.1.1 Optimizing Natural Convection: Vertical Mounting and Staggering

To maximize heat dissipation efficiency, it is recommended to mount the printed board vertically; the distance between boards should generally be no less than 2 cm. Vertical mounting fully utilizes the natural chimney effect of hot air rising. For natural air cooling, components should be arranged longitudinally (along the length) to maximize the vertical airflow channel. As shown in Figure 2.1.1 “Natural Convection,” this longitudinal arrangement fully utilizes the natural chimney effect.

Figure 2.1.1  Natural Convection

To reduce the “pre-heating effect”, high-power components should be prioritized at the bottom (to meet cooler air) in the vertical direction, and moderately staggered on the plane to expand fresh air coverage.

2.1.2 Forced Convection System: Component Arrangement and Airflow Path Design

When forced air cooling (fans) is used, components should be arranged laterally (perpendicular to the airflow direction) (as shown in Figure 2.1.2 “Forced Convection”) to expose the maximum surface area to the cooling air.

Figure 2.1.2  Forced Convection

Thermally Sensitive Component Placement: Thermally sensitive components (such as sensors, precision analog ICs) should typically be placed near the air inlet to utilize the coolest air.

High-Power Component Placement: High heat source positioning must be balanced via CFD/testing, not rigidly placed downstream. The position of high-heat generating components should be optimized based on the objective function (lowest junction temperature vs. protecting sensitive components) to prevent premature air pre-heating and subsequent reduction in overall cooling effectiveness.

Heat sink fins must be aligned with the airflow direction inside the enclosure to maximize heat dissipation efficiency. Poor alignment of heat sink fins may cause cooling efficiency to significantly decrease (two-digit percentage magnitude), specifically depending on the flow velocity and fin geometry.

Forced Fan Power Determination: The power of forced cooling should be determined through fluid dynamics calculations based on the mounting space, fan blade size, and the acceptable temperature rise of components during normal operation. Selection must be based on the required volumetric flow rate and system impedance curve (P–Q matching), diameter (2–6 in) is only one of many factors.

2.1.3 Avoiding Airflow Short Circuits and Ensuring Duct Consistency

Vents for heat dissipation should be reserved on the board, and overly tall components should be avoided near the air inlet to prevent obstructing cooling. Designers must study the air flow path. Since air always tends to flow toward the path of least resistance, large void areas should be avoided when placing components on the printed circuit board to prevent air from bypassing hot components and causing an “airflow short circuit.” If large void areas exist, baffles/multi-point inlet designs should be incorporated to prevent bypass.

Furthermore, forced ventilation direction must be consistent with the natural convection trend, and supplementary boards/components' air ducts must align with the ventilation direction, maintaining adequate distance between the inlet and exhaust.

2.2 System Integration: Utilizing Chassis and Enclosure for Heat Dissipation

Components with high heat generation and radiation may be designed and mounted on a dedicated printed board. Heat-generating components should be placed as high as possible in the product, and ideally within the airflow channel if conditions allow.

Transferring heat to the external chassis is one of the most critical system-level conduction paths. Utilize the metal chassis or baseplate for heat dissipation whenever possible. High-power components should be mounted using screws or other mechanical interfaces whenever possible to ensure highly efficient heat conduction to the chassis or baseplate. This often requires placing these parts near the board edges or mounting holes.

For extremely high-power density applications, such as power modules or base stations, Metal Core PCBs (MCPCBs) offer a robust solution. MCPCBs (especially Aluminum core PCBs) exhibit thermal conductivity far superior to traditional FR4 materials' thermal conductivity.  (See The FR4 Thermal Conductivity Overview) The metal core acts as an integrated heat sink, quickly transferring heat away from critical components.

> Recommend reading: Copper-Core PCBs

III. Local Detail Placement: Hotspot Control and Component Spacing

Within the circuit board, we focus on the precise positioning of components to manage localized heat conduction and thermal radiation effects.

3.1 Power Component Distribution Strategy

Component placement requires a trade-off between “uniform heat spreading” and “concentrated heat dissipation.”

3.1.1 Uniform Heat Distribution vs. Concentrated Cooling

Uniform Spreading: The board surface thermal capacity should be distributed uniformly. Designers should spread high-power components evenly across the board to avoid localized hotspots. Avoid concentrating high-power components.

Concentrated Cooling: If concentrated placement of high-power components is unavoidable, shorter components should be placed upstream of the airflow, ensuring sufficient cooling airflow passes through the concentrated heat zone.

Edges and Corners: Components with high heat or high current should not be placed in the corners and edges of the printed board, unless active cooling is provided nearby. Horizontally, high-power components should be positioned near the board edge to shorten the heat transfer path. Vertically, high-power components should be placed closer to the top of the printed board to reduce their temperature impact on other components.

3.1.2 Managing Thermal Interference and Isolating Sensitive Components

Component placement must account for the thermal radiation effects on surrounding parts. Thermally sensitive components must be strictly isolated from high heat sources.

Sensitive Component Placement: Thermally sensitive components (including semiconductor devices) should be distanced from heat sources or shielded, ideally placed in the coolest area of the system (such as the bottom of the enclosure), examples include pre-amplifiers requiring low thermal drift.

