The Growing Importance of Thermal Management
CoWoS (Chip-on-Wafer-on-Substrate) packaging has become a dominant approach for high-performance computing, AI accelerators, and high-bandwidth memory modules. The main focus often falls on interconnect density, chiplet integration, or logic-node scaling. However, one of the most critical factors that ultimately limits performance is thermal management.
As power densities continue to rise, traditional cooling solutions like heat sinks, fans, or liquid cooling are no longer sufficient. The materials used within the package—interposers, substrates, and heat spreaders—play an increasingly central role. Among emerging materials, carbon-based solutions and wide-bandgap semiconductors have attracted attention, with SiC substrate (silicon carbide substrate) showing unique potential due to its high thermal conductivity, mechanical robustness, and thermal stability.
The CoWoS Thermal Path: Understanding the Challenge
A CoWoS package consists of multiple layers through which heat must travel. Heat generated by active dies first spreads laterally through the interposer, then moves vertically through the substrate, and finally reaches the external cooling system. Each layer introduces thermal resistance, which can lead to hotspots if not properly managed.
In traditional silicon-based CoWoS, the interposer conducts heat moderately well, but thickness and material limitations restrict its effectiveness. As chiplet architectures become denser, hotspots increase, and thermal gradients can cause mechanical stress. In such conditions, materials like SiC substrate can enhance lateral heat spreading and reduce the risk of thermal-induced deformation, bridging a critical gap in system-level thermal management.
Silicon Interposers: Strengths and Limitations
Silicon interposers are widely adopted in CoWoS due to their mature fabrication processes, fine-pitch interconnect compatibility, and electrical performance. For low- to moderate-power applications, silicon interposers work well, providing precise signal routing and mechanical support.
However, as CoWoS scales to high-power applications, limitations become evident:
Localized hotspots reduce performance and reliability.
Thermal expansion mismatch between silicon interposer and high-power dies can induce stress and warpage.
Thickness constraints limit the interposer’s ability to dissipate heat effectively.
These challenges illustrate why alternative or complementary materials, such as SiC substrate, are needed to maintain performance and reliability in next-generation CoWoS systems.
Expanding the Thermal Materials Palette
Meeting the thermal demands of high-density CoWoS packaging requires moving beyond silicon. Materials engineers now focus on several approaches:
Advanced Heat Spreaders: Copper or copper-molybdenum composites can reduce local thermal resistance, but they often introduce mechanical mismatch.
High-Performance Thermal Interface Materials (TIMs): Reduce contact resistance, yet cannot overcome fundamental material limits.
Ceramics and Wide-Bandgap Materials: Materials like SiC substrate combine high thermal conductivity with mechanical strength and chemical stability, making them ideal for high-power, high-density CoWoS applications.
By strategically integrating these materials, it becomes possible to create a CoWoS package where each layer has a clearly defined role in thermal management rather than relying solely on external cooling.
Silicon Carbide Substrate: Functional Roles in CoWoS
SiC substrate offers several advantages over conventional silicon for thermal management in CoWoS packages:
High Thermal Conductivity: Facilitates lateral and vertical heat spreading, minimizing hotspots.
Low Coefficient of Thermal Expansion (CTE): Reduces mechanical stress during thermal cycling.
Mechanical Robustness: Maintains dimensional stability in thin and large-area wafers.
Chemical Stability: Compatible with aggressive high-temperature processing and long-term operation.
In practical applications, SiC substrate can serve multiple roles:
As a high-performance interposer, replacing or complementing silicon layers.
As an embedded heat-spreading layer beneath high-power dies.
As a structural layer to stabilize the package and prevent warpage under thermal stress.
These roles allow the interposer and substrate to function as a unified thermal and mechanical platform, not just as an electrical interconnect layer.
System-Level Implications of Thermal Materials
Thermal management materials influence more than heat dissipation—they determine overall system architecture. By incorporating SiC substrate or similar advanced materials, designers can achieve:
Higher sustained performance under continuous high-power operation.
Reduced thermal gradients, improving reliability and reducing failure rates.
