Overcoming Design Constraints in 3U VPX Form Factors: Thermal Management

Modern military and aerospace platforms are under pressure to deliver more performance in less space. To meet that demand, engineers turn to modular, open architectures like the 3U VPX form factor. It supports sensor fusion by combining FPGAs, CPUs, and GPUs to process mission-critical data at high speed.

But in systems this compact, performance is only part of the challenge. Size, weight, and power (SWaP) are constant constraints. At the same time, data movement, connectivity, and scalability shape every design decision. Each adjustment affects the entire system, making trade-offs unavoidable.

VPX thermal management, like all form factor thermal management, isn’t just a constraint to overcome. It’s a core design challenge that defines what’s possible.

What are the main thermal management design challenges in 3U VPX form factors?

The demand for data processing in today’s embedded computing environments continues to grow, with common throughput requests reaching hundreds of gigabits per second. The 3U VPX form factor imposes strict mechanical, volumetric, and interface constraints effectively limiting the number of components that can be integrated within its compact 3D envelope while remaining compliant with the VITA 46.0 standard. Physics becomes a limiting factor, as silicon chips, connectors, and other critical components can only be miniaturized to a certain point with current technology.

At the same time, 3U VPX applications require significant processing power and memory density, often in demanding environments. While modern chips offer incredible processing capabilities, they also draw substantial power and generate expansive thermal loads within a relatively small form factor — and that heat needs to go somewhere.

To meet these demands, engineers require specific design choices tailored to successful thermal management within the constraints of the 3U VPX form factor. Choices like:

Material Selection

The VITA 46.0 standard sets the guidelines for the VPX form factor, including 3U and 6U VPX conduction-cooled modules, specifying the thermal interface design and mechanical attachment points to ensure proper heat transfer.

Aluminum alloy frames are commonly used to dissipate heat from internal components located on the circuit card assemblies. While copper is superior from a thermal perspective, it’s too heavy for the entire frame in many applications. Instead, copper can be placed in strategic areas to transfer heat without adding too much weight – optimizing the trade-off between thermal conductivity and module weight.

Another material consideration is the thermal interface material (TIM). Thermal pastes or gap pads are often applied between a chip and the heat frame to improve thermal conductivity. Different TIMs vary significantly in performance and can be very sensitive to pressure and pad thickness. The engineers at New Wave Design hashave experimented with many TIMs and find that those that consistently deliver high performance through large pressure changes work best.

Wedge Locks

Wedge locks secure the thermal interface between the VPX module rails and the chassis. They apply substantial clamping force to the card edges, ensuring solid thermal contact and optimizing heat transfer from the 3U VPX module into the chassis material. Selecting the right wedge lock design is part of balancing thermal performance with cost, size, and mechanical requirements.

Mezzanines

Mezzanines act as “shelves” positioned above the base carrier within a 3U VPX form factor. If thermal management becomes an issue, components can be placed on the mezzanine to space the hottest elements farther apart. The trade-off in this scenario is the need to dissipate heat from the mezzanine components in addition to the carrier board.

Heat Pipes

Heat pipes channel heat away from components, but they come with a spatial trade-off, since they occupy valuable board space and volume. Generally, allocating more space for heat pipes enhances performance but also limits space for other components.

Heat pipes can also increase manufacturing complexity and cost. At New Wave Design, we offer various solutions tailored for different thermal dissipation requirements – with and without heat pipes – to balance performance, cost, and manufacturability.

Strategic Component Placement

Designing within a 3U VPX form factor is like solving a three-dimensional puzzle, where effective thermal management depends on how components and heat sinks are positioned within tight spatial constraints while navigating critical design trade-offs.

For example, where you want to place a component electronically is not always ideal mechanically. A key challenge is the number of voltage rails required by FPGAs, along with the high current requirements of each rail. Multiple voltage regulators need to be selected, with careful attention paid to regulator mechanical size, efficiency, and output current.

Size constraints limit the XYZ footprint, especially when mezzanine cards impose height constraints. Components need to be placed to not only avoid mechanical interference with stacked cards but also to facilitate the proper thermal solution. One approach at New Wave Design is to place “hot” components near the conduction edge of the VPX card, shortening the thermal path to ensure efficient heat transfer.

Cooling Method

While conductive cooling is a reliable method that requires no airflow, alternative thermal management approaches can dissipate significantly more heat. These include air flow-by (AFB), air flow-through (AFT), and liquid cooling. The AFB standard is defined in VITA 48.7, while the AFT standard is VITA 48.8. These are two standards that we highly recommend engineers review and understand in order to consider alternative cooling methodologies, while maintaining compliance within the open architecture framework.

AFT and liquid cooling help manage the thermal demands of the highest performing silicon chips, which consume substantial power. There are trade-offs for both AFB and AFT at the system level, which should also be understood. Ongoing efforts within the standards community aim to refine these cooling approaches with a push for the industry to converge on a unified air flow-through standard.

Simulation and Modeling

By running simulations that model signal, thermal, electrical, and power integrity during product development, engineers can explore design trade-offs in a virtual environment. This approach accelerates development and significantly reduces developmental costs, as it allows prototypes to be built later in the design process to validate functionality and verify that requirements are met. Proper simulation and modeling tools streamline the trial-and-error process and build confidence before fabrication.

One key consideration, however, is the compute power available for running complex simulations. Many simulation tools require significant computing resources to keep run-times manageable, as the ability to increase the complexity of the simulation while still iterating quickly on various scenarios is key to efficiently improving a design. New Wave Design, for example, maintains computing resources specifically selected to maximize simulation performance and ensures team members can access them from anywhere.

We employ three simulation approaches:

• Signal Integrity Analysis: Focuses on high-speed serial channels (16Gbps, 25Gbps, 56G PAM4, etc.). Though this isn’t directly applicable to thermal management, the component placement trade space must balance impacts to signal integrity and thermal management
• Power Integrity Analysis: Involves DC drop analysis
• Thermal Analysis: Determines the best thermal solution to maximize power dissipation within the module

Simulation viewed as virtual prototyping enables rapid iterations, a clear understanding of trade-offs, and consensus on an optimal design – all before moving on to physical hardware testing.

Effective thermal management in the 3U VPX form factor isn’t just about choosing the right materials or adding heat pipes. It requires a systems-level approach that accounts for the ripple effect each design decision can create. From mezzanines to component layout, every choice influences thermal performance. Simulation and modeling tools make it possible to explore these trade-offs early, helping engineers move faster and design smarter. That kind of foresight is key to building reliable, high-performance systems.