PCB Technical - The method of pcb testing

PCB testing is primarily used to mitigate problems throughout the manufacturing process as well as during final production. These types of tests can also be used on prototypes or small-scale assemblies, which helps to identify potential problems that may exist in the final product.

Printed circuit boards (PCBs) are widely used in a variety of electronic devices whether it's a cell phone, a computer, or a complex machine, you can find circuit boards. If a PCB is defective or has manufacturing issues, it can lead to malfunctions and inconvenience in the final product. In these cases, manufacturers will have to recall these devices and spend more time and resources to fix the fault. As a result, PCB testing has become an integral part of the circuit board manufacturing process, identifying problems in a timely manner and assisting staff to deal with them quickly to ensure high quality PCBs.

What PCBs are mainly tested for

Various components of a circuit board can be tested in various PCB test methods.

Lamination

The quality of the lamination in a PCB is a critical component. The peel resistance of the laminate is tested using force or heat. Peeling can lead to significant issues surrounding the final function of the PCB.

Copper Plating

It is important to test the copper plating of the PCB, which is a copper foil laminated to the board. This overlay is electrically conductive and should be tested in detail for quality, tensile strength and elongation.

Solderability

Solderability testing means analyzing the materials on the board to ensure that other components can be securely attached. If the board proves to be unsolderable, the designer cannot confidently connect other necessary components to the board. This test is performed using wetting.

Hole Wall Quality

Hole wall quality testing allows professionals to determine if the walls of the holes will break down or delaminate when the PCB is used. This test typically involves rapid temperature changes to evaluate the PCB's response to a thermally stressful environment.

Electrical.

In order for any PCB to function properly, it must have stable electrical conductivity. Electrical testing will determine this by allowing a current with minimal leakage through the board.

Environmental

Since PCBs typically operate in humid climates, designers must test them for water absorption. Before and after introducing the PCB to a humid environment, the expert will weigh it. If there is a significant change in weight, the PCB has failed.

Cleanliness

Finally, the PCB must be able to withstand a variety of corrosion, moisture, dirt, and other external factors while still functioning properly. An expert will test the PCB and its resistance to a variety of potential environmental conditions and analyze the before and after of each situation.

PCB test methods

1.Manual Visual Inspection of PCBs

The use of magnifying glasses or precision microscopes, relying on the operator's visual assessment to determine whether the quality of the board meets the standard, and decide whether the need for correction. This method has a long history, the advantage of its initial low cost and no test fixture, but limited by the subjectivity of human judgment, long-term cost accumulation, difficult to continuously monitor defects and data collection challenges, with the PCB production surge and component miniaturization, the feasibility of its gradual decline.

2.On-line Electrical Testing of PCBs

Manufacturing defects are identified through electrical performance testing, covering the verification of analog, digital and mixed-signal components to ensure product specifications are met. Existing technologies include bed-of-pins tester and flying probe tester, etc. The advantages are low cost of single-board testing, comprehensive digital and functional testing, rapid and thorough short circuit and open circuit detection, flexible firmware programming, high defect coverage and convenient programming. However, it requires test fixtures, time-consuming programming and debugging, high fixture costs and complex operation.

3.Functional verification of PCB boards

In the middle and late stages of the production process, the use of special test equipment to implement a comprehensive assessment of the functional modules of the circuit board to confirm its performance. This method is based on the early concept of automated testing, for a particular board or unit design, can be realized with the help of a variety of equipment. There are various types, such as end-product testing, prototype testing and stack testing. Although functional testing can provide a macro-assessment, but the lack of in-depth diagnostic data, and equipment-specific, complex test process, programming difficulties, so it is not suitable for large-scale production lines.

4.Automated Optical Inspection (AOI)

Based on optical principles, combined with image analysis, computer and automation technology, the production of defects in the efficient identification and processing, AOI is commonly used before and after the reflow soldering and electrical testing, significantly improve the pass rate of the subsequent test phase, when the cost of correction is much lower than after the final test. Its advantage lies in the early detection and correction of defects, but the technology is relatively new and still needs to be continuously optimized.

5.Automatic X-ray Inspection

The use of X-ray penetrability differences, see through the inspection area, accurate identification of ultra-fine pitch, high-density circuit boards and assembly process of bridging, missing parts, poor alignment and other issues, and even see through the IC chip inside. As a unique means of detecting the quality of BGA soldering, it does not require fixtures, but there are limitations of slow detection, high failure rate, difficult to rework the solder joint detection, high cost and long program development cycle.

6.Laser Scanning Inspection Technology

As the latest progress in the field of PCB testing, this technology utilizes a laser beam to scan the board, collect detailed data and compare it with the preset standards. Its effectiveness has been verified on bare boards, and is being explored for use in assembly board testing at a speed that meets the demands of mass production. Its advantages are fast output, no fixture and visual unobstructed, but the initial investment is large, maintenance and use of more challenges.

7.Dimensional precision measurement

The use of quadratic image measuring machine, accurate measurement of holes, length and width, position and other key dimensions. In view of the thin and light characteristics of PCB, non-contact measurement avoids errors caused by deformation, and becomes the preferred solution for high-precision measurement. Fully automated measurement through programming not only improves measurement accuracy, but also significantly shortens the measurement cycle and improves work efficiency.

PCB testing is an important step in safeguarding the quality of electronic equipment. Ensuring the high quality of circuit boards through a variety of testing methods lays a solid foundation for product stability and reliability.