More compact multi-chip modules and heterogeneous integration, enabling innovative designs in AI accelerators and high-performance computing.
In other words, thermal materials now act as enablers rather than constraints. Decisions made at the materials layer influence package layout, chiplet placement, and ultimately, the performance of the entire system.
Manufacturing Considerations for SiC Substrate in CoWoS
While SiC substrate offers significant advantages, its integration into CoWoS packages requires careful consideration:
Wafer Thinning: SiC is harder than silicon, making precision thinning challenging.
Via Formation: Through-SiC vias require advanced etching or laser-assisted methods.
Metallization: Achieving strong, reliable metal adhesion on SiC requires barrier and adhesion layers tailored to high-temperature operation.
Defect Control: Large-area SiC wafers for 12-inch CoWoS must maintain uniformity and low defect density to ensure yield.
These challenges are non-trivial but surmountable. Solutions in process control, inspection, and material handling enable the use of SiC substrate in high-performance CoWoS applications.
Towards Material-Centric CoWoS Architectures
The evolution of CoWoS suggests that advanced packaging will increasingly be material-driven. Electrical connectivity remains important, but thermal and mechanical properties now play an equally critical role. By integrating SiC substrate, CoWoS packages can support higher power densities, reduce risk of thermal failure, and enable complex heterogeneous integration architectures.
This shift also highlights a broader trend in semiconductor packaging: materials science, mechanical engineering, and system-level design are converging. Future CoWoS packages will be defined as much by the choice of thermal materials as by interconnect pitch or die size.
Conclusion
CoWoS thermal management materials are no longer peripheral—they define the operating envelope of modern high-performance systems. Traditional silicon layers are reaching their thermal limits, and innovative materials like SiC substrate provide new pathways for heat spreading, mechanical stability, and long-term reliability.
By prioritizing material-level innovation and integration, CoWoS designers can unlock higher performance, denser architectures, and robust operation in demanding environments. As power densities continue to rise, SiC substrate will become a key enabler of next-generation CoWoS technology, bridging the gap between material science and system-level performance.
The Growing Importance of Thermal Management
CoWoS (Chip-on-Wafer-on-Substrate) packaging has become a dominant approach for high-performance computing, AI accelerators, and high-bandwidth memory modules. The main focus often falls on interconnect density, chiplet integration, or logic-node scaling. However, one of the most critical factors that ultimately limits performance is thermal management.
As power densities continue to rise, traditional cooling solutions like heat sinks, fans, or liquid cooling are no longer sufficient. The materials used within the package—interposers, substrates, and heat spreaders—play an increasingly central role. Among emerging materials, carbon-based solutions and wide-bandgap semiconductors have attracted attention, with SiC substrate (silicon carbide substrate) showing unique potential due to its high thermal conductivity, mechanical robustness, and thermal stability.
The CoWoS Thermal Path: Understanding the Challenge
A CoWoS package consists of multiple layers through which heat must travel. Heat generated by active dies first spreads laterally through the interposer, then moves vertically through the substrate, and finally reaches the external cooling system. Each layer introduces thermal resistance, which can lead to hotspots if not properly managed.
In traditional silicon-based CoWoS, the interposer conducts heat moderately well, but thickness and material limitations restrict its effectiveness. As chiplet architectures become denser, hotspots increase, and thermal gradients can cause mechanical stress. In such conditions, materials like SiC substrate can enhance lateral heat spreading and reduce the risk of thermal-induced deformation, bridging a critical gap in system-level thermal management.
Silicon Interposers: Strengths and Limitations
Silicon interposers are widely adopted in CoWoS due to their mature fabrication processes, fine-pitch interconnect compatibility, and electrical performance. For low- to moderate-power applications, silicon interposers work well, providing precise signal routing and mechanical support.
However, as CoWoS scales to high-power applications, limitations become evident:
Localized hotspots reduce performance and reliability.
Thermal expansion mismatch between silicon interposer and high-power dies can induce stress and warpage.
Thickness constraints limit the interposer’s ability to dissipate heat effectively.
