When inspecting the soldering part of the PCB board, we can use the following four methods.
1. PCB triangulation Method (light cutting method, light structuring method)
The method of checking the three-dimensional shape is generally triangulation. A device has been developed for detecting the cross-sectional shape of the solder lead portion using a triangulation method. However, since the triangulation method observes from different directions of light incidence, this method is most suitable when the object surface is essentially light diffusive. This method is not suitable when the solder surface is close to the mirror surface condition.
2. Light Reflection Distribution Measurement Method
The light reflection distribution measurement method is a representative inspection method using a commercially available weld inspection device. Light is incident from an oblique direction, and a TV camera is installed above to detect it. At this time, in order to know the angle of the solder surface, it is necessary to know the angle information of the irradiated light, turn off lights at various angles, and obtain the angle information from the color of each lamp. Instead, irradiate the beam from above, measure the angular distribution of the light reflected by the solder surface, and check the inclination of the solder surface.
The light reflection distribution measurement method of this device can easily detect the angle of the solder surface, and the device is inexpensive. Its disadvantages are:
(1) Because of the need to use large-angle illumination, the shadow of the component is affected by the high density, and sometimes it is even difficult to detect.
(2) Although the angle of the solder surface is known, the absolute height cannot be known. If the integral , the height can be calculated, but may be unstable).
(3) Surfaces steeper than 45° cannot be detected.
3. Method of Inspecting Images Using Multiple Cameras of Varying Angles
The inspection device has multiple (five) cameras with varying angles and illumination composed of multiple LEDs. Often multiple images are used, and inspections under conditions close to visual inspection can improve reliability.
4. Focus Detection and Utilization Method
The methods in Sections 1 to 3 are all detection methods that require a wide solid angle. This is not a desirable condition for a high-density mounting board. For example, the multi-segment focus method can directly detect the height of the solder surface, which is a high-precision detection method. Ten focal plane detectors are installed, and the position of the solder surface is detected by finding the focal plane obtained by the maximum output. By irradiating the object with a fine laser beam, and staggering 10 focal position detectors with pinholes in the z direction, the installation of 0.3mm pitch leads can be successfully checked.
The above are some of the inspection methods for the welding part when we conduct an external inspection of the PCB board.
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