PCB Thermal Design Case Study for Aluminum Core PCBs

Table of Contents

• I. Introduction: High Power Challenges and the Strategic Role of Aluminum Core PCBs
• II. Aluminum Core PCB Structural Characteristics and Thermal Load Mechanisms
• III. Engineering Model of Conduction Cooling and Heat Flow Path Analysis
• IV. Engineering Case Analysis: Temperature Rise Calculation and Interpretation for a Double-Sided Aluminum Core
• V. Limitations of Core Temperature Rise and Total Thermal Resistance Analysis: The Dielectric Challenge
• VI. Implementation and Manufacturing: NextPCB's Support in MCPCB Design
• VII. Summary and Outlook

I. Introduction: High Power Challenges and the Strategic Role of Aluminum Core PCBs

Modern electronic system design faces unprecedented demands for power density, driven by the trend toward smaller sizes, higher integration, and stable operation in increasingly harsh environments. In this context, the limitations of traditional FR4 PCBs in terms of thermal management design are becoming increasingly evident. Their low thermal conductivity (typically less than 1 W/(m·K)) makes them a bottleneck for system heat dissipation. For high-power applications requiring conduction cooling, heat must be efficiently conducted laterally from the heat-generating components to the cold plate edges. This makes the PCB plane's lateral thermal conductivity crucial.

The Aluminum Core PCB (Metal Core PCB, MCPCB) is a key technology developed precisely to solve this challenge. The core concept of MCPCB is to replace the bulk of the low-conductivity insulating substrate with a highly conductive metal core (such as aluminum or copper), providing a low-impedance path for heat flow. This structure significantly enhances the in-plane thermal spreading capability of the PCB, making it a standard solution in fields such as high-power semiconductors and LED lighting.

This engineering case study focuses on an advanced thermal management structure: a double-sided component mounted PCB featuring an aluminum heat-dissipation core. This design utilizes Surface Mount Technology (SMT) for flat-pack integrated circuits installed on thin circuit layers, which are then bonded to both sides of the central aluminum plate (refer to descriptive Figure 12-8). The goal is to maximize power handling capacity. The design target is to maintain a minimal temperature rise under a total dissipation power of 4.8 W through efficient conduction cooling. Through rigorous engineering calculations and thermodynamic analysis, this article quantifies the thermal performance of this design and discusses its value and limitations in practical applications.

II. Aluminum Core PCB Structural Characteristics and Thermal Load Mechanisms

A. Structural Analysis and Power Density Increase

The aluminum core PCB structure shown in this case represents an advanced design form for high power density applications. It consists of three main functional layers: thin circuit layers on both sides (including dielectric insulation and copper traces), and the highly conductive aluminum core in the middle. Components are mounted on the thin circuit layers using Surface Mount Technology (SMT). This double-sided mounting structure significantly increases system integration.

Due to the aluminum core's excellent thermal spreading capability, this structure can accommodate twice as many integrated circuit components as a PCB with components on only one side, resulting in a total dissipation power double that of a single-sided PCB. In this case, electronic components are mounted on both sides of the board, with 2.4 W of power dissipated by components on each side, totaling 4.8 W for the entire PCB. This design strategy not only addresses space constraints but, more importantly, leverages the symmetric and efficient heat conduction characteristics of the metal core. You can find more details in PCB Thermal Design Basics (1): Substrate Material Selection.

Achieving this complex double-sided bonding structure places high demands on lamination and thermal interface processing. The quality of the bond between the thin circuit layers and the aluminum core directly determines the vertical thermal resistance of heat flow from the component to the metal core. Manufacturing highly reliable multilayer metal core PCBs requires precise control over the thickness and composition of the thin dielectric material and ensuring the integrity of the bonding interface. For example, NextPCB specializes in manufacturing high-reliability metal core PCBs (MCPCBs), offering high-quality lamination processes that ensure low thermal resistance and long-term reliability of the thermal interface material, which is crucial for achieving the efficient 4.8 W heat dissipation target outlined in this case.

B. Uniform Thermal Load and Temperature Rise Characteristics

A key thermodynamic advantage of this design lies in its symmetry and uniform component distribution. If all components have roughly the same power dissipation, the aluminum core PCB will generate a uniform thermal load. This uniform thermal load is the basis for simplified engineering analysis.

In a conduction-cooled PCB, heat flows from the center toward the cooled edges. When the thermal load is uniform, heat conduction across the board follows the classical one-dimensional (1D) conduction model, with a parabolic temperature rise distribution (refer to descriptive Figure II.B.). This means the highest temperature is located at the geometric center of the board (the point with the longest heat flow path), and the lowest temperature is at the edges contacting the system-level cold plate.