These challenges illustrate why alternative or complementary materials, such as SiC substrate, are needed to maintain performance and reliability in next-generation CoWoS systems.
Expanding the Thermal Materials Palette
Meeting the thermal demands of high-density CoWoS packaging requires moving beyond silicon. Materials engineers now focus on several approaches:
Advanced Heat Spreaders: Copper or copper-molybdenum composites can reduce local thermal resistance, but they often introduce mechanical mismatch.
High-Performance Thermal Interface Materials (TIMs): Reduce contact resistance, yet cannot overcome fundamental material limits.
Ceramics and Wide-Bandgap Materials: Materials like SiC substrate combine high thermal conductivity with mechanical strength and chemical stability, making them ideal for high-power, high-density CoWoS applications.
By strategically integrating these materials, it becomes possible to create a CoWoS package where each layer has a clearly defined role in thermal management rather than relying solely on external cooling.
Silicon Carbide Substrate: Functional Roles in CoWoS
SiC substrate offers several advantages over conventional silicon for thermal management in CoWoS packages:
High Thermal Conductivity: Facilitates lateral and vertical heat spreading, minimizing hotspots.
Low Coefficient of Thermal Expansion (CTE): Reduces mechanical stress during thermal cycling.
Mechanical Robustness: Maintains dimensional stability in thin and large-area wafers.
Chemical Stability: Compatible with aggressive high-temperature processing and long-term operation.
In practical applications, SiC substrate can serve multiple roles:
As a high-performance interposer, replacing or complementing silicon layers.
As an embedded heat-spreading layer beneath high-power dies.
As a structural layer to stabilize the package and prevent warpage under thermal stress.
These roles allow the interposer and substrate to function as a unified thermal and mechanical platform, not just as an electrical interconnect layer.
System-Level Implications of Thermal Materials
Thermal management materials influence more than heat dissipation—they determine overall system architecture. By incorporating SiC substrate or similar advanced materials, designers can achieve:
Higher sustained performance under continuous high-power operation.
Reduced thermal gradients, improving reliability and reducing failure rates.
More compact multi-chip modules and heterogeneous integration, enabling innovative designs in AI accelerators and high-performance computing.
In other words, thermal materials now act as enablers rather than constraints. Decisions made at the materials layer influence package layout, chiplet placement, and ultimately, the performance of the entire system.
Manufacturing Considerations for SiC Substrate in CoWoS
While SiC substrate offers significant advantages, its integration into CoWoS packages requires careful consideration:
Wafer Thinning: SiC is harder than silicon, making precision thinning challenging.
Via Formation: Through-SiC vias require advanced etching or laser-assisted methods.
Metallization: Achieving strong, reliable metal adhesion on SiC requires barrier and adhesion layers tailored to high-temperature operation.
Defect Control: Large-area SiC wafers for 12-inch CoWoS must maintain uniformity and low defect density to ensure yield.
These challenges are non-trivial but surmountable. Solutions in process control, inspection, and material handling enable the use of SiC substrate in high-performance CoWoS applications.
Towards Material-Centric CoWoS Architectures
The evolution of CoWoS suggests that advanced packaging will increasingly be material-driven. Electrical connectivity remains important, but thermal and mechanical properties now play an equally critical role. By integrating SiC substrate, CoWoS packages can support higher power densities, reduce risk of thermal failure, and enable complex heterogeneous integration architectures.
This shift also highlights a broader trend in semiconductor packaging: materials science, mechanical engineering, and system-level design are converging. Future CoWoS packages will be defined as much by the choice of thermal materials as by interconnect pitch or die size.
Conclusion
CoWoS thermal management materials are no longer peripheral—they define the operating envelope of modern high-performance systems. Traditional silicon layers are reaching their thermal limits, and innovative materials like SiC substrate provide new pathways for heat spreading, mechanical stability, and long-term reliability.
By prioritizing material-level innovation and integration, CoWoS designers can unlock higher performance, denser architectures, and robust operation in demanding environments. As power densities continue to rise, SiC substrate will become a key enabler of next-generation CoWoS technology, bridging the gap between material science and system-level performance.
