Application of machine vision inspection technology in preventing PCB board manufacturing defects

In the world of modern electronic products, PCB (printed circuit board) is an important part of the composition of electronic products. It is difficult to imagine that there is no PCB in an electronic device, so how the quality of PCB will affect the long-term normal reliability of electronic products Work has a very big impact. Improving the quality of PCBs is an important issue that electronics manufacturers should pay enough attention to.

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The implementation of an excellent solder paste printing process can cause problems in the connection of electronic circuits. In order to effectively solve this problem, many screen printing equipment manufacturers have adopted online machine vision inspection technology. The following is a brief introduction by Jingke Zhizao.

Industrial camera positioning and inspection

In general conventional on-line visual inspection applications, an industrial camera is placed above the circuit board to acquire images of the printing position, and can send the relevant images to the processing system of the visual inspection equipment. There, the image analysis software will compare the acquired image with a reference image stored in the same location in the device memory. In this way, the system can confirm whether more or less solder paste is applied. Similarly, the system can also reveal whether the position of the solder paste on the pads is aligned. It can find out if there is excess solder paste between the two pads to form a bridge-like connection phenomenon? This problem is also known as the "bridge" phenomenon of many printed circuit board manufacturers.

The inspection of the stencil gap is in the same form. When excess solder paste is accumulated on the surface of the printing stencil, the vision system can be used to detect whether the gap is blocked by the solder paste, or whether tailing has occurred. After a defect is found, the device can immediately automatically request a series of cleaning operations on the screen below, or warn the operator that there is a problem and needs to be repaired. Inspection of printed templates can also provide users with very useful data on print quality and consistency.

A key function of the online vision system is the ability to inspect highly reflective PCB circuit boards and pad surfaces, as well as inspect under uneven light conditions or under conditions where dry solder paste structures cause differences. For example, HASL circuit boards typically exhibit uneven, flat surfaces, variable surface contours, and reflective features. To obtain higher quality images, proper lighting also plays a very important role. The light must be able to "aim" the fiducials and pads of the board, which in turn transforms other invisible features into clearly identifiable shapes. In this way, vision software algorithms can be used in the next step to fully realize their potential capabilities.

In some specific occasions, the vision system can be used to detect the height or volume of the solder paste on the pads, and sometimes only offline inspection systems may be used to do these things. Adopting this procedure means forming a corresponding stacking degree in a given printing template to confirm whether the volume of solder paste is missing on the same pad.

In actual inspection, it can be divided into two categories: the detection of solder paste on PCB and the detection of solder paste on printed templates:

a. PCB inspection

Mainly detect printing area, printing offset and bridging phenomenon. Inspection of the printed area refers to the area of solder paste above each pad. Excessive solder paste may cause bridging phenomenon, and too small solder paste may cause the phenomenon of weak solder joints. The detection of the printing offset is whether the amount of solder paste on the pad is different from the specified position. The detection of the bridging phenomenon is aimed at whether the amount of solder paste applied between two adjacent pads exceeds a prescribed amount. These excess solder paste can cause electrical shorts.

b. Inspection of printed templates

The detection of printed templates is mainly for blocking and smearing. Blockage detection is the detection of solder paste deposits in the holes on the printed stencil. If the holes are blocked, then too little solder paste may be applied at the next printing point. The detection of smearing refers to whether excessive solder paste has accumulated on the surface of the printing stencil. These excess solder pastes may be applied to locations on the circuit board that should not be conductive, causing electrical connection problems.

Online machine vision systems can benefit PCB manufacturers in different ways. In addition to ensuring the high integrity of the solder joints, it can prevent manufacturers from wasting costs due to circuit board defects and rework. Perhaps it is important that it can provide continuous process feedback, which can not only help manufacturers optimize the screen printing process, but also increase people's confidence during the process operation.