How Copper Coin PCB Improves Thermal Dissipation in Power Devices

Introduction: The Thermal Challenge in Power Semiconductors

Power semiconductors such as IGBT, MOSFET, SiC, and GaN devices generate significant heat during operation. As switching frequencies increase and power densities rise, effective thermal management becomes critical to device reliability and performance. Traditional FR4 PCB substrates present inherent limitations in heat dissipation due to their low thermal conductivity of approximately 0.3 W/mK, compared to copper’s 400 W/mK.

Heat must travel through multiple dielectric layers and resin-rich regions before reaching external cooling structures, creating long thermal paths and high thermal resistance. Copper coin PCB technology addresses this thermal bottleneck by embedding solid copper cylinders directly beneath power device mounting areas, creating a direct vertical heat conduction path from the semiconductor junction to the heat sink or chassis.

Copper Coin PCB Thermal Dissipation Principles

Direct Vertical Heat Conduction Path

The fundamental advantage of copper coin PCB thermal dissipation lies in establishing a continuous thermal bridge connecting the component solder pad to the bottom copper layer or external heat sink interface. When embedded within the PCB stackup, the copper coin provides a high-conductivity material spanning the board thickness directly beneath the heat-generating device, enabling rapid heat transfer with copper’s thermal conductivity of 400 W/mK.

Thermal Performance Comparison

In standard PCB designs, heat must conduct laterally through copper traces and vertically through fiberglass-resin composite layers. This circuitous route introduces substantial thermal resistance. While thermal vias also create vertical heat paths, they occupy limited board area and introduce interfaces between plated copper and base material.

A solid copper coin offers superior cross-sectional area for heat transfer and eliminates the air gaps and resin pockets that reduce via array effectiveness. Testing demonstrates copper coin structures achieve 30-50% lower junction-to-case thermal resistance compared to equivalent thermal via designs in power semiconductor applications.

Structural Design of Copper Coin PCB for Efficient Heat Conduction

Embedded Copper Coin Configuration

Embedded copper coins are machined cylinders inserted into cavities within the PCB core material. The coin typically extends through one or more dielectric layers, with its top surface flush with the component mounting pad and its bottom surface contacting a heavy copper layer or direct heat sink interface. This design suits applications where the power device footprint aligns with standard PCB manufacturing capabilities.

Through-Type Copper Coin Structure

Through-type copper coins span the entire PCB thickness, creating an uninterrupted thermal path from component to heat sink. This configuration works well for single-sided power boards where the component mounts on top and the heat sink attaches directly to the bottom. The elimination of internal interfaces minimizes thermal resistance, making it ideal for high-power copper coin PCB thermal dissipation applications.

Multi-Coin Design for Distributed Heat Sources

Power modules containing multiple semiconductor dies benefit from multi-coin layouts. Each coin is positioned beneath an individual heat source, creating parallel thermal pathways that distribute heat evenly across the cooling interface. Typical coin diameters range from 5mm to 25mm depending on device size and power dissipation requirements, with proper spacing to prevent thermal coupling while maintaining board integrity.

Thermal Resistance Reduction in Copper Coin PCB

Thermal Resistance Component Analysis

Thermal resistance in power semiconductor assemblies consists of multiple series components: junction-to-case resistance within the device package, interface resistance at the solder joint, board thermal resistance, and heat sink interface resistance. Copper coin PCB thermal dissipation primarily targets the board thermal resistance component, which often dominates in conventional designs.

Quantified Performance Improvements

Measurements on IGBT modules show copper coin implementations deliver significant thermal advantages:

• Board thermal resistance reduction – From 0.8-1.2 K/W down to 0.3-0.5 K/W for comparable footprints
• Junction temperature reduction – 60-100°C lower operating temperatures for 200W power devices
• Thermal conductance increase – 10-20 times greater than equivalent FR4 substrate thickness
• Overall thermal resistance improvement – 40-60% reduction compared to standard PCB construction

The thermal resistance reduction stems from both increased effective cross-sectional area and elimination of low-conductivity materials in the primary heat path, fundamentally altering thermal resistance distribution within the assembly.

