What are the common methods of image measuring instrument to detect PCB board?

by:Sinowon     2021-05-03

What are the common methods used by image measuring instruments to detect PCB boards?

1. Manual visual inspection of the PCB board Using a magnifying glass or a calibrated microscope, the operator’s visual inspection is used to determine the fault of the circuit board and determine when correction operations are needed. This is a more traditional inspection method, and its main advantages are lower upfront cost and no need for test fixtures. Its main disadvantages are human subjective error, high long-term cost, discontinuous defect detection and difficulty in data collection. At present, due to the increase of PCB output and the reduction of lead spacing and component volume on PCB, this method is becoming increasingly impossible. Row. 2. PCB board online testing Check electrical performance to find manufacturing defects and test analog, digital and mixed signal components to ensure they meet specifications. There are several test methods, such as bed of needle tester and flying probe tester. The main advantages are low test cost per board, powerful digital and functional test functions, fast and thorough short-circuit and open-circuit tests, programmed firmware, and high defect coverage The main disadvantages are the need to test fixtures, programming and debugging time, the high cost of fixture manufacturing and the difficulty of using them. 3. PCB board function test The function system test is to use special testing equipment to conduct a comprehensive test on the circuit board function modules in the middle of the production line and at the end of the production line to confirm the quality of the circuit board. Functional testing can be said to be an earlier principle of automatic testing. It is based on a specific board or a specific unit, and can be completed using various equipment. There are several types of final product tests, newer physical models and stacking tests. Functional tests usually do not provide in-depth data (such as pin position and Component-level diagnosis) to improve the process, but requires special equipment and a specially designed test process. Writing functional test programs is very complicated, so it is not suitable for most circuit board production lines. 4. Automatic optical inspection is also called automatic visual inspection. It is an updated method based on optical principles to confirm manufacturing defects. It combines image analysis, computer and automatic control technology to detect and deal with defects encountered in production. AOI usually Use 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 of final testing, usually more than ten times. 5. Automatic X-ray inspection of the X-ray absorption rate of different substances. It is necessary to check the parts to be inspected and find defects. It is mainly used to detect such as ultra-fine pitch and ultra-high-density circuit boards, as well as bridging, chip loss and failure during assembly. Defects such as alignment. It can also use its tomography technology to detect internal defects in IC chips. This is the only method currently used to test the soldering quality of ball grid arrays and shadow solder balls. The main advantage is the ability to check the quality of BGA soldering, embedded components , And there is no fixed cost; the main disadvantages are slow speed, high failure rate, difficulty in rework solder joint inspection, high cost and long program development time. It is a relatively new inspection, and the method needs to be further studied. 6. Laser inspection system image measuring instrument This is a relatively new development of PCB testing technology. It uses a laser beam to scan the printed board, collects all measurement data, and compares the actual measurement value with the preset pass limit value. This technology has It has been verified on the light board, and it is considering testing the assembly board at a speed sufficient for large-scale production lines. Its main advantages are fast output speed, no fixtures and barrier-free visual channels; its main disadvantages are High initial cost and many maintenance and usage issues.

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