This structural symmetry ensures thermal efficiency: although the total power is 4.8 W, the heat is symmetrically split into two paths, 2.4 W per side, flowing uniformly from the center toward both edges. This bidirectional, symmetric heat conduction fundamentally reduces the lateral thermal resistance. By employing sound (i.e., high thermal conductivity) thermal design, the aluminum and copper heat spreaders within the board can conduct a significant amount of heat. Due to the small temperature rise, this design is particularly suitable for high-ambient-temperature environments or applications with stringent reliability requirements.

Figure II.B. Parabolic Temperature Distribution on a Circuit Board with Uniform Heat Load

Source: Adapted from "PCB Design Technology and Practice" (4th ed.), by Zhiwei Huang, 2024, Publishing House of Electronics Industry.

III. Engineering Model of Conduction Cooling and Heat Flow Path Analysis

A. Conduction Cooling Theory and Heat Flow Path

In high-power PCBs, conduction cooling is central, meaning heat transfer occurs primarily through solid media (copper traces, dielectric layers, and the metal core), rather than relying on less efficient convection or radiation.

For the conduction-cooled PCB shown in this case, the heat flow path can be clearly broken down into two stages (refer to descriptive Figure 12-9):

1. Vertical Conduction: Heat first travels vertically through the component package, solder joints, and the thin dielectric insulation layer, entering the highly conductive aluminum core.
2. Lateral Conduction: Once the heat enters the aluminum core, it spreads predominantly along the plane of the board (i.e., laterally) from the center of the heated board toward the edges. The edges are typically in intimate contact with a system-level cold plate or heatsink, where the heat is dissipated.

The focus of this case is precisely the performance of the aluminum core as a "lateral heat conductor" in the second stage.

B. Rigorous Analysis of the Maximum Temperature Rise Equation

To quantify the lateral conduction efficiency of the aluminum core, we use the maximum temperature rise equation (Equation 12-3) for a conduction-cooled flat plate. This equation is derived based on a 1D steady-state heat transfer model, applicable to elongated boards with a uniform heat source and ideal isothermal cooling at the edges.

Δt_max = ΦL / (2λA)

This equation calculates the maximum temperature difference (Δt_max) between the center point of the aluminum core and the edges (the cold plate contact points). A precise interpretation of the physical meaning of its parameters is key to ensuring calculation accuracy:

• Φ (W): Represents the total dissipated power flowing from the board center toward a single edge. In this case, although the total power consumption is 4.8 W, Φ is taken as 2.4 W (the power per side) because the heat is symmetrically conducted toward both edges.
• L (m): The total length of the heat spreader, 76.2 mm (0.0762 m). The maximum heat flow conduction distance is L/2.
• λ (W/(m·K)): The thermal conductivity of the 5052 aluminum core, known to be 144 W/(m·K). Higher conductivity results in lower lateral thermal resistance.
• A (m²): The cross-sectional area of the aluminum core, which is the channel area for lateral heat conduction. The cross-sectional area A here refers to the area perpendicular to the heat flow direction (i.e., from the board center to the edge), calculated as aluminum core thickness × board width. The given value in the case is 1.032 × 10^-4 m².
• Factor 2: The factor "2" in the denominator is critical; it explicitly indicates that the heat flowing out from the center is symmetrically split to both edges for conduction (bidirectional conduction). This effectively halves the thermal resistance from the center to the edge, demonstrating the efficiency of this double-sided cooling structure.

The essence of this formula is the result of integrating all differential thermal resistances along the length L/2. The design rationale is that the designer successfully constructed a low-lateral-thermal-resistance channel by selecting a high λ and a sufficiently large cross-sectional area A, thereby minimizing the temperature rise.

The input parameters used for this calculation are summarized below:

IV. Engineering Case Analysis: Temperature Rise Calculation and Interpretation for a Double-Sided Aluminum Core

A. Precise Calculation of Maximum Temperature Rise (Δt_max)

According to the parameters and formula above, we can now precisely calculate the maximum temperature rise within the aluminum core (center point relative to the edge cold plate) under a total dissipation power of 4.8 W:

Substituting the known data into Equation:

Δt_max = ΦL / (2λA)

Δt_max = (2.4 W) × (0.0762 m) / (2 × (144 W/(m·K)) × (1.032 × 10^-4 m²))

Δt_max = 0.18288 / 0.0297216 K

Δt_max ≈ 6.152 K

B. Engineering Interpretation and Value Assessment of the Result

The calculated result of 6.15 K holds significant engineering value. On a board 76.2 mm long, supporting a high-power load of 4.8 W, the aluminum core material introduces a maximum temperature difference of only approximately 6.15 K. This result strongly confirms the excellent performance of the aluminum heat spreader as a lateral heat conductor. For details on other related thermal design cases, please refer to PCB Thermal Design Case Study: Copper Thickness for Uniform Heat Load.