Applications in Power Semiconductor Modules

IGBT Modules for Automotive Inverters

Electric vehicle traction inverters demand reliable copper coin PCB thermal dissipation for IGBT switches handling hundreds of amperes. The direct thermal path allows heat sink sizing based on actual semiconductor limits rather than PCB thermal constraints, optimizing overall inverter package volume and weight while meeting automotive temperature cycling requirements.

SiC MOSFET High-Frequency Converters

Silicon carbide devices operate at elevated temperatures and switching frequencies, concentrating heat in smaller die areas. Copper coin structures positioned beneath SiC MOSFET packages provide the thermal conductance necessary to prevent hot spots while supporting compact layouts. This combination enables power density improvements in server power supplies, solar inverters, and industrial motor drives.

GaN Power Supply Designs

Gallium nitride transistors enable unprecedented miniaturization in switch-mode power supplies. Copper coin PCB thermal dissipation allows GaN devices to maintain their small footprint advantages while ensuring adequate heat extraction. The technology offers a cost-effective solution for mid-power GaN applications where full ceramic construction is not economically justified.

Reliability and Mechanical Benefits of Copper Coin PCB

Enhanced Thermal Cycling Performance

Beyond immediate thermal performance improvements, copper coin PCB structures enhance long-term reliability under thermal cycling conditions. The reduced temperature swings that result from improved heat dissipation directly decrease thermal fatigue stress on solder joints. Testing demonstrates 2-3 times improvement in thermal cycle count to failure for copper coin assemblies compared to conventional designs in accelerated life testing.

Structural Rigidity Advantages

The copper coin’s structural rigidity reduces board warpage during temperature excursions. By creating a stiff vertical structure through the board thickness, the embedded copper coin constrains local deformation around critical component mounting areas. Solid copper coins eliminate the interface degradation that can occur with thermal vias over extended thermal cycling, where differential expansion opens microscopic gaps that increase thermal resistance over time.

Design and Manufacturing Considerations for Copper Coin PCB

Copper Coin Insertion Process Control

Manufacturing copper coin PCB requires precise cavity formation and coin insertion to ensure proper thermal and electrical contact. The coin must sit flush with surrounding copper layers to enable reliable solder joint formation and minimize contact resistance:

• Tolerance control – Within ±0.05mm for consistent performance across production
• Surface preparation – Critical cavity and coin wall preparation for low thermal interface resistance
• Flatness requirements – Ensures optimal solder joint formation and heat transfer

Surface Finish Impact on Thermal Contact

Surface finish selection affects both solderability and thermal contact resistance at the coin-to-component interface. Electroless nickel immersion gold finishes provide excellent flatness and solderability while adding minimal thermal resistance. Organic solderability preservatives offer lower cost but require careful process control to maintain thin, uniform coatings that do not impede heat transfer.

Mechanical Integration Challenges

Copper coin structures create localized stiffness variations within the PCB that must be considered during assembly processing. Proper prepreg selection and lamination parameters prevent void formation around coin perimeters. Designs should include appropriate keep-out zones around coins to prevent copper feature deformation during pressing operations.

Conclusion: Toward High-Reliability Power PCB Design

Verified Thermal and Reliability Advantages

• Shortest thermal path – Direct heat flow from power components to the metal base minimizes junction temperatures and improves steady-state efficiency.
• Lower thermal resistance – Copper coins reduce junction-to-board thermal resistance by approximately 40–60% compared with standard multilayer PCBs.
• Enhanced reliability – Stable heat conduction mitigates solder fatigue and mechanical warpage during repeated thermal cycling.

Relevance in Modern Power Electronics

• WBG device compatibility – Supports high-frequency, high-power-density SiC and GaN semiconductors requiring efficient thermal management.
• Cost-performance balance – Achieves near-ceramic-level heat dissipation without full migration to expensive metal or ceramic substrates.
• Compact thermal design – Enables smaller layouts while maintaining safe operating temperatures for high-power modules.

Design and Manufacturing Insight

• Controlled copper geometry – Optimizing coin thickness, position, and flatness improves vertical heat conduction.
• Surface finish options – Proper plating (Ni/Au, OSP) enhances thermal interface quality and long-term reliability.

Engineering Support

Highleap Electronics provides copper coin PCB solutions designed for demanding power semiconductor applications. Our fabrication capabilities cover both embedded and through-type copper coin structures, ensuring consistent thermal performance and mechanical stability for advanced power module designs.