The purpose of inspecting PCB boards is to find out PCB board defects and repair them, ensure the production quality of circuit boards, and improve the product qualification rate. At present, PCB board inspection methods can be divided into two categories: electrical testing methods and visual testing methods.
7 commonly used PCB detection methods, as follows:
1. Manual visual inspection
Testing manual visual inspection of PCBs is the most traditional inspection method. It has the advantage of low initial cost and no test fixtures. Determine whether the PCB board is qualified by visual inspection using a magnifying glass or calibrated microscope and determine when correction operations are needed. The disadvantages of manual visual inspection are subjective human error, high long-term costs, discontinuous defect detection, and difficulty in data collection. With the increase in PCB production and the shrinkage of wire spacing and component size on PCBs, manual visual inspection methods are becoming increasingly unfeasible.
2. Dimensional inspection
Use a two-dimensional image measuring instrument to measure the position, length and width of the hole, its location and other dimensions. Since PCB is a thin and soft product, contact measurements can easily deform, resulting in inaccurate measurements. The 2D image measuring instrument has become the best high-precision dimensional measuring instrument. The image measuring instrument can realize automatic measurement after programming. It not only has high measurement accuracy, but also greatly shortens the measurement time and improves the measurement efficiency.
3. Online test
There are several testing methods, such as bed of needles tester and flying probe tester. Conduct electrical performance testing to identify manufacturing defects and test analog digital and mixed-signal components to ensure they meet specifications. The main advantages are low test cost per board, powerful digital and functional test capabilities, fast and thorough short and open testing, programmable firmware, high defect coverage, and ease of programming. The main disadvantages are the need for a test fixture, programming and debugging time, high fixture manufacturing costs, and difficulty in use.
4. Functional system testing
Functional testing is the earliest automatic testing principle. It is a comprehensive test of the functional modules of the circuit board using special testing equipment in the middle stage and end of the production line to confirm the quality of the circuit board. Functional system testing is based on a specific board or a specific unit and can be done using a variety of equipment. There is final product testing, latest physical models and stack testing. Functional testing typically does not provide in-depth data to improve processes, but instead requires special equipment and specially designed test procedures. Because writing functional test programs is very complex, it is not suitable for most circuit board production lines.
5.Laser detection system
Laser inspection uses a laser beam to scan the printed board, collect all measurement data, and compare the actual measurement value with the preset qualification limit value. This is the latest development in PCB testing technology, which has been proven on bare boards and is being considered for assembly board testing. The main advantages are fast output, no fixtures and unobstructed visual access; the disadvantages are high initial cost and maintenance and usage issues.
6. Automatic X-ray inspection
Automatic X-ray inspection is mainly used to detect defects in ultra-fine pitch and ultra-high-density circuit boards, as well as bridges, missing chips, poor alignment and other defects generated during the assembly process. The detection principle is to use the difference in X-ray absorption rates of different materials to inspect the parts to be tested and find defects. Tomography can also be used to detect internal defects in IC chips and is the only way to test 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 expense of fixtures.
7. Automatic optical inspection
Automated optical inspection, also known as automated visual inspection, is a relatively new method of identifying manufacturing defects. It is based on optical principles and comprehensively uses image analysis, computer and automatic control technology to detect and deal with defects encountered in production. AOI is often 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, generally more than ten times.