Overcoming Design Constraints in 3U VPX Form Factors: Size, Weight, and Power (SWaP)

The push for higher functionality and greater processing capability is testing the limits of 3U VPX design. Defined by the VITA 46.0 Baseline VPX standard and shaped by platform-specific requirements, size, weight, and power (SWaP) constraints continue to challenge engineers tasked with delivering high-performance embedded computing within a tightly restricted footprint.

The challenge grows as FPGA devices evolve — packing in more logic resources, I/O, ARM processors, and AI cores. AMD’s Adaptable Systems on a Chip (ASoC), for example, integrate programmable logic, acceleration engines, large memory banks, and advanced interface technologies into a single, compact package.

To stay ahead, engineers must take full advantage of advances in connector technology, circuit card design, and silicon integration. Engineering around these constraints calls for new thinking at every level — from how signals move through a connector to how processing power is packaged and integrated on board.

Connector Design and Optimization

Connectors are required to get data to and from the backplane and in and out of mezzanine cards – such as FMC+, XMC, QMC, or custom form factors – yet they also consume valuable board real estate.

The solution is to take advantage of advances in connector technology. Modern connectors can handle data speeds of up to 32Gbps using NRZ signaling and even exceed 56Gbps with PAM4, and many offer higher pin densities that enable greater throughput without increasing their physical footprint.

For example, some connector designs double the number of pins within the same footprint. The physical size doesn’t change, but engineers can add more capabilities within the connectors. However, these connectors also create challenges in board routing, as the reduced pitch between pins makes it harder to maintain signal integrity. For a truly SWaP-optimized 3U VPX design, it’s essential to choose connectors that strike the right balance between size, performance, and routability.

Once signal paths are established, engineers must make careful decisions about how to fit the remaining components without affecting layout quality or introducing thermal and production issues.

Circuit Card Complexity

As performance demand increases, so does circuit card complexity. Some board designs now have 20 or more layers, which not only take up valuable volume within the module but also limit available room for components.

Engineers can overcome this challenge by extending the design into the Z-axis to utilize all the volume within the VPX module. When a single PCB cannot accommodate all required components, consider using mezzanine cards – customized if necessary – to offload components and functionality from the base card. Also consider whether any functions are common enough to use an industry standard footprint and pinout, such as XMC, FMC+, or the new QMC.

Additional strategies include selecting low-profile components to conserve space, though keep in mind that doing so could introduce mechanical and thermal design challenges. Also, using low-loss dielectric materials such as Tachyon 100G for PCB stackups allows engineers to increase layer counts while maintaining controlled impedance in a narrower layout.

In SWaP-optimized systems, miniaturizing the form factor at the circuit level is essential to meeting strict size, weight, and power requirements without sacrificing performance.

Routing density and complexity increases as more components are added into the envelope. Stackup creation becomes critical to allow the board to be routed properly while maintaining signal integrity. In addition to utilizing low-loss dielectric materials, multi-lamination PCBs with blind and buried vias can be implemented.

As an example, New Wave Design works closely with PCB fabricators to understand and take advantage of continuously advancing capabilities to produce high-density PCB layouts and get more capability into the same size and weight constraints presented by 3U VPX.

However, dense layouts using multi-lamination PCBs can make it difficult to maintain signal integrity on channels operating at 25Gbps and above. In these high-speed environments, differential signal vias require special attention. Several factors can impact consistent impedance across the channel, including:

• Drill size
• Pad diameter
• Antipad geometry

When designing to IPC-6012 Class 3 standards, these challenges become more complex. Larger pad sizes, paired with matching antipads and ground voids, can significantly increase routing difficulty in high-density layouts.

At New Wave Design, we address these issues through close collaboration with PCB fabricators, meticulous stackup design, and the use of advanced signal integrity tools.

Even with the most optimized board layout, though, performance gains can only go so far without advances in the chips themselves. That’s where silicon technology becomes critical.

Silicon Technology

Leverage advances in silicon technology to maximize processing power without exceeding size and weight constraints. Modern chip families offer higher processing capabilities than ever before, allowing a single VPX module to achieve functionalities that would have required two or three modules in the past.

Silicon vendors are increasing processing capacity within chips. FPGAs that are now SoCs (System on Chips) combine ARM processors and AI cores with programmable logic, and some even integrate ADCs/DACs or high-bandwidth memory into the package. This reduces the number of components that need to be placed on the board and enhances performance per unit area. At New Wave Design, we work closely with component vendors to ensure that we select the smallest components that can meet our customer’s design goals.

Rethinking the Limits of the Form Factor

As mission requirements evolve and hardware footprints continue to shrink, engineers are challenged to deliver greater capability within the same constrained space.

Smart choices in connector design, circuit layout, and silicon integration in the 3U VPX can lead to SWaP-optimized systems that meet these dynamic performance demands. With careful engineering, it’s entirely possible to maximize processing power without exceeding size, weight, and power limits in your form factor.