As a key part of electronic information products, the quality of Printed Circuit Board Assembly (PCBA) determines the quality of the final product. The process of PCBA production is very complicated, including incoming material inspection, SMT process, DIP plug-in, PCBA inspection and other important processes. Among them, PCBA inspection is the most critical quality control link. Failure to conduct a professional and timely inspection can lead to failure problems and catastrophic consequences. Therefore, PCBA manufacturers must inspect PCBA in real time during production to eliminate surface defects.
What are the inspection methods of PCBA?
The current mainstream production process testing includes: Visual Inspection, SPI (laser triangulation), AOI, Xray, ICT, FVT, each with different performance and defect coverage.
A. Visual inspection
The inspector checks for defects by looking at the light or by reflecting it from a prism. In general, visual inspection costs less, but visual inspection depends on the efficiency of the inspector. And this way is only suitable for more obvious defects, for small defects easy to produce fatigue and omission.
B. Solder Paste Inspection (SPI)
Solder Paste Inspection (SPI) is to check the height, volume, area, short circuit and offset of Solder Paste after printing, which can be said to be the front of AOI in a sense. At present, the main inspection methods in SPI field are laser inspection and fringe light inspection. The laser method is realized by point laser, but the laser detection is limited by the speed. At present, the mainstream technology is the use of moorings grating, combined with advanced phase profile modulation measurement technology (PMP) and triangulation method for all-round detection of solder paste.
C. Automated Optical Inspection (AOI)
With the densification and refinement of SMT packaging technology, the requirements for detection are increasing. AOI uses professional light source scanning, combines with high-resolution industrial cameras to pick up errors, and conducts professional analysis on the image and intensity of reflected light to determine product defects.AOI can be widely used to detect various visual defects, such as missing parts, position deviation, welding joint integrity, short circuit, cracks and other defects. In particular, AOI testing can make the product defects exposed before the electrical test, and make efficient use of the process control (SPC) data accumulation, so as to minimize the production cost and improve the product quality at the initial stage.
X-rays can see through the PCBA and check for defects in welded joints, such as cracks. In addition, it can check for missing components. It is suitable for BGA spot detection. However, with a two-sided PCBA, the X-ray system cannot accurately detect defects caused by overlapping images. Currently, many manufacturers have introduced X-ray lamination systems that can measure physical parameters on different planes. However, the cost and the coverage of defect detection are its weak point, especially the low detection speed is the bottleneck problem.
E.In – Circuit – Test/Manufacturing Defect Analyzer ICT/MDA
Both are standard means of testing the electrical connections of online components to see if the product is up to standard. It can check the missing parts, tombstones, wrong parts, bridge, polarity inversion, also can roughly detect the active parts (IC, BGA, QFN) of the welding problem, but for empty welding, false welding, cold welding problem is not good, because this kind of welding problem is intermittent.
F.Function Verification Test FVT/FCT
The traditional functional test method is usually combined with ICT or MDA. It is a full-function test when the simulation circuit board is actually installed into the whole machine. The defective PCBA is detected before the whole machine is assembled, so as to avoid finding the defects after the whole machine is assembled, thus affecting the quality and cost.
PCBA inspection has different requirements at different stages, and manufacturers should take into consideration the need to detect product defect types, cost and inspection speed in order to configure appropriate equipment.
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