Mission Control Board PCBA

DAL-B Autonomous Mission Engine — Lockstep Cortex-R5, 1000 Waypoints, Geofencing, FRAM Storage

Product Overview

The Mission Control Board operates at the highest level of the UAV autonomy stack — above flight stabilization, above navigation, above individual sensor processing — executing the mission-level logic that defines what the aircraft does, when, and why. While a flight controller keeps the aircraft stable and a navigation system knows where it is, the mission control board determines where it should go, what payload actions to perform, and how to respond when mission parameters change. It executes state-machine-based mission scripts, manages waypoint sequences with action triggers (take photo, release payload, begin loiter), monitors geofence boundaries and battery state to autonomously trigger return-to-home, and dynamically re-plans routes in response to pop-up threats, weather changes, or operator re-tasking commands.

The board is built around a safety-certifiable ARM Cortex-R5 lockstep processor running at 400 MHz, chosen specifically for its suitability in DAL-B (Design Assurance Level B) avionics applications per DO-178C/DO-254 guidelines. The dual-core lockstep architecture provides cycle-by-cycle comparison of both cores' outputs, detecting and flagging any computation errors within a single clock cycle — a critical safety feature for autonomous mission execution. The 6-layer PCB isolates the safety-critical computing domain from non-critical interfaces through galvanic isolation on all external I/O, preventing fault propagation. The board supports MAVLink mission protocol with extensions for complex behaviors including servo/payload triggering at waypoints, conditional branching based on sensor thresholds, and parallel mission threads for simultaneous multi-payload operations. An onboard FRAM provides radiation-hardened, corruption-resistant storage for the mission database and configuration parameters, with 10¹⁵ write cycle endurance.

Key Specifications

PCBA Assembly Challenges

Assembling a safety-critical mission control board imposes rigorous process controls beyond those of standard commercial avionics. The Cortex-R5 lockstep processor is typically available in a BGA package (0.8 mm or 0.65 mm pitch) that demands precise solder paste printing with laser-cut stencils and type-4 solder paste. The galvanic isolation components (TI ISO7741 or similar digital isolators) are in SOIC-Wide packages with 1.27 mm pitch; these components have creepage and clearance requirements (minimum 8 mm across the isolation barrier) that must be maintained on the PCB and verified post-assembly — any solder bridge across the isolation gap is a critical defect. The FRAM device is a standard SPI package but is sensitive to electrostatic discharge (ESD Class 1); assembly must be performed on ESD-protected workstations with continuous monitoring. The mission-critical nature of this board demands that all solder joints meet IPC Class 3 criteria, verified by 100% AOI on both sides and X-ray inspection of all BGA and QFN packages. First-article boards undergo cross-sectioning of the isolation barrier region to verify the creepage distance is maintained through all manufacturing steps.

Test Strategy

Each assembled Mission Control Board undergoes an extensive validation sequence with emphasis on safety function verification. The lockstep fault detection is tested by fault injection: a test jig deliberately toggles a single flip-flop in one core and verifies that the lockstep comparator flags the error within one clock cycle and triggers the fault handler. All galvanic isolation barriers are hipot-tested at 5 kV RMS for 60 seconds with leakage current below 1 µA. The mission engine is validated by executing 1000 randomized mission scripts against a golden reference simulator; each script includes waypoint navigation, conditional branches, geofence triggers, and emergency return-to-home sequences. The FRAM is endurance-tested by writing and reading back a known pattern across the full address space for 1000 cycles. All external interfaces (CAN-FD, UART, SPI, I²C) are validated for protocol compliance and error handling. The board undergoes a 72-hour continuous mission simulation with random fault injection every hour; the board must correctly detect all faults and either recover or fail-safe without executing an unsafe command.

PCB Manufacturing Difficulty

The 6-layer PCB for the mission control board is designed with safety isolation as the primary manufacturing challenge. The galvanic isolation barrier requires a minimum 8 mm creepage distance across the PCB surface — achieved with a routed slot (1.0 mm wide) between the isolated domains. The slot must be free of burrs, debris, and copper whiskers that could bridge the isolation gap. The isolated side has its own dedicated ground plane and power plane, completely separated from the non-isolated side's planes by the isolation slot and a minimum 0.5 mm gap on inner layers. The board material is a high-Tg FR-4 (Tg 170°C) with a CTI (Comparative Tracking Index) of ≥400 V to support the isolation requirements. The outer layers use ENIG finish for consistent contact resistance. All isolation-critical dimensions are verified by automated optical measurement on every board before assembly. The FRAM radiation-hardening is achieved at the component level (the FRAM device itself is inherently radiation-tolerant), but the PCB traces to the FRAM are routed on inner layers to provide additional shielding from single-event effects. All boards undergo 100% netlist testing with hipot on all isolation barriers.

More information