PCB Testing Methods and Their Inspection Process

No one can guarantee that produced printed circuit boards are 100% error-free unless you are a deity. Hence, incorporating essential PCB testing after the production process is crucial. This ensures that the circuit boards meet quality standards and reliability requirements. Identifying any errors, defects, or malfunctions during the inspection process is imperative for rectification, as even minor issues within a circuit board can prove fatal. To ensure that the circuit boards you use in electronics are of high quality, this article by TechSparks provides a PCB testing guide encompassing common testing methods and their processes.

AOI PCB Inspection

AOI automated PCB inspection

A non-contact automated inspection method, considered indispensable in production lines, is typically employed during inner and outer layer manufacturing as well as component soldering. It can identify issues with components, connections, and solder joints that are not easily visible to the naked eye. The AOI PCB inspection generally follows these steps:

  1. Input design files into the system and configure parameters.
  2. Calibrate the inspection system for optimal circuit image acquisition.
  3. High-resolution cameras capture circuit images.
  4. Process images to enhance clarity.
  5. Inspectors analyze and compare the captured images with the expected images.
  6. Record and output testing reports.

PCB X-Ray Inspection

PCB X-Ray Inspection

When mentioning X-Ray, it is more commonly associated with the medical field; however, it also plays an essential role in circuit board testing. Despite being two distinct domains, their principles are nearly identical. By emitting high-energy X-rays onto the test object, defects and anomalies in the board can be identified. X-Ray test is often employed in high-density circuit boards, such as multilayer PCB and HDI PCB, as it can uncover voids and hidden layer defects that are invisible to the naked eye. The testing process is generally as follows:

  1. Gather necessary items including PCB samples, X-ray source, detectors, etc.
  2. Fix the sample to the testing platform and configure testing parameters such as X-ray energy and exposure time.
  3. The X-ray tube emits a beam of X-rays, which passes through the sample, forming an X-ray image.
  4. Enhance and filter the internal structure image of the circuit board.
  5. Document the results and generate a testing report.

Flying Probe PCB Test

flying probe PCB testing

The probe rapidly moves across the surface of the circuit board, applying test signals to verify the correctness of circuit connections. As customized bed-of-nails fixtures are not required, this method is particularly advantageous for prototypes or small-batch projects. The flying probe testing process is as follows:

  1. Prepare the PCB samples, control system, probes, etc., for testing.
  2. Develop a test program based on the design diagram, determining the test points and sequence.
  3. Secure the sample onto the fixture, ensuring alignment with guide holes.
  4. Set parameters on the flying probe tester, such as test point coordinates, sequence, and test voltage.
  5. Start the testing equipment.
  6. Probes swiftly move to predetermined test points and establish electrical contact to confirm circuit connectivity.
  7. Analyze the collected data and generate a testing report.

PCB Functional Test

PCB function test

Evaluating the performance of a circuit board by simulating its expected functionalities or operations includes assessing both digital and analog signals, power supplies, and communication interfaces. This type of PCB testing, often used during prototype manufacturing, aims to determine the feasibility of the circuit design. The process of functional testing is roughly as follows:

  1. Gain a comprehensive understanding of user requirements.
  2. Define Test Scope, Goals, Environment, and Resources: Based on the requirements, define the scope, objectives, testing environment, and necessary resources.
  3. Develop test cases covering various functional scenarios and operational paths.
  4. Set up software, hardware, and configurations required for testing.
  5. Following the test cases, input test data and execute different functions.
  6. Analyze and compare the results against the expected outcomes.
  7. Compile the findings into a testing report.

Boundary Scan Testing

PCB Boundary Scan Testing

One way to diagnose connection issues and faults in integrated circuits and other electronic components on a circuit board is by adding programmable test logic to the boundary scan chain of component pins. This approach avoids the need for actual signal transmission during testing. It is particularly useful for cases where there is a large number of pins that are difficult to access directly. The PCB boundary scan testing process follows these steps:

  1. Integrate the scan logic into the IC design during the design phase to form the boundary scan chain.
  2. Secure the circuit board and connect it to the scan controller.
  3. Configure the test mode and speed.
  4. Initiate the program, where the controller communicates with the IC through the boundary scan chain and activates the pins.
  5. Analyze the results and generate detailed test reports.

Environmental Testing

Electronic PCB environmental testing

Circuit boards may need to be utilized in various extreme environments, including humidity, high temperatures, and corrosive conditions. If the boards lack sufficient resistance to meet these challenges, it could lead to electrical issues. Therefore, in PCB environmental testing, designers should simulate these conditions based on the upcoming environment to assess performance.

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