This extremely low lateral temperature rise directly validates the effectiveness of high-conductivity materials in suppressing the in-plane thermal resistance of heat flow. Designers successfully conducted heat rapidly from the board center to the edges by increasing the thermal conductivity λ and the cross-sectional area A.

In thermal management, a small temperature rise is a key indicator of high reliability. A low Δt_max means the core center temperature is only 6.15 K higher than the edge cold plate temperature. This result leaves sufficient engineering margin for system design. For example, even if the edge cold plate temperature (T_s) reaches 85°C due to environmental factors, the aluminum core center temperature would only be 91.15°C. This makes it easier to keep the junction temperature (T_j) of the components above within the maximum safe temperature specified by semiconductor manufacturers.

Furthermore, because aluminum has a relatively high heat capacity, such a low temperature difference also suggests that the structure has higher stability against transient thermal shock, effectively smoothing out local and temporary temperature peaks. If the 5052 aluminum core (λ=144 W/(m·K)) were replaced with a high-performance pure copper core (λ ≈ 398 W/(m·K)), the theoretical temperature rise could be reduced to approximately 2.2 K. However, a Δt_max of 6.15 K is sufficiently excellent for most applications, making the 5052 aluminum core the optimal economic choice for achieving this thermal performance budget when considering the trade-off between cost, weight, and manufacturing complexity.

V. Limitations of Core Temperature Rise and Total Thermal Resistance Analysis: The Dielectric Challenge

A. Key Warning: Model Limitations and Total Thermal Resistance

While the calculated result of 6.15 K is encouraging, the warning provided in the case must be strictly adhered to:

This calculation result does not include the temperature rise of the thin circuit layer and is only applicable to the aluminum core heat spreader. This marks a critical distinction in engineering analysis.

In practical high-power designs, the most important thermal metric is the component junction temperature (T_j). The system's total temperature rise (ΔT_total) is the sum of the temperature rises generated by all serial thermal resistances from the component junction to the external cold plate (T_s):

ΔT_total = Δt_package + Δt_interface + Δt_dielectric + Δt_{max (core)}

Since we have verified that Δt_{max (core)} is extremely low (only 6.15 K), this indicates that lateral thermal resistance is no longer the primary bottleneck. Therefore, the design focus must shift to vertical thermal resistance, particularly the thermal resistance of the thin dielectric insulating material (Δt_dielectric).

B. The Dominance of Dielectric Thermal Resistance (R_{th, dielectric})

When heat flows from the component junction to the aluminum core, it must pass vertically through the dielectric layer. Although the dielectric layer is extremely thin (typically between 50 μm and 200 μm), its thermal conductivity (λ) is significantly lower than that of the metal core. Even for high-performance thermal polymer dielectrics, their thermal conductivity is usually only between 3 W/(m·K) and 9 W/(m·K). This vertical heat flow bottleneck means that the dielectric layer's thermal resistance R_{th, dielectric} often becomes the dominant contributor to the total thermal resistance in the MCPCB structure. It is widely accepted in the industry that the thermal resistance of the dielectric layer is one of the most critical factors affecting the overall thermal performance of MCPCBs, potentially surpassing the importance of the metal base itself.

Assuming a high-performance dielectric layer provides a thermal resistance of 0.8 K/W, for a single-side power dissipation of 2.4 W, the temperature rise Δt_dielectric generated by the dielectric layer alone could be 2.4 W × 0.8 K/W = 1.92 K. While this may appear lower than the core's lateral temperature rise on a macroscopic view, heat flow is highly concentrated in the local solder pad area of high-power components, making the localized dielectric thermal resistance the critical factor controlling the component junction temperature.

Because the aluminum core's lateral conduction successfully suppresses Δt_{max (core)} so effectively, design optimization to control and minimize R_{th, dielectric} becomes even more crucial. The core of MCPCB design optimization lies in selecting high-conductivity dielectric materials and using the thinnest possible dielectric layer thickness while meeting electrical insulation requirements (such as voltage breakdown). This is a key area of trade-off that electrical engineers and thermal management experts must consider, as detailed in PCB Thermal Design Basics (3): PCB Wiring Layout.

C. Design Optimization and Thermal Path Management

In practical design, engineers must shift their focus from "Is the board hot?" (macroscopic lateral temperature rise) to "Is the component junction temperature too high?" (microscopic vertical temperature rise). The 6.15 K core temperature difference is an indicator of the structure's successful thermal spreading, while the junction temperature T_j is the ultimate metric for reliability.

In addition to the selection and thickness control of the dielectric layer, engineers must also consider thermomechanical stress. Differences in the Coefficient of Thermal Expansion (CTE) exist between the aluminum core, the dielectric layer, and the copper foil. In applications with high thermal cycling or extreme temperature variations, this CTE mismatch can lead to delamination between layers or fatigue failure in component solder joints. Therefore, high-quality bonding processes and the selection of thermal interface materials are necessary to mitigate these stresses.

