3.5 Box Build and System Integration

Mechanical Integration

The PCBA is installed into its chassis or enclosure.

Torque Control: Electric screwdrivers with calibrated torque sensors are used to prevent stripping plastic bosses or cracking the PCB. Torque data is often logged for traceability.
Ruggedization: Applications of adhesives (Loctite), silicones, or Potting Compounds (epoxy resin) are used to seal the electronics against moisture and vibration.
Cable Routing: Internal harnesses are routed and secured to prevent pinching or rattling during transit.

The hardware is inert silicon until the software is injected.

Flashing: The firmware binary (Hex/Bin file) is loaded into the microcontroller.
Serialization: A unique identity (MAC Address, Serial Number) is assigned to the device. This creates the "Digital Birth Certificate" of the unit in the database.
Padding: Binary files are often "padded" with 0xFF or 0x00 to fill unused memory space, ensuring the file checksum is deterministic for verification.

Unlike ICT, which checks component values, FCT checks system behavior.

The Test: The device is powered on and subjected to real-world stimuli (buttons pressed, screens checked, sensors activated).
The Gate: FCT is the final "Go/No-Go" gate. A unit that passes FCT is deemed ready for the customer.

The "Out-of-Box Audit" (OBA) simulates the customer experience.

Cosmetic Inspection: Checking for scratches, gaps, or printing errors on the enclosure.
Packaging: Verification of accessories, manuals, and labels.