SMT solder joint quality and solder joint defects
For circuit products formed by SMT, the quality of the solder connection points is the main indicator of product quality. The quality of solder joints can generally be judged by whether the solder joints are defective. Solder joint defects are the main manifestation of SMT product assembly failures. Whether it is a welding failure caused by the welding process, or a quality hazard caused by other process links such as solder paste printing and patching, or even quality problems caused by raw materials, most It can be reflected from the solder joint defects that are finally formed.
Due to many factors affecting the quality of solder joints, the manifestations of solder joint defects are also ever-changing. Typical solder joint defects include bridging (adjacent solder joints overlap), lack of tin (the solder joint is not full), tin picking (the solder joint tends to shrink to a single object to be welded), and virtual welding (the solder joint is separated from the object to be welded) Phenomenon), solder beads (small solder balls splashed near the solder joints), red eyes (the red copper pads are visible when no solder is attached to the soldering area of the substrate), voids (bubbles in the middle of the solder joints), etc. According to the visual and invisible distinction of solder joint defects, most of the solder joint defects are visible from the appearance of the solder joints.
For visible solder joint defects, through manual visual inspection and analysis with the help of optical inspection equipment or computer-aided automatic detection and analysis, solder joint quality evaluation information or conclusions can be drawn. The method of analysis and evaluation is generally to compare the features or design rules of defective solder joints and ideal solder joints, and then analyze and evaluate the differences between the two and their causes. Even the BGA (Ball Grid Array) type invisible solder joints distributed on the bottom plane of the device can automatically obtain the actual solder joint morphology for analysis and evaluation through techniques such as X-ray layered scanning. Therefore, in the inspection and control of SMT solder joint quality, the research and analysis of solder joint morphology is an important task.
