Function analysis of various SMT appearance inspection equipment AOI

a) : Used to measure the solder paste printing quality inspection machine SPI after the printing machine: SPI inspection is carried out after the solder paste printing, and defects in the printing process can be found, thereby reducing the soldering defects caused by poor solder paste printing to a minimum. Typical printing defects include the following points: insufficient or excessive solder on the pads; printing offset; tin bridges between the pads; thickness and volume of the printed solder paste. At this stage, there must be powerful process monitoring data (SPC), such as printing offset and solder volume information, and qualitative information about printed solder will also be generated for analysis and use by production process personnel. In this way, the process is improved, the process is improved, and the cost is reduced. This type of equipment is currently divided into 2D and 3D types. 2D cannot measure the thickness of solder paste, only the shape of solder paste. 3D can measure both the thickness of the solder paste and the area of the solder paste, so that the volume of the solder paste can be calculated. With the miniaturization of components, the thickness of the solder paste required for components such as 01005 is only 75um, while the thickness of other common large components is about 130um. An automatic printer that can print different solder paste thicknesses has emerged. Therefore, only 3D SPI can meet the needs of future solder paste process control. So what kind of SPI can we really meet the needs of the process in the future? Mainly these requirements:

1. It must be 3D.
2. High-speed inspection, the current laser SPI thickness measurement is accurate, but the speed can not fully meet the needs of production.
3. Correct or adjustable magnification (optical and digital magnification are very important parameters, these parameters can determine the final detection capability of the device. To accurately detect 0201 and 01005 devices, optical and digital magnification is very important, and it is necessary to ensure that the detection algorithm provided to the AOI software has sufficient resolution and image information). However, when the camera pixel is fixed, the magnification is inversely proportional to the FOV, and the size of the FOV will affect the speed of the machine. On the same board, large and small components exist at the same time, so it is important to select the appropriate optical resolution or adjustable optical resolution according to the size of the components on the product.
4. Optional light source: the use of programmable light sources will be an important means to ensure the maximum defect detection rate.
5. Higher accuracy and repeatability: The miniaturization of components makes the accuracy and repeatability of the equipment used in the production process more important.
6. Ultra-low misjudgment rate: Only by controlling the basic misjudgment rate can the availability, selectivity and operability of the information brought by the machine to the process be truly utilized.
7. SPC process analysis and defect information sharing with AOI in other locations: powerful SPC process analysis, the ultimate goal of appearance inspection is to improve the process, rationalize the process, achieve the optimal state, and control manufacturing costs.

b) . AOI in front of the furnace: Due to the miniaturization of components, it is difficult to repair 0201 component defects after soldering, and the defects of 01005 components cannot be repaired basically. Therefore, the AOI in front of the furnace will become more and more important. The AOI in front of the furnace can detect the defects of the placement process such as misalignment, wrong parts, missing parts, multiple parts, and reverse polarity. Therefore, the AOI in front of the furnace must be online, and the most important indicators are high speed, high accuracy and repeatability, and low misjudgment. At the same time, it can also share data information with the feeding system, only detect the wrong parts of the refueling components during the refueling period, reducing system misreports, and also transmit the deviation information of the components to the SMT programming system to modify the SMT machine program immediately .

c) AOI after the furnace: AOI after the furnace is divided into two forms: online and offline according to the boarding method. The AOI after the furnace is the final gatekeeper of the product, so it is currently the most widely used AOI. It needs to detect PCB defects, component defects and all process defects in the entire production line. Only the three-color high-brightness dome LED light source can fully display different solder wetting surfaces to better detect soldering defects. Therefore, in the future, only the AOI of this light source has room for development. Of course, in the future, in order to deal with different PCBs The order of colors and three-color RGB is also programmable. It’s more flexible. So what kind of AOI after the furnace can meet the needs of our SMT production development in the future? That is:

1. high speed.
2. High precision and high repeatability.
3. High-resolution cameras or variable-resolution cameras: meet the requirements of speed and precision at the same time.
4. Low misjudgment and missed judgment: This needs to be improved on the software, and the detection of welding characteristics is most likely to cause misjudgment and missed judgment.
5. AXI after the furnace: Defects that can be inspected include: solder joints, bridges, tombstones, insufficient solder, pores, missing components, IC lifted feet, IC less tin, etc. In particular, X-RAY can also inspect hidden solder joints such as BGA, PLCC, CSP, etc. It is a good supplement to visible light AOI.