In order to ensure the production quality of PCB boards, manufacturers have undergone various testing methods during the production process, each of which will target different defects of PCB boards. It can be mainly divided into two categories: electrical testing methods and visual testing methods.

Electrical testing usually uses a Wheatstone bridge to measure the impedance characteristics between each test point, in order to detect all conductivity (i.e. open and short circuits). Visual testing identifies defects by visually inspecting the characteristics of electronic components and printed circuits. Electrical testing is more accurate in finding short circuits or open circuit defects, while visual testing can more easily detect incorrect gaps between conductors. Visual testing is generally conducted in the early stages of the production process to identify defects and carry out repairs as much as possible to ensure the highest product qualification rate.

The commonly used inspection methods for PCB boards are as follows:

1. PCB board manual visual inspection

The most traditional detection method is to use a magnifying glass or calibrated microscope to visually inspect the circuit board by the operator to determine if it is qualified and when calibration is needed. Its main advantages are low upfront costs and the absence of testing fixtures, while its main disadvantages are subjective human error, high long-term costs, discontinuous defect detection, and difficulty in data collection. Currently, due to the increase in PCB production and the reduction in wire spacing and component volume on PCBs, this method is becoming increasingly impractical.

2. PCB board online testing

There are several testing methods available, such as needle bed tester and flying needle tester, to identify manufacturing defects and test analog, digital, and mixed signal components through electrical performance testing to ensure they meet specifications. The main advantages are low testing costs for each board, strong digital and functional testing capabilities, fast and thorough short-circuit and open circuit testing, firmware programming, high defect coverage, and ease of programming. The main disadvantages are the need for testing fixtures, programming and debugging time, high cost of making fixtures, and difficulty in use.

3. PCB board functional testing

Functional system testing is a comprehensive testing of the functional modules of a circuit board using specialized testing equipment in the middle and end stages of the production line, in order to confirm the quality of the circuit board. Functional testing can be said to be the earliest principle of automatic testing, which is based on specific boards or units and can be completed using various devices. There are types such as final product testing, latest physical models, and stacked testing. Functional testing usually does not provide deep data such as pin level and component level diagnostics for process improvement, and requires specialized equipment and specially designed testing processes. Writing functional testing programs is complex, 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 and utilizes various technologies such as image analysis, computer, and automatic control to detect and process defects encountered in production. It is a relatively new method for confirming manufacturing defects. AOI is usually used before and after reflow and before electrical testing to improve the qualification rate of electrical processing or functional testing stages. At this time, the cost of correcting defects is much lower than that of final testing, often reaching more than ten times.

5. Automatic X-ray inspection

By utilizing the different absorption rates of X-rays by different substances, defects can be detected through fluoroscopy of the areas that need to be examined. It is mainly used to detect defects such as bridging, chip loss, and poor alignment that occur during the assembly process of ultra-fine spacing and ultra-high density circuit boards. Its tomography imaging technology can also be used to detect internal defects in IC chips. It is currently the only method for testing the welding quality of ball grid arrays and obstructed solder balls. The main advantage is the ability to detect BGA soldering quality and embedded components without fixture costs; The main disadvantages are slow speed, high failure rate, difficulty in detecting reworked solder joints, high cost, and long program development time. This is a relatively new detection method that needs further research.

6. Laser detection system

It is the latest development in PCB testing technology. It uses a laser beam to scan the printed circuit board, collects all measurement data, and compares the actual measurement values with the preset qualified limit values. This technology has been proven on optical panels and is being considered for assembly board testing. The speed is sufficient for mass production lines. Fast output, no need for fixtures, and visual non covered access are its main advantages; The main drawbacks are high initial costs and numerous maintenance and usage issues.

7. Size inspection

Use the anime image measuring instrument to measure the hole position, length and width, position and other dimensions. Because PCB is a small, thin and soft type product, contact measurement is easy to deform and cause inaccurate measurement. The anime image measuring instrument has become the best high-precision dimension measuring instrument. After programming, the image measuring instrument of Sirui Measurement can achieve fully automatic measurement, which not only has high measurement accuracy, but also greatly shortens measurement time and improves measurement efficiency.