5.1. Firmware & Test Specification (DFT)

A PCBA is effectively inert silicon until programmed; the definition of firmware and test access is as critical as the copper layout. This section mandates the inputs required to enable In-Circuit Test (ICT) and manufacturing provisioning.

Firmware Provisioning

The manufacturing line requires a binary image and a mechanism to verify it.

• File Format: Intel Hex (.hex), Motorola S-Record (.s19), or Binary (.bin).
• Checksum: A definitive checksum (CRC32 or MD5) must be provided for the final image. The programmer will verify the flashed device against this value.
• Padding: Binary files must be padded to the full memory size (0xFF or 0x00) to ensure the checksum is deterministic.

Design for Test (DFT) Access

Automated testing requires physical access to nets.

• Test Points: Must be located on the Secondary Side (Bottom) to allow for a single-sided fixture (lower cost/higher reliability).
• Point Size: Minimum 0.8 mm diameter for standard probes. Spacing minimum 1.27 mm (50 mil) center-to-center.
• Solder Mask: Test points must be free of solder mask (mask opening > pad size).

Fiducials

Machine vision requires alignment marks.

• Global: Minimum 3 fiducials (1.0 mm solid copper circle) located in the corners of the panel rails.
• Local: Required for all Fine Pitch (< 0.5 mm) components (BGA, QFN). located diagonally on the component perimeter.

Final Checklist