Regarding component placement, the thermal load should be distributed as uniformly as possible, and it must be ensured that high-power components have the largest possible vertical heat conduction channel beneath them. This aligns with the principles of Component Layout design, although the uniform thermal load assumption in this case has already simplified this challenge.

VI. Implementation and Manufacturing: NextPCB's Support in MCPCB Design

The success of theoretical thermal design, such as the low Δt_max demonstrated in this case, must ultimately be supported by high-quality manufacturing processes. After the lateral conduction problem is solved, controlling vertical thermal resistance becomes the key to achieving a low junction temperature, and this relies entirely on manufacturing capability.

A. NextPCB's Advanced MCPCB Manufacturing Capabilities

NextPCB possesses the professional technology and equipment in the field of metal core PCB manufacturing to translate theoretical thermal performance into highly reliable, practical products.

• High-Conductivity Material Handling and Assurance: Professional manufacturers like NextPCB typically possess the capability to process a variety of high-conductivity metal substrates (such as 5052 aluminum core, 6061 aluminum core, and copper substrates). Their strict material control and processing procedures help ensure that the thermal performance of the metal core board meets design expectations.
• Precision Dielectric Layer Control and Low Vertical Thermal Resistance: Targeting vertical thermal resistance as the main bottleneck, NextPCB focuses on manufacturing thermal interface dielectric layers with ultra-thin thickness and high thermal conductivity. By precisely controlling the dielectric formulation and lamination process, they can effectively reduce R_{th, dielectric} to industry-leading levels. This is vital for ensuring low component junction temperatures and enhancing the overall thermal performance of a 4.8 W system.
• Quality and Structural Reliability Assurance: The structural integrity of high-power MCPCBs faces thermomechanical challenges. NextPCB employs stringent quality control processes, including thermal cycling tests and high-precision non-destructive testing techniques (e.g., Ultrasonic Scanning Acoustic Microscopy (SAT) for detecting delamination between layers), to verify the mechanical stability and thermal interface integrity of the multilayer structure (especially the bonding interface between the aluminum core and the circuit board) under long-term high thermal loads.

Learn Detailed PCB Manufacturing Processes at NextPCB Factory

B. From Design to Mass Production: NextPCB's Engineering Support

Beyond basic manufacturing, NextPCB also provides engineering support throughout the design and mass production phases, helping customers address complex conduction cooling challenges.

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Design engineers can utilize the NextPCB engineering team to assist with more complex 3D thermal simulations. While the 1D model provided a baseline Δt_max estimate for this case, 3D Finite Element Analysis (FEA) can more accurately evaluate the thermal resistance contributions of the dielectric layer, localized hotspots, and component packages, thereby validating the assumptions of the 1D model and optimizing the layout.

NextPCB offers customized high-power solutions that can accommodate the conduction cooling interface requirements shown in this case, ensuring a tight, low-thermal-resistance connection between the PCB edges and the system-level cold plate. This comprehensive service tightly integrates theoretical thermal design with practical manufacturing capabilities, providing a solid foundation for the successful implementation of client projects.

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VII. Summary and Outlook

This engineering case study provided a rigorous analysis and quantitative calculation of the thermal design for an aluminum core PCB. The analysis showed that by using a 5052 aluminum core with a thermal conductivity of 144 W/(m·K) and employing a double-sided component and symmetric conduction structure, the maximum lateral temperature rise of the aluminum core under a total power dissipation of 4.8 W was successfully limited to approximately 6.15 K.

This result strongly affirms the critical role of high-conductivity metal cores in conduction cooling applications and verifies the significant advantage of this double-sided, uniform thermal load design form in achieving high power density and high reliability. Since lateral thermal resistance has been effectively suppressed, the design focus must shift to the vertical thermal resistance between the components and the aluminum core—namely, the thermal resistance of the dielectric layer. Minimizing R_{th, dielectric} becomes the determining factor in ensuring the component junction temperature remains below the safety threshold.

For design engineers aiming for high performance and high reliability in high power density applications, the success of theoretical analysis must be supported by manufacturing precision. Therefore, selecting a partner like NextPCB, which offers professional capabilities and engineering support in metal core PCB manufacturing, precision dielectric layer control, and structural reliability verification, is key to translating theoretical thermal design into stable, high-performance physical products. By combining advanced thermal design principles with cutting-edge manufacturing technology, the growing heat dissipation challenges of modern electronic systems can be effectively addressed.

About the Author

Sylvia Zhang

Sylvia joined NextPCB two years ago and has already become the go-to partner for clients who need more than just boards. By orchestrating supply-chain resources and refining every step from prototype to mass production, she has repeatedly delivered measurable cost savings and zero-defect launches. Consistency is her hallmark: every client, every order, receives the same uncompromising quality and responsive service.

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