Electrolytic Capacitor Lifespan: Liquid dielectric capacitors (such as electrolytic capacitors) are extremely sensitive to temperature. They should be kept away from heat sources, and must never be placed directly above heat-generating components. The expected lifespan of a capacitor is approximately halved for every 10°C rise in temperature.

Layout Order's Impact on Temperature Rise: As shown in Figure 2.1.1, the arrangement of integrated circuits directly impacts temperature rise. LSI's power consumption is 1.5 W, and SSI's is 0.3 W. Experimental results showed that the optimized layout (b) led to a significantly lower temperature rise compared to the sub-optimal layout (a). Adopting the optimized layout is more favorable for reducing the failure rate of the LSI.

3.1.3 Quantified Separation Distance Standards

Control thresholds are derived backward from the junction temperature margin and lifespan model (e.g., Capacitor Arrhenius, Semiconductor FIT). For high-heat sources (defined by lifespan/junction temperature requirements), the following isolation guidelines apply.

Isolation Distance Principle: The isolation distance should be derived backward from the capacitor case temperature limits and verified through CFD/measurement.

Common Reference Range: (Empirical starting point) A sample or CFD scan can be performed within the 10–30 mm range, selecting the distance based on case temperature limits and lifespan models.

3.2 Copper Feature Design for Local Heat Spreading

3.2.1 Wide Traces for High-Current Paths

High-current paths must use sufficient trace width and thickness to provide a low impedance path. Wider traces reduce electrical resistance, minimizing I²R loss and the accompanying heat generation.

3.2.2 Maintaining Uniform Copper Area Distribution

To enhance the board's heat dissipation and reduce warping caused by uneven copper distribution, the conductor area laid on any single layer should comply with the PCB manufacturer's copper balancing specification (commonly 30–70% range or localized difference constraints). Use copper thieving/mesh copper when necessary; avoid blindly pursuing a fixed percentage.

IV. Enhanced Board Conduction: Thermal Vias and Material Upgrades

The most effective method for highly efficient vertical heat transfer is the use of thermal vias and optimized substrate materials. This is key to minimizing internal thermal resistance.

4.1 Thermal Via Array Design and Implementation

Thermal vias are plated through-holes that provide a low-resistance vertical thermal path between layers.

4.1.1 Via-in-Pad Technology for BGA and QFN Devices

For high-power IC packages, thermal vias must be placed directly beneath or within the component's exposed thermal pad (via-in-pad), ensuring the shortest, lowest-impedance thermal path from the die junction to the internal copper planes.

4.1.2 Thermal Via Design Parameters and High Copper Connection

To achieve efficient heat transfer, the thermal via diameter is typically between 0.2 mm and 0.4 mm (8–16 mil). The spacing between vias should be determined based on the pad size and manufacturing capability. The key to preventing solder wicking is the use of copper/resin fill and capping (IPC-4761 Type VII, etc.). Thermal vias must connect to large copper areas, such as internal power or ground planes, to effectively spread the heat.

Using heavy copper (e.g., 3 oz or thicker) for internal planes can significantly reduce in-plane thermal resistance, but simultaneously increases thermal capacity and mass, and impacts signal integrity (SI)/minimum line width/spacing due to process limitations, requiring joint SI/DFM evaluation.

4.2 Optimizing PCB Stack-up Design

Utilizing a multi-layer board structure aids PCB thermal design. Power and ground planes should be strategically placed close to the component layer. Copper's thermal conductivity (approx. 400 W/m·K) makes it an excellent material for heat spreading. For power-intensive PCBs, 2 oz or even 3 oz copper is recommended for power and ground planes.

4.3 Substrate and Laminate Selection

4.3.1 Requirements for High-Performance Laminates (T_g and K)

Select flame-retardant or heat-resistant board materials. Lead-free processes prioritize high T_g (≥ 150–170 °C) materials with high thermal decomposition temperature (T_d) and low Z-axis CTE; final selection depends on the reflow profile and reliability metrics. Standard FR4 has a K value of approximately 0.4 W/m·K, while high-performance laminates can achieve higher K values (> 1 W/m·K).

> Recommend reading: High TG PCBs

4.3.2 CTE Matching and Metal Core Boards

For high-power printed boards, choose a substrate with a Coefficient of Thermal Expansion (CTE) that matches the component carrier material, or use a metal core printed board.

Note on Metal Core PCBs (MCPCB): The metal core (Al/Cu) has high thermal conductivity (approx. 200/400 W/m·K), but the thermal bottleneck is the insulating dielectric layer above it; selection should focus on dielectric thickness and K value.

V. External Cooling and Advanced Thermal Solutions

Beyond PCB optimization, high-power systems must incorporate specialized external cooling hardware and materials.

5.1 Heat Sink Integration and Connection

Using thermal interface materials is intended to reduce thermal resistance during the conduction process, applying them at the contact surface between high-power components and the substrate to improve heat transfer efficiency.

