The appearance inspection of a printed circuit board can also be referred to as visual inspection, and the purpose is to visually check whether the quality of the circuit board conforms to the manufacturing standard.
The soldering inspection of the board first depends on the soldering condition of the solder and the geometry of the solder joints, and then the visual inspection is performed mainly on the brightness and gloss of the pcb solder joints.
The wetting of the solder is generally judged by a method of forming a contact angle formed by solid metal surface and molten solder. The geometry of the joint is also an important evaluation object. According to the shape of the joint portion, it can be judged whether the pcb solder joint can meet the requirements of electrical characteristics and mechanical strength. In addition, it is necessary to judge whether the amount of solder is appropriate or not. According to the above situation, the appearance of a typical pcb solder joint is summarized.
1) The shape is centered on the welding wire, and it is symmetrical and skirted.
2) The joint surface of the brazing material has a semi-bow concave surface, the joint between the brazing material and the weldment is smooth, and the contact angle is as small as possible.
3) The amount of solder is moderate and the surface is shiny and smooth.
4) No welding defects such as cracks, pinholes, slag inclusions, tipping, and floating soldering. In short, the quality of the good pcb solder joints should be: the solder joints are bright and smooth; the solder layer is even and thin, and the ratio of the pad size is appropriate, the contour of the joint is faintly visible; the solder is sufficient, and the skirt is scattered; Cracks, pinholes and flux residues. All obvious defects found in the appearance inspection should be dealt with in time to avoid more outflows of defective products.