PCB Tech - How to check the welding quality of circuit boards

How to check the welding quality of circuit boards
1. The visual method of PCB
The visual method of the circuit board relies on the human eye to directly observe the soldering condition of the solder joint surface, which can detect poor wettability, inappropriate solder volume, pad falling off, bridging, small solder ball splashing, solder joint dullness and leakage. Welding defects such as welding. The easiest tool for visual inspection is a magnifying glass, generally a fixed magnifying glass with a light of 5 to 10 times is used. It is completely suitable for the inspection of low-density circuit board welding. The disadvantage of this tool is that inspectors are prone to fatigue, and a better visual inspection instrument is a camera-type screen display inspection instrument, whose magnification is adjustable, up to 80 to 90 times. It displays the welding parts of the circuit 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 locate it to realize the inspection of the key parts of the PCBA. Equipped with a video recorder, the inspection results can be recorded.
2. Infrared detection method
The infrared detection method of the circuit board uses the infrared beam to radiate heat to the solder joint of the circuit board, and then detects whether the heat release curve of the solder joint is normal, so as to determine whether there is a cavity inside the solder joint, and achieve the purpose of indirect inspection of the welding quality. This inspection method is suitable for large-volume, automatic welding, and the consistency of the pads is good, and the volume of the components is not much different. 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, there are fewer applications in electronic product testing.

3. X-ray fluoroscopy
The X-ray fluoroscopy method of the circuit board uses the characteristic that the ability of X-ray 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 the soldering 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.
4. Online testing method
The on-line test method is realized by an on-line tester, which connects the test point 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 circuit board has a high component density 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. iPCB is happy to be your business partner. Our business goal is to become the most professional prototyping PCB manufacturer in the world. With more than ten years of experience in this field, we are committed to meeting the needs of customers from different industries in terms of quality, delivery, cost-effectiveness and any other demanding requirements. As one of the most experienced PCB manufacturers and SMT assemblers in China, we are proud to be your best business partner and good friend in all aspects of your PCB needs. We strive to make your research and development work easy and worry-free.