The Role of Heatsinks in Server Cooling Systems

Thermal Management Fundamentals in Data Equipment

Servers, routers, and switches all operate under a modular architecture, where components specialize and cooperate. Forced air cooling remains the dominant temperature control strategy and is likely to stay relevant in the near future. Liquid cooling is gaining traction, but current forecasts suggest it will not reach a 50% penetration rate in new data centers until 2025. Key thermal components in air-cooled servers include fans, heatsinks (such as extruded, heat pipe, or vapor chamber models), and thermal interface materials (TIMs).

Heatsinks and CPU Thermal Design

The CPU is the most thermally critical component in a server. x86 processors are still mainstream, though ARM-based options are emerging. Most modern server CPUs consume over 140W, with some exceeding 400W in thermal design power (TDP). Note that TDP reflects the maximum heat that a cooling system can safely manage—not the absolute peak power of the chip.

Server CPUs typically use LGA (Land Grid Array) packaging, which allows easy replacement but requires higher mounting pressure and occupies more vertical space. This constraint limits the room available for heatsink fin structures and forces the use of thicker baseplates to prevent deformation under pressure. As a result, heatsinks in these configurations tend to have reduced fin area and higher airflow resistance.

SOC and High-Power Packaging in Switches and Routers

Unlike servers, switches and routers often use BGA (Ball Grid Array) packaging with lower stress during installation. However, high-end switching chips can also exceed 400W in power consumption, and many manufacturers remove chip lids to reduce junction-to-surface thermal resistance—exposing the bare die to the heatsink.

This bare die configuration creates major challenges for TIM selection. Larger wafers tend to warp, and low-resistance thermal greases struggle to accommodate height variations or adhere to smooth silicon surfaces. TIM 1.5, a material directly bridging the bare die and heatsink, has become a focus of innovation. Ideal TIM 1.5 materials must offer:

· Low thermal resistance

· Strong adhesion and elongation to resist pump-out

· Mechanical resilience across temperature cycles

Promising developments include:

1. Flexible metal pads – High thermal conductivity and strength, though currently limited by poor surface wetting. Surface treatments may significantly reduce interface resistance.

2. Ceramic or metal-core substrates – These better match silicon’s thermal expansion coefficient compared to traditional resin boards, reducing warping.

3. Structural design adaptations – Incorporating high-modulus support elements to absorb thermal stress without deformation.

Memory and Component Heat Mitigation

DIMMs are mounted vertically to maximize server space, but this layout restricts cooling options. As a result, CPU heatsinks are often extended laterally to improve heat dissipation. There are two common designs:

· Upstream extension: Heatsink fins are placed in front of DIMMs, receiving cool air first. This cools the CPU effectively but heats up incoming air for the memory modules.

· Downstream extension: Fins are positioned behind DIMMs, accepting pre-warmed air. This compromises CPU cooling slightly but preserves better airflow for memory.

Striking a balance between CPU and memory thermal needs is a key part of thermal design.

Other components like PCH chips, capacitors, and driver ICs typically have lower heat loads. Their cooling needs are often met with simple extruded heatsinks.

Heatsink Types in Communication Equipment

Three main heatsink types are used across servers, switches, and routers:

1. Heat pipe soldered heatsinks – Ideal for transferring heat from the source to remote fins, making full use of available volume.

2. Extruded aluminum heatsinks – Cost-effective and suitable for moderate power loads.

3. Skived fin heatsinks – Provide a good balance between performance and manufacturability.

High-power servers often use "horn-style" heatsinks, with heat pipes transferring heat from the CPU to extended fins outside the memory zone. However, when chip power exceeds 500W, traditional heat pipe designs may be insufficient due to size constraints. In such cases, advanced solutions like 3D vapor chamber (3D VC) modules are deployed. 

A notable example is NVIDIA’s H100 AI accelerator, with over 700W power consumption, which marked the commercial debut of 3D VC technology at scale

Thermal Risk in Network Infrastructure

Switches and routers facilitate internal data exchange and external network access. Depending on throughput requirements, their form factor and integration levels vary. Like servers, their primary thermal concern is the SOC chip.

A unique challenge in these devices is cooling optical transceivers, which do not lend themselves well to traditional heatsinks due to compact form and poor thermal paths. This has become a bottleneck in high-speed communication hardware.

High-power, rack-mounted routers and switches often use blade-style modules cooled by chassis fans. SOCs in these cases are paired with heat pipe or vapor chamber soldered heatsinks to maintain temperature compliance.

Final Thoughts

Effective cooling design in servers and networking equipment must account for packaging, power density, airflow paths, and mechanical constraints. As power consumption continues to climb, advanced thermal interface materials, packaging strategies, and heatsink designs will be essential to support reliable, high-performance computing infrastructure.

Linda / sales director

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