PCB News - What are the PCBA performance parameters

What are the PCBA performance parameters
The performance parameters of PCBA are closely related to the PCB manufacturing process and the design requirements of PCB designers. Among the many PCB parameters, the main influence on the placement process is its geometrical size parameters, including the flatness and flatness of the entire PCB. The impact of PCB manufacturing tolerances and PCB surface treatment, etc., is organized and introduced below for everyone.

1, flatness
According to the characteristics and manufacturing process of PCBA, we know that it is formed by bonding layer by layer, stress will be generated during the manufacturing process, and the material and thickness of the pad layer and the electrical isolation layer in the middle are different, so The coefficient of thermal expansion is also different. Therefore, during packaging and transportation, the PCB may undergo plastic deformation (Bow) or twist (Twist). The degree of plastic deformation is related to the thickness and area of the PCB and whether its layer design is symmetrical or not. .
The allowable value of PCB bending and twisting is 0.75% of the PCB length L, which is (L*0.75%) mm, but the maximum value cannot exceed 3.175 mm.

If the flatness exceeds the allowable range, the shape of the fiducial point in the camera will change. For example, the shