Study Examination: Flexible-Stiff Printed Circuit Board Design for a Groundbreaking Headset Display

In a groundbreaking case study, HoloEye Systems, a leading technology firm, was commissioned by the US Air Force to develop a prototype for a binocular holographic waveguide visor display (HWVD) attached to a pilot's helmet. The display presents a heads-up display of instrumentation and digital representations of important data, significantly decreasing the cost, volume, and weight of traditional helmet-mounted displays, replacing bulky optics systems with thin, light-weight, see-through diffractive optics.

### Key PCB Design Challenges

1. Compact Integration of Optical Modules The Liquid Crystal on Silicon (LCOS) display engine and holographic waveguide are miniaturized optical systems requiring highly precise alignment and integration on the PCB. The PCB must accommodate tiny signal traces with minimal electrical noise to preserve image quality and synchronization between the binocular channels.

2. High-Speed Signal Processing LCOS-based HMDs require rapid data transmission between the display controller and the LCOS panel to maintain real-time augmented reality imagery. Designing PCB traces and interconnects that handle high-frequency signals without signal degradation or cross-talk is critical.

3. Thermal Management The LCOS display and associated illumination sources generate heat in a confined space within the helmet. PCB layout needs efficient thermal pathways and possibly heat sinks to avoid temperature-induced drift or damage to optical or electronic components.

4. Power Supply Isolation and Noise Reduction Stable, low-noise power delivery is necessary to prevent flickering or artifacts on the holographic display. PCB design must include power filtering and isolation strategies to separate sensitive analog circuits from noisy digital parts.

5. Mechanical Stability and Helmet Safety The PCB has to fit into the helmet structure, often curved or irregular in shape, requiring flexible or multi-layer PCBs with reliable mechanical fixation while keeping weight minimal for pilot comfort.

### Solutions to PCB Design Challenges

- Multi-layer PCB with Controlled Impedance Using multilayer PCBs with dedicated signal, ground, and power planes helps maintain signal integrity for high-speed LCOS control signals.

- Optimized Trace Routing and Shielding Differential signaling, careful trace length matching, and shielding reduce electromagnetic interference, maintaining binocular image fidelity.

- Thermally Conductive Materials and Heat Spreaders Incorporating thermally conductive layers or heat spreaders in the PCB stack helps dissipate heat away from the LCOS and illumination elements.

- Power Supply Filtering Components Adding LC filters, ferrite beads, and voltage regulators near sensitive components stabilizes power and reduces display noise.

- Mechanical Design Collaboration Close mechanical and PCB design collaboration ensures the PCB’s shape and mounting points conform to helmet ergonomics and safety standards without compromising electronic performance.

In this innovative project, HoloEye Systems employed high-density interconnect techniques, blind and buried vias, and via-in-pads to break out traces from the FPGA and HDMI controller. The final design consisted of three rigid sections: one for the FPGA, DDR3 ICs, and power supply units, one for slower, analog-type components and more power supplies, and one for a small HDMI receiver with multiple possible orientations. The team used Sierra Circuits' PCB Stackup Planner tool to simulate board stack-up and consider different materials. The final board stackup was 10 layers, with the rigid boards using eight layers and the flex section using one layer.

The article discusses a case study about a wearable high-speed board developed for a binocular holographic waveguide visor display attached to a pilot's helmet. While the search results do not provide a detailed technical paper on this exact subject, the general principles of optical waveguide technology replacing bulky lenses are noted in military head-up displays for improved battlefield awareness. These advances translate to helmet-mounted displays requiring miniaturized optics like LCOS, facing the PCB design challenges outlined above.

To ensure the image quality and synchronization between binocular channels, the PCB must incorporate tiny signal traces with minimal electrical noise, making use of an impedance calculator for precise design.
Incorporating controlled impedance into multi-layer PCBs aids in maintaining signal integrity for high-speed LCOS control signals, contributing to real-time augmented reality imagery.
The USAF's interest in holographic displays indicates a trend within the aerospace industry, raising questions about future funding and investment opportunities in this sector.
The finance industry may benefit from similar technologies, such as those employed in the financial sector's data visualization tools for analysts.
Lifestyle brands could leverage waveguide technology for innovative AR experiences, blending fashion-and-beauty products with digital representations and personalized customer experiences.
The food-and-drink industry might integrate holographic displays for interactive recipes, providing an immersive cooking experience at home or in specialized kitchens.
In the real-estate and home-and-garden markets, AR could be used for virtual staging and space planning, revolutionizing the way people shop for homes or redesign their living spaces.
The rapidly evolving technology behind holographic visors has potential applications in data-and-cloud-computing, enabling real-time data analysis and visualization for improved decision-making.
The sports industry, particularly football (soccer in some regions), NFL, or NCAA football, could adopt holographic displays for coaching analysis, player statistics, and even fan engagement.
The compact, lightweight, and adaptable nature of holographic waveguide displays, as demonstrated in this case study, could lead to innovations in the travel sector, offering interactive tourist guides, language translation services, or even on-the-go entertainment during long journeys.

Study Examination: Flexible-Stiff Printed Circuit Board Design for a Groundbreaking Headset Display