What are the methods of pcb testing?

What are the methods of pcb testing?

PCB testing is a crucial step in ensuring the quality and performance of circuit boards, encompassing comprehensive validation from initial checks during the production process to final product quality assurance. This process not only concerns the physical integrity of the circuit boards but also extends to their electrical performance and reliability in real-world applications. In this article, we will focus on various testing methods for PCBs. The specific contents are as follows:

  1. In-Circuit Testing (ICT)

ICT, or In-Circuit Testing, is an indispensable testing equipment for modern PCB manufacturers, known for its robust capabilities. It primarily detects PCBAs’ circuit continuity, short circuits, and faults in all components by contacting the test points laid out in the PCB layout, providing clear indications to the operators.

ICT boasts a wide range of applications, high measurement accuracy, and precise identification of detected issues, making it straightforward for even moderately skilled workers to handle problematic PCBAs. Utilizing ICT can significantly enhance production efficiency and reduce manufacturing costs.

  1. Flying Probe Testing

Flying probe testing, like In-Circuit Testing (ICT), is a well-recognized and effective testing method. Both can efficiently identify production quality issues, but flying probe testing has proven to be a particularly cost-effective way to improve circuit board standards.

In contrast to traditional testing methods that fix testing probes in position, flying probe testing utilizes two or more independent probes to operate without fixed test points. These probes are electromechanically controlled and move according to specific software instructions. Therefore, flying probe testing incurs lower initial costs and can be completed by software modifications without the need to alter fixed structures. In comparison, ICT entails higher initial fixture costs. Hence, for small batch orders, flying probe testing is more economical. However, ICT is faster and less prone to errors than flying probe testing, making it more cost-effective for large batch orders.

  1. Functional Testing

Functional system testing utilizes dedicated testing equipment at the middle and end of the production line to comprehensively test the functional modules of the circuit board to confirm its quality. Functional testing mainly consists of two types: Final Product Test and Hot Mock-up.

Functional testing typically does not provide in-depth data (such as pin locations and component-level diagnostics) to improve processes but requires specialized equipment and specially designed test programs. Writing functional test programs is highly complex, making it impractical for most circuit board production lines.

pcb testing

  1. Automated Optical Inspection (AOI)

AOI employs a single 2D camera or two 3D cameras to capture images of the PCB, which are then compared to detailed schematics of the circuit board. If the circuit board deviates to a certain extent from the schematics, the areas where the circuit board does not match are marked for inspection by technicians. AOI can detect faults promptly.

However, AOI inspection does not power the circuit board and cannot detect issues with all components 100%. Therefore, AOI is usually used in combination with other testing methods, with common test combinations being:

  • AOI and Flying Probe
  • AOI and In-Circuit Testing (ICT)
  • AOI and Functional Testing
  1. X-ray Testing

X-ray testing, also known as X-ray inspection, utilizes low-energy X-rays to rapidly detect issues such as open circuits, short circuits, voids, and solder bridges on the circuit board.

X-ray testing is primarily used to inspect defect boards with ultra-fine spacing and ultra-high density, as well as defects such as bridging, chip absence, misalignment, etc., that occur during assembly. It can also use slice scans to detect internal defects in IC chips. This is the only method for testing the quality of ball grid arrays and solder ball bonding. The main advantage is the ability to inspect BGA solder quality and embedded components without the need for fixed fixtures.

  1. Laser Testing

This is the latest development in PCB testing technology. It scans the printed circuit board with a laser beam, collects all measurement data, and compares the actual measurements with predefined acceptance limits. This technology has been validated on bare boards and is being considered for use in assembly board testing. Its speed is already sufficient for production lines. Its main advantages are fast output, no fixtures required, and clear visual inspection. However, its main disadvantages are high initial costs and maintenance and usage issues.

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  1. Aging Testing

Aging testing refers to the process of conducting corresponding condition reinforcement experiments to simulate the aging of products under various factors involved in real-world usage conditions. The purpose is to test the stability and reliability of products under specific environments.

According to design requirements, the product is placed under specific temperature and humidity conditions for continuous simulation work for 72 hours to 7 days. Performance data is recorded, and the production process is improved accordingly to ensure that its performance meets market demands. Aging testing typically refers to electrical performance testing, and similar tests include drop testing, vibration testing, salt spray testing, etc.

In addition to the above 7 tests, based on product requirements, other test methods will be used to further ensure PCB quality. They are listed below:

  1. Solderability Testing: Ensures surface robustness and increases the chance of forming reliable solder joints.
  2. PCB Contamination Testing: Detects a large number of ions that may contaminate the circuit board, leading to corrosion and other issues.
  3. Microsection Analysis: Investigates defects, opens, shorts, and other faults.
  4. Time Domain Reflectometer (TDR): Identifies faults in high-frequency boards.
  5. Peel Strength Testing: Determines the strength measurement required to peel laminated boards from the panel.
  6. Float Testing: Determines the level of thermal stress PCB holes can withstand.

PCB testing is a comprehensive process involving multiple levels and methods, ensuring strict quality control at every step from production to application. With continuous technological advancements and the expansion of application scenarios, PCB testing will continue to evolve and improve, providing strong assurance for the steady development of the electronics industry.

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