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ICT Test: Inspection Method for Batch PCBA Projects

In high volume PCB assembly projects, ICT or in-circuit testing is an essential inspection technology that cannot be overlooked. Its primary purpose is to verify the electrical functionality of the circuit at different stages of the production process, as well as prior to full assembly. This proactive approach enables early detection of faults and defects, ultimately saving production costs and minimizing rework time. At FS Technology, we hold ICT testing in high regard as a proven technology that has allowed us to consistently provide our clients with high-quality circuit board production. Let us now delve deeper into the intricacies of ICT testing within the realm of PCBA.

In circuit testing

Advantages and disadvantages of ICT testing

Advantage

  • Excellent Detection Ability: Provides accurate and reliable results for detecting faults such as short circuits, open circuits, and incorrect component connections. Additionally, it can effectively test BGA, which may be challenging to test using other methods.
  • Fast Turnaround: Although the setup process can be complex, utilizing ICT testing PCB during the project can help to identify and address issues early on, reducing the need for rework and repairs and resulting in faster project turnaround times.
  • Easy Program Generation: In-circuit test systems can generate most of the necessary programs directly from the layout files, simplifying the program generation process.
  • Strong Versatility: Test platform supports both Windows and UNIX operating systems, making it versatile and adaptable to a variety of testing environments.
  • Easy Fault Identification: The system generates results for each node, enabling experts to quickly and easily identify fault points and troubleshoot any issues that may arise during testing.

Disadvantage

  • Limitations: ICT is primarily utilized for detecting faults at the component level and may not be suitable for detecting faults at the board or system level. Additionally, it may not be effective for testing analog components or high-density PCBA that power cycle.
  • High Cost: The implementation of testing requires specialized equipment, fixtures, and software, along with regular cleaning and maintenance of test pins, leading to higher upfront costs. As a result, this testing method may not be practical for low-volume projects.
  • Complicated Setup: The setup process for a system is time-consuming and labor-intensive, involving the development of custom fixtures and test programs that are specific to each board layout.
  • Operator Training: Skilled operators are required to troubleshoot any issues that may arise during the testing process, making proper operator training critical.
  • Slower Test Speed: Depending on the complexity of the PCB design and the test method used, in-circuit testing PCB may be slower than other testing processes such as X-ray inspection or AOI inspection.

Types of In-Circuit Testing

  • Bed of Nails (Bon): It is a conventional method of in-circuit testing that utilizes custom-designed fixtures with spring-loaded pins to make connections with the board during testing. The pins make a connection with specific testing points on the board to enable electrical function testing of the PCB. This technique is well-established and provides high throughput and coverage for high-volume production. However, it requires custom fixtures for every board layout, which can be expensive and time-consuming to design and build.
  • Flying Probe: It is a more flexible and adaptable ICT technique that uses non-destructive, fixture-less testing. Instead of a fixed bed of pins, a pair of movable probes make contact with test points on the PCB, enabling access to virtually any location on the board. This technique is less expensive for Small batch PCB assembly, as no custom fixtures are required. However, flying probe testing is generally slower than Bed of Nails and can have lower testing coverage.
 

Each in circuit testing PCB technique has its own features and limitations, and the choice of technique depends on the specific needs of the production process.

ICT Identifiable PCB Defects

  • Short circuits: Rely on the analysis and identification of test parameters such as resistance, capacitance, and inductance to find short circuit problems between two or more conductive components on the circuit board.
  • Open circuits: Testing probes apply a test signal to the circuit at a specific point, and if the expected response is not observed, it indicates an open circuit.
  • Incorrect component values: Predefine the test points and component values before testing, and after the test is completed, we compare the actual values with the expected values to identify any discrepancies.
  • Component polarity and placement issues: Include polarity testing of capacitors, diodes, and polarity-sensitive inductors to identify specific fault points. Additionally, check for misplaced components, broken or bent pins, and incorrect connections, which may result in lower-than-expected resistance values.
  • Missing components: Check the test points of the circuit board to ensure that they receive the expected test signal. If a certain test point fails to receive the signal, it may indicate missing components.
  • Soldering defects: Test for problems such as lack of soldering, virtual soldering, and poor soldering by sending a test signal to the solder joints. If the detection is abnormal, mark the existing problems of the solder joints.

How ICT testing ensures PCBA quality

Composition of Test System

There are three main components to the overall test: Fixtures, Procedures, and Equipment:

  • Test Fixtures: These are custom-designed fixtures that are used to securely hold the board in place during testing, while ensuring access to specific points on the PCB for measurement.
  • Test Procedures: These are a set of instructions that guide the test process and dictate the measurements that are taken during testing. These procedures are designed to ensure that every board is tested accurately and reliably, regardless of its complexity or size.
  • Test Equipment: The hardware we use for testing includes the in-circuit tester itself, digital multimeters, and any additional equipment necessary for measurement and data analysis. This equipment enables us to measure voltage and current at specific points on the board and ensure that the board is functioning as intended.

Equipment Operation Process

  1. Loading the board: The PCB to be tested is loaded onto the test fixture. The fixture is custom-designed for the specific board layout and contains spring-loaded pins that make contact with test points on the board.
  2. Sending test signals: Test signals are sent to the PCB through the bed of nails test fixture. These signals are used to measure the electrical characteristics of the PCB, such as resistance, capacitance, voltage, and other parameters.
  3. Measuring electrical characteristics: The measurements taken during the test are compared to the expected values stored in the test program. The test program is designed based on the board’s design specifications and requirements.
  4. Identifying faults: If the measured values deviate from the expected values, the test equipment identifies the location of the fault on the PCB. This information is then used to determine the type of fault and the appropriate corrective action.
  5. Generating test reports: After the test is complete, a report is generated indicating whether the test passed or failed.

Add In-Circuit Test to PCBA Project

  1. Equipment Selection: Choosing the appropriate equipment is crucial depending on the project stage needs, whether it is for PCBA Prototyping or mass manufacturing. The devices must accurately measure the voltage and current at specific points on the circuit board to provide reliable results.
  2. Fixture Design: After analyzing the PCB design file, the engineer uses CAD software to design a corresponding fixture. The fixture must be manufactured and adjusted to ensure accurate access to specific points on the PCB.
  3. Development Procedure: The engineer must possess expertise in the board and instrumentation used, understanding which parameters must be measured and which procedures must be followed.
  4. Testing Execution: The PCBA company executes and completes the testing process using the developed procedures, testing equipment, and fixtures.
  5. Result Monitoring: The final test results are provided by the service provider to detect potential failures at an early stage and ensure a smooth testing process.
  6. Equipment Maintenance: To ensure consistent performance, existing equipment needs to be regularly calibrated and maintained to remain in good working condition for subsequent projects.

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