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Circuit boards, circuit boards, PCB boards, PCB soldering technology in recent years, the development of electronic industry technology, you can notice a very obvious trend is reflow soldering technology. In principle, traditional plug-in parts can also be reflow soldered, which is commonly referred to as through-hole reflow soldering. The advantage is that it is possible to complete all solder joints at the same time, minimizing production costs. However, temperature-sensitive components have limited the application of reflow soldering, whether it is plug-in parts or SMD. Then people turn their attention to soldering. In most applications, selective soldering can be used after reflow soldering.
The following is an introduction to the quality inspection of PCB circuit board welding
At present, the inspection methods for PCB soldering quality include visual method, infrared detection method, online testing method, etc. Among these methods, the most economical and most commonly used is the visual method, which is economical, convenient, simple and feasible. Several other methods require certain equipment support. Although they have a large investment, they can guarantee high inspection reliability.
★Visual method
The visual method relies on the human eye to directly observe the soldering condition of the solder joint surface, which can check the poor wettability, inappropriate solder volume, pad falling off, bridging, small solder ball splashing, dull solder joints, and missing soldering.
defect. The easiest tool for visual inspection is a magnifying glass. Generally, a fixed magnifying glass with 5 to 10 times light is used. It is completely suitable for the inspection of soldering of low-density circuit boards. The disadvantage of this tool is that inspectors are prone to fatigue, and a better visual inspection instrument is a camera-type screen display inspector whose magnification can be adjusted up to 80 to 90 times. It displays the welding part of the board on the screen through CCD, and people can observe the screen like watching TV. The higher-grade inspection instrument can automatically move the circuit board welding in two directions, and can also automatically position it to realize the inspection of the key parts of the PCBA. Equipped with a video recorder, the inspection results can be recorded.
★Infrared detection method
The infrared detection method uses infrared beams to radiate heat to the solder joints of the circuit board, and then detects whether the heat release curve of the solder joints is normal, so as to determine whether there are voids inside the solder joints and achieve the purpose of indirect inspection of the welding quality. This inspection method is suitable for large-volume, automatic welding, with good pad consistency and little difference in component volume. Otherwise, other factors have too much influence on the heat dissipation characteristics of the solder joints. The false detection rate will increase. Because this detection method is subject to many restrictions, after all, the size of the solder joints for any kind of circuit board welding will be different. Therefore, it is less used in electronic product testing-Shanghai PCB Welding Friendship pointed out!
★X-ray perspective
X-ray fluoroscopy uses the characteristic that the ability of X-rays to pass through the solder is not strong enough to pass through materials such as copper, silicon, FR-4, etc., to show the density distribution of solder thickness, shape, and quality. This detection method is suitable for invisible solder joints (ie, recessive soldering). It welds the circuit board to be tested in the X-ray channel, and it can be seen on the display that the solder joint solder obstructs the X-ray passing through the solder joint contour formed.
★Online test method
The online test method is implemented with an online tester, which connects the test points welded on the circuit board with the tester through a signal connection component called the "bed of needles" on the tester. You can check the open circuit, short circuit and faulty components of the circuit board welding, and also check the function of the component, such as the value of the resistance and the capacitance, the polarity of the transistor, etc. The IC's dummy solder pins can be checked by the IC floating pin test method. If the component density of the circuit board is high and it is difficult to set the required test points, you can use boundary scan technology to gather those test points through the designed test circuit to the edge connector of the circuit board soldering, so that the online tester can measure Points required in various locations.
The online test method is an electrical signal test method. It can check the welding status of PCB welding. This inspection is very close to the practical situation. Generally, the circuit board welding that has been tested online can be installed on the machine, but it cannot give the quality results of the welding and the welding point is not intuitively reliable. Sex check.