5.1.1 Heat Sink Layout and Mounting

High heat-generating components should not be directly surface-mounted but should be paired with an external heat sink or heat spreader. Components with high heat or current should, whenever possible, be mounted onto a heat sink, kept away from other components, and ensured an unobstructed thermal path. Heat sink materials should be chosen based on high thermal conductivity, typically aluminum or copper. Power components like switching tubes and diodes should contact the heat sink as reliably as possible.

5.1.2 Thermal Interface Material (TIM) Application and Challenges

To minimize thermal resistance between the component body and the heat sink, thermal grease may be applied when necessary.

Power Module Cooling: For small, high heat-generating power modules, the component's grounded casing can be brought into contact with the module's metal casing via thermal grease for heat dissipation.

Soldering Challenges: A common method is attaching the component's metal case directly to the heat sink, but this often results in high thermal resistance. Alternatively, solder paste can be used to directly solder the device onto a metal plate to improve contact reliability and reduce thermal resistance. However, this requires very high quality welding processes, as residual air bubbles at the interface (detectable via CT scan) can lead to a sharp increase in thermal resistance, making this method less common.

> Recommend reading: IPC-J-STD-001: Top Guide to the Latest IPC Soldering Standards (J Revision)

TIM Selection: TIM selection depends on roughness/assembly tolerance/rework requirements and electrical insulation needs: thermal pads/phase change materials/gels/solder each have their appropriate domain. Using thermal paste is one of the most common methods today for reliably securing components to a heat sink, ensuring reliable contact and reducing thermal resistance. In selecting TIM, one must consider not only thermal conductivity (K) but also mechanical properties, electrical characteristics, and temperature stability.

5.2 Heat Pipe Technology and Extreme Environment Solutions

5.2.1 Heat Pipe Technology: Long-Distance Heat Transfer

For extra-high power devices, heat pipe technology (similar to a refrigerator's cooling tubes) can be utilized to cool the component body via conduction. Heat pipes rapidly transport large amounts of thermal energy from the evaporator end to the condenser end through the phase change cycle (vaporization and condensation) of an internal working fluid.

For printed boards operating in high vacuum conditions, where convection is absent due to lack of air, heat pipe technology is an effective cooling solution.

5.2.2 Layout Considerations for Low-Temperature Environments

For boards operating long-term in low-temperature environments, appropriate heating measures should be taken based on the degree of low temperature and the component's operational temperature requirements. This may involve reserving space in the layout for active heating elements.

VI. Conclusion, Recommendations, and NextPCB's Engineering Advantage

A. Core Thermal Design Principles

• Proactive Thermal Modeling is Essential: Design work must begin with pre-layout thermal simulation, determining component heat generation levels and heat flow paths, and establishing non-negotiable layout constraints based on this. Designers must control the internal maximum temperature rise, ensuring the shortest heat transfer path and the largest heat transfer cross-section. It is recommended to perform at least one pre-layout 0D/1D thermal estimation + 3D CFD coarse-mesh iteration, followed by calibrating the simulation coefficients using thermal imaging and spot temperature measurements on EVT prototypes.
• Convection Optimization Relies on System Architecture: The layout must align with the final product's cooling strategy. High heat source positioning must be balanced via CFD/testing, not rigidly placed downstream. The key is to arrange components longitudinally (natural convection, Figure 12-2(a)) or laterally (forced convection, Figure 12-2(b)) and avoid airflow short circuits, ensuring the cooling medium effectively flows through all hot zones.
• High Reliability Requires Strict Isolation: Thermal isolation specifications must be strictly followed, especially for electrolytic capacitors highly sensitive to temperature. Isolation distance should be derived backward from the capacitor case temperature limits and verified through CFD/measurement. As shown in Figure 12-1, the optimized layout (b) results in a significantly lower temperature rise compared to the sub-optimal layout (a).
• Copper Features Maximize Conduction: At the microscopic level, significant thermal resistance reduction is achieved by using heavy copper (2 oz or 3 oz) as a heat spreading plane on internal layers, and high-density, filled thermal vias beneath critical heat sources. Additionally, follow the PCB manufacturer's copper balancing specification to enhance cooling and minimize warping.
• TIM and Heat Sinks are the Ultimate Tools: For high-power components requiring external heat sinks, placement must prioritize proximity to the board edge and mounting points to shorten the conduction path. Heat sinks should be made of high-conductivity aluminum or copper, and the appropriate TIM form should be selected based on assembly requirements and roughness to ensure reliable contact between components and the heat sink.

B. NextPCB's Advanced Manufacturing Capabilities for Thermal Performance

>> More PCB Capabilities at NextPCB.

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About the Author

Arya Li, Project Manager at NextPCB.com

With extensive experience in manufacturing and international client management, Arya has guided factory visits for over 200 overseas clients, providing bilingual (English & Chinese) presentations on production processes, quality control systems, and advanced manufacturing capabilities. Her deep understanding of both the factory side and client requirements allows her to deliver professional, reliable PCB solutions efficiently. Detail-oriented and service-driven, Arya is committed to being a trusted partner for clients and showcasing the strength and expertise of the factory in the global PCB and PCBA market.

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