In order to ensure the quality of PCB production, manufacturers have adopted a variety of testing methods. For example, visual Inspection, online Testing (ICT,In Ciruit Testing), AOI, AXI, Automatic X-ray Inspection, laser Inspection, etc. Each test method will be specific to different PCB defects to ensure the highest product pass rate. This paper introduces the current mainstream testing technology for SMT briefly.
1. Manual visual inspection
Use a magnifying glass or microscope and a visual inspection by the operator to determine if the board is up to standard. Its main advantages are labor-intensive, but its main disadvantages are the subjective error of people, easy fatigue, high labor costs. At present, as PCB production increases and component volume shrinks, this method becomes increasingly unfeasible.
2. Ciruit Testing (ICT)
ICT detect manufacturing defects by testing electrical properties, including Bed of Nails Tester and Flying Probe Tester. The primary advantages of ICT are rapid testing of short and open circuits, high defect coverage, and ease of programming. The main disadvantages are the need to test fixture, long debugging time, high cost problems.
3. Automatic optical inspection (AOI) for SMT inspection technology
Also known as automatic visual inspection, it bases on the optical principle, comprehensive use of hd industrial camera image acquisition, software analysis and other technologies, the production of defects encountered in the detection and processing, is a relatively new method to confirm the manufacturing defects. Product line usually use AOI before and after reflux and before electrical testing, where the cost of correcting defects is the lowest and the efficiency is the highest.
4. Automatic X-ray Inspection (AXI) for SMT inspection technology
AXI perspective the parts to test and find the defects. It is mainly used to detect internal defects of IC chips and BGA welding quality (Ball Grid Array). The main advantage of AXI is the ability to detect embedded components without fixture cost. But, the main disadvantages are slow speed, high failure rate, high cost, programming slowly.
5. Laser detection system
It is the latest development of PCB testing technology. It USES a laser beam to scan the PCB, and collects all data from sensor. Then, it compares the actual measured value with the preset qualified limit value. Now, this technique has been demonstrated on optical plates, and is being considered for assembly plate testing. The main advantages are fast output, do not require fixture; The main disadvantages are high initial cost and many maintenance and use problems.
Comments on inspection methods for PCB testing
Manual testing is phasing out. In contrast, electrical testing is more accurate when looking for a short circuit or open circuit faults. Visual test can be more easily detected problems in the early stages of production process. Thus, visual test can ensure the highest product percent of pass. AOI is a visual test detection mean. AOI’s detection efficiency is much higher, and reliability is much more stable. AXI can find the defects inner or coverd by commponents. Laser detection system has hgh test speed.