How to conduct PCB quality inspection
In order to ensure the production quality of PCB boards, the manufacturer has passed a variety of detection methods in the production process. Each detection method will be specific to the defects of different PCB boards. Here KingFung technology tells you that PCB detection can be divided into electrical test and visual test
Broad categories.
1. Electrical test usually adopts the method of measuring the impedance characteristics between each test point by the wheatbridge to detect all conductivity (that is, open circuit and short circuit). The electrical test is more accurate in finding fault in short circuit or break.
2. the visual test mainly by visual inspection of the characteristics of electronic components and printed circuit characteristic points out the defects of the existing, can help you more easily detected incorrect gaps between the conductor, and visual inspection in the early stages of the production process in general, can let everybody as far as possible in the early stage of the production stage, find out the defects and repair to ensure the highest product percent of pass
PCBQUICK sorted out the following detection methods:
A. manual visual inspection: use magnifying glass or calibrated microscope, use operator's visual inspection to determine the circuit board disqualification, and determine when corrective operation is needed. It is the most traditional detection method. Its main advantages are low upfront cost and no test fixture, while its main disadvantages are human subjective error, high long-term cost, discontinuous defect detection, difficulty in data collection, etc. At present, as the output of PCB increases, wire spacing on PCB and component volume decrease, this method becomes less and less feasible.
B. Online testing: the manufacturing defects and the components of the analog, digital and mixed signals are found through the detection of electrical performance to ensure that they conform to the specifications. There are several testing methods such as needle bed tester and flying needle tester. The core advantages are low testing cost for each board, strong digital and functional testing ability, fast and thorough short circuit and open circuit testing, programming firmware, high defect coverage and easy programming. The disadvantage is that it requires testing fixtures, programming and debugging time, high cost of making fixtures, and difficulty in using.
C. Functional test: functional system test refers to the comprehensive test of the functional module of the circuit board by using special testing equipment at the intermediate stage and end of the production line 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 a specific board or a specific unit, and can be done by various devices. There are final product testing, the latest physical model and stacked testing types. 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 test procedures, so it is not suitable for most circuit board production lines.
D. Automatic optical detection, also known as automatic visual detection, is a relatively new method to identify manufacturing defects, which is based on the optical principle and USES various technologies such as image analysis, computer and automatic control comprehensively to detect and process the defects encountered in production. AOI is usually used before and after reflux and before electrical testing to improve the pass rate in the electrical treatment or functional testing stage. At this time, the cost of correcting defects is far lower than the cost after final testing, which is often up to a dozen times. E. Automatic X-ray inspection. Use different materials to different X-ray absorption rates. It is mainly used to detect the defects such as bridge, missing piece and poor alignment in the process of ultra-fine spacing and ultra-high density circuit board as well as assembly process. Besides, it can also detect the internal defects of IC chip with its tomographic imaging technology. It is now the only way to test the welding quality of the spherical grid array and the shielded tin balls. The main advantages are the ability to detect BGA welding quality, embedded components, no jig cost; The main disadvantages are slow speed, high failure rate, difficulty in detecting rework solder joints, high cost, and long program development time
F. Laser detection system, which is the latest development of PCB testing technology. It USES a laser beam to scan the printing plate, collect all the measurement data, and compare the actual measured value with the preset qualified limit value. This technique has been proven on the flat panel and is being considered for assembly board testing, with enough speed for mass production. Quick output, no need for clamping and visual non-covered access are its main advantages; High initial cost, maintenance and usage problems are mostly its main disadvantages.
G, dimension testing, secondary image measuring instrument, hole location, length, width, location and other dimensions. As PCB is a kind of small, thin and soft product, the contact measurement is easy to produce deformation, which leads to the inaccuracy of measurement. Therefore, the secondary image measurement instrument has become the best high-precision measurement instrument. After being programmed, the image-measuring instrument can realize automatic measurement, which not only has high precision, but also greatly shortens the measurement time and improves the measurement efficiency.
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