We can use the following four methods when inspecting the PCB welding section.
1.PCB triangulation (optical cutting, photostructuring)
The triangulation method is usually used to check the three-dimensional shape.The triangulation method has been developed to detect the cross section shape of the solder lead.However, since triangulation is observed from different directions of light incidence, this method is most suitable when the object surface is light diffuseness.When the solder surface is close to the mirror surface, this method is not suitable.
2. Measurement of light reflection distribution
The optical reflection distribution measurement method is the typical inspection method of the welding department inspection device in the market.At this time, in order to know the Angle of solder surface, it is necessary to know the Angle information of the irradiated light, point out the lamps of various angles, and obtain the Angle information according to the color of each lamp.Instead, shine a light beam from above, measure the Angle distribution of light reflected by the solder surface, and check the inclination of the solder surface.
The optical reflectance distribution measurement of the device can easily detect the Angle of the solder surface, and the device is inexpensive.Its disadvantages are :(1) due to the need to use large Angle lighting, the shadow effect of components is produced along with the high density, and even the detection is difficult sometimes;(2) although the Angle of the solder surface is known, the absolute height cannot be known. If the integral is, the height can be calculated, but it may be unstable.(3) the ratio of 45 cannot be detected.Steeper surface.
3. Check the image by changing the Angle of multiple cameras
The inspection device has multiple (5) cameras with different angles and lighting composed of multiple leds.The reliability can be improved by using multiple images and near visual conditions.
4. Focus detection method
The methods in section 1 to 3 are detection methods that require wide solid angles.For a high density mounting substrate, not the desired condition.For example, the multi-focus method, which can directly detect the height of the solder surface, is a high-precision detection method.The position of the solder surface is found by calculating the focal plane obtained by the maximum output.The object was irradiated with a fine laser beam, and 0 focal position detectors with pinhole were staggered in the z direction.Installation of 3mm pitch leads.