How to Design FCT Fixtures in PCBA Processing? Development Process and Cost Control

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In PCBA (Printed Circuit Board Assembly) processing, FCT (Functional Circuit Test) is the final checkpoint before delivery. It verifies whether the PCBA functions normally by simulating the product's actual operating environment. The core of FCT testing is the FCT fixture. Many customers have little knowledge about the design, development process and cost of FCT fixtures. Today, C-alley will explain these details for you in depth.



I. What is an FCT Fixture?
An FCT fixture is a customized testing tool used to connect the PCBA to testing instruments. It contacts test points on the PCB via probes to power the board, input stimulus signals, measure output responses, and automatically judge whether the functions are qualified. A complete set of FCT fixture includes: mechanical structure (base and pressing plate for fixing PCBA), probes and connecting wires, control circuit (relays, signal conditioning), and testing program (running on upper computer or single-chip microcomputer).

II. FCT Fixture Development Process
Step 1: Requirement Analysis The customer provides product specifications, schematic diagrams, and normal operating procedures. C-alley confirms key test items with the customer: input voltage range, output load capacity, communication protocols (I2C, SPI, UART, etc.), indicator light status, key response, etc.

Step 2: Scheme Design Design the test circuit (signal generator, electronic load, data acquisition); plan test steps (power-on self-test → input stimulus → measure response → judge result → power-off); determine the structure of the test fixture (pneumatic or manual, probe layout).

Step 3: Fixture Fabrication Process mechanical parts (base plate, pressing plate, probe plate); install electrical parts (connectors, relays, indicator lights, control board); burn the testing program.

Step 4: Program Development and Debugging Write testing software (LabVIEW, C# or embedded C); debug the program with standard samples and optimize test parameters (delay time, judgment threshold). The testing programs of C-alleysupport barcode scanning, data recording and MES (Manufacturing Execution System) upload.

Step 5: Acceptance and Delivery Verify the stability of the FCT system with small-batch products (the false judgment rate should be less than 1%); provide operation instructions, maintenance manuals and calibration methods.

III. Core Components of FCT Fixture
①　Probes: Metal pins that contact PCB test points. Common brands include INGUN, QA, etc. The service life of probes is usually 100,000-200,000 times, and they need to be replaced regularly. C-alleyselects appropriate probes (pointed tip, crown tip, three-claw tip) according to the size and shape of test points.
②　Guiding and Positioning: Use locating pins or frames to fix the PCBA precisely in the fixture with an error ≤ ±0.1mm.
③　Pressing Mechanism: Pneumatic or manual pressing method to press the PCBA tightly on the probes. Pneumatic fixtures have adjustable pressure and stable pressing, suitable for batch testing.
④　Control Box: Built-in relays, power supplies, acquisition cards, etc., which are the electrical core of FCT.

IV. Cost Composition of FCT Fixture
The cost of FCT fixture mainly consists of the following parts for reference:
①　Machining Fee: Machined parts such as base plate, pressing plate, probe plate, about RMB 500-2000.
②　Probes and Wires: Each probe costs RMB 10-30, and a board may need 20-100 probes, totaling RMB 200-3000.
③　Electrical Components: Relays, power supplies, connectors, control boards, etc., about RMB 500-2000.
④　Software Development Fee: Testing program development, about RMB 1000-3000.
⑤　Assembly and Debugging Fee: Manual assembly and debugging, about RMB 500-1500.

The total cost of a set of FCT fixture is usually between RMB 3000-10000, and may be higher for complex products. Although the initial investment is not low, when amortized to each board during mass production, the cost becomes very low. C-alley will optimize the fixture design according to the number of test items to control costs while ensuring coverage.

V. How to Reduce FCT Fixture Cost?
①　Streamline Test Items: Only test core functions, and non-critical functions can be guaranteed by design. Reduce the number of test points to cut down the number of probes.
②　Standardized Design: Use universal control boxes and software frameworks, only need to modify the probe plate and testing program. C-alleyhas accumulated a variety of standard FCT solutions, which can quickly adapt to new products.
③　Replace Pneumatic with Manual: In small-batch or prototyping stages, manual pressing can be used instead of pneumatic fixtures, reducing the cost by more than 50%.
④　Reuse Fixtures: Try to design compatible test point layouts for products in the same series, so that one set of fixture can test multiple types of boards.

VI. Maintenance of FCT Fixture
①　Daily Maintenance: Check whether the probes are bent or dirty in each shift; verify probe contact with an empty board before testing; clean the fixture surface with an anti-static brush.
②　Regular Replacement: Replace probes every 100,000-200,000 times; replace relays according to their service life; replace locating pins of the fixture in time when they are worn.
③　Calibration: Verify the FCT system with standard samples every month to confirm test accuracy. C-alleyestablishes maintenance files for FCT fixtures and conducts regular calibration and maintenance.

VII. FCT Capabilities of C-alley
C-alley has a professional FCT development team that can complete the whole process from requirement analysis, circuit design, software programming to fixture processing. We have developed FCT systems for various products such as power supplies, motor controls, communications, and sensors. Upon delivery, we provide complete operation documents and calibration methods, and can train customer employees to use the system.



VIII. Summary
FCT fixture is the core tool for PCBA functional testing, and its development process includes requirement analysis, scheme design, fixture fabrication, program debugging, and acceptance and delivery. The cost of a set of fixture is usually between RMB 3000-10000, and costs can be reduced by streamlining test items, standardized design, manual pressing, etc. If you need to develop an FCT testing system for your product, please contact C-alley, and we will provide professional scheme design and preferential quotes.

With 17 years of expertise in PCBA design, manufacturing, and service, KingshengPCBA is ready to help turn your ideas into reality. Feel free to contact us anytime to discuss your requirements and get a professional quotation.