🔍 What is FCT (Functional Circuit Test)?

FCT is a black-box test that simulates the operational environment of the PCB and verifies its electrical, functional, and software behavior. Unlike ICT, which tests individual components and nets, FCT validates the entire system functionality.

✅ Step-by-Step FCT Process

Step 1: Setup of FCT Environment

• A test jig or fixture is prepared with:

  • Power supply connectors

  • Communication ports (USB, UART, CAN, Ethernet, etc.)

  • Signal injection and measurement points

  • Load simulators or actual end-user devices

• The test software is loaded onto the PC/test station

Step 2: Loading the DUT (Device Under Test)

• The PCB assembly is placed into the test fixture.

• Proper alignment and contact with pogo pins, clamps, or interface connectors are ensured.

Step 3: Power-On and Initialization

• The tester powers up the DUT.

• Checks for:

  • Proper power-up sequence

  • No over-current/over-voltage conditions

  • Boot-up of embedded firmware (if any)

Step 4: Communication Interface Testing

• Tests performed:

  • UART, I2C, SPI, USB, Ethernet communication

  • Wireless interfaces (Bluetooth, Wi-Fi, Zigbee) if applicable

  • Microcontroller or processor boot logs are captured and checked

Step 5: Functional Test Execution

Each feature or function of the PCB is tested as per test plan:

• Input/output signal verification

• Relay or actuator control check

• Analog/digital signal processing

• Audio/video playback (if applicable)

• Display and indicator LED check

• Button and switch detection

• Firmware functionality (menu flow, logic, timing)

Step 6: Measurement and Data Capture

• Instruments like multimeters, oscilloscopes, signal generators, and analyzers record data.

• Any parameter deviation is logged.

Step 7: Software/Firmware Validation

• Check embedded software behavior

• EEPROM or Flash memory write/read test

• Execute any diagnostic firmware commands

Step 8: Pass/Fail Decision

• Based on thresholds and tolerances defined in the test plan

• Visual indication and/or printed labels/stickers applied on passed boards

🧰 Instruments & Equipment Used in FCT

📋 Test Plan (Key Components)

1. Test Objective: Ensure PCB performs required functions.

2. Test Scope: Define hardware, firmware, interfaces to be tested.

3. Test Cases:

   • ID, Description, Steps, Expected Result

   • Example: TC_001: Power ON check → PCB boots within 3s

4. Pass/Fail Criteria: Defined tolerances and acceptable margins

5. Test Environment: Tools, jigs, software needed

6. Test Sequence: Stepwise order of test execution

7. Operator Instructions: Clear guide for test personnel

📝 Test Documentation

✅ Key Benefits of FCT

• Ensures real-world behavior of the board

• Identifies system-level defects not caught in earlier steps

• Ensures firmware and communication reliability

• Increases customer confidence and product quality