PCB Technical - 7 inspection methods for PCB production by PCB proofing manufacturers

Explain the process of electronic hardware design including hardware requirements scheme, schematic design, PCB design, PCB proofing, PCB manufacturing, UT and integration testing, etc. Among them, in the PCB board processing and manufacturing link, in order to ensure the production quality of the PCB board, the manufacturer usually uses a variety of detection methods for different PCB defects during the production process.

7 commonly used inspection methods for PCB boards
1. Manual visual inspection of PCB board
Using a magnifying glass or a calibrated microscope, using the operator's visual inspection to determine whether the PCB board is qualified or not, and to determine when a correction operation is required, it is the most traditional detection method. However, due to the increase in PCB production and the shrinking of the wire spacing and component volume on the PCB, this method has become increasingly infeasible.
Advantages: low budget cost, no test fixture.
Disadvantages: human subjective error, high long-term cost, discontinuous defect detection, difficulty in data collection, etc.
2. PCB board online test
Find out manufacturing defects and test analog, digital, and mixed-signal components through electrical performance testing to ensure that they meet specifications. There are several testing methods such as bed-of-needle testers and flying probe testers.
Advantages: low test cost for each board, strong digital and functional testing capabilities, fast and thorough short-circuit and open-circuit testing, programming firmware, high defect coverage and easy programming, etc.
Disadvantages: Need to test fixtures, programming and debugging time, high cost of making fixtures, difficult to use, etc.
3. PCB board function test
The functional system test is to use special test equipment in the middle stage and the end of the production line to conduct a comprehensive test on the functional modules of the circuit board to confirm the quality of the circuit board. Functional testing can be said to be the earliest automatic testing principle. It is based on a specific board or a specific unit and can be completed with various equipment. There are types of final product testing, the latest physical model, and stacked testing. Functional testing usually does not provide in-depth data such as foot-level and component-level diagnostics for process improvement, and requires specialized equipment and specially designed test procedures. It is complicated to write functional test programs, so it is not suitable for most circuit board production lines.
4. Automatic optical inspection
Also known as automatic visual inspection, it is based on optical principles, comprehensively using image analysis, computer and automatic control and other technologies to detect and deal with defects encountered in the production of circuit boards. It is a newer method of confirming manufacturing defects. AOI is usually used before and after reflow and before electrical testing to improve the pass rate of electrical processing or functional testing. At this time, the cost of correcting defects is much lower than the cost after final testing, often reaching more than ten times.
5. Automatic X-ray inspection
Using the difference in the absorption rate of different substances to X-rays, see through the parts that need to be tested, and find defects. It is mainly used to detect defects such as bridging, missing pieces, poor alignment, etc., caused by ultra-fine pitch and ultra-high-density circuit boards and assembly processes. It can also use its tomographic imaging technology to detect internal defects of IC chips. It is currently the only way to test the soldering quality of the ball grid array and the blocked solder balls.
Advantages: able to detect the quality of BGA welding and embedded components, no fixture costs.
Disadvantages: slow speed, high failure rate, difficulty in detecting reworked solder joints, high cost and long program development time.
6. Laser detection system
This is the latest development of PCB testing technology. Scan the printed board with a laser beam, collect all measurement data, and compare the actual measurement value with the preset qualified limit value. This technology has been proven on the bare board, and is being considered for assembly board testing, and the speed is sufficient for mass production lines.
Advantages: fast output, no fixture and visual non-covered access are required.
Disadvantages: high initial cost, many maintenance and use problems.
7. Size detection
Use the two-dimensional image measuring instrument to measure the hole position, length and width, position and other dimensions. Since PCB is a small, thin and soft type of product, contact measurement can easily deform and cause inaccurate measurement. The two-dimensional image measuring instrument has become the best high-precision size measuring instrument.
Different inspection methods have their own advantages and disadvantages. Manufacturers will choose appropriate inspection methods for different PCB board types, complexity, defects and other specific conditions to ensure the quality of PCB boards.
Interesting knowledge
Some people say that only after going to university did they know that the green board is called PCB. In fact, not all PCB boards are green, and there are other colors such as black and purple. The green PCB board is because the surface of the board is coated with a "green oil layer", also called a "solder mask", which is used to protect the circuit and prevent short circuits.