PCB testing has the status of "commander-in-chief" for PCB process quality. Which is also the core competition field of PCB manufacturers, which plays a fundamental role in the whole PCBA processing process. At present, the main PCB inspection technologies at home and abroad can be divided into two categories: visual inspection and electrical inspection, including PCB manual visual inspection, PCB on-line inspection (ICT), PCB function inspection (FCT), PCB active optical inspection (AOI) and PCB active X-ray inspection (AXL-Automatic X-ray inspection) and PCB laser detection, a total of 6 detection technologies.
1. PCB manual visual inspection
It mainly uses magnifying glass or microscope to manually identify short circuit, open circuit and some appearance defects on PCB, such as blistering, twisting, etc.
[advantages] cost economy
[disadvantage] poor error correction rate and great subjective deviation. With the narrowing of line width and line spacing, this method has been gradually eliminated
2. PCB online detection (ICT)
The principle of ICT detection is to simulate the electrical connection of PCB, so as to detect the main defects such as open circuit and short circuit of PCB through test points. ICT includes bed of nails tester and flying probe tester.
[advantages] low test cost, easy programming, high defect coverage rate
[disadvantage] special test fixture is required for PCB, which is relatively expensive and difficult to use
3. PCB function test (FCT)
Function testing is mainly to simulate the use of the product, connect and program PCB board through professional equipment, so as to truly reproduce the performance of the product in the use process.
[advantage] 100% ready to reproduce the performance of PCB
[disadvantage] the design process is complicated, high cost, and not suitable for most PCB fabrication processes
4. PCB active optical inspection (AOI)
At present, optical detection technology is generally mature, mainly based on optical principle, combined with computer and automatic control method, taking PCB graphics, comparing with preset images and programs, so as to detect PCB circuit connection problems accurately.
[advantage] the success rate of detection is very high
[disadvantage] the cost advantage is not very prominent, and the efficiency is moderate. Generally, a large number of testing equipment is needed to cope with the mass production
5. PCB active X-ray detection
X-ray detection is mainly used in high-precision and difficult processes, such as BGA and pop process design. Its principle is through X-ray irradiation projection, similar to artificial X-ray photography, so as to detect the internal defects of PCB board, and has good detection ability for blind hole embedding and other processes.
[advantage] adaptability of high difficulty detection
[disadvantage] high cost, poor detection efficiency and high repair cost
6. PCB laser detection
The principle is to use laser beam to scan PCB, collect all measurement data, compare the data with the preset limit value of the system, and accurately feedback the deviation between PCB and design on the data level, so as to accurately find defects.
[advantage] suitable for mass production, high speed, independent of fixture
[disadvantage] high initial cost, maintenance and program setting need professionals
PCB detection technology changes with each passing day, mainly in efficiency, accuracy and cost to find a balance. There are many detection equipment in the market, which can be used in different occasions, and it is easy to detect basic short circuit and open circuit defects. However, any PCB detection technology is inseparable from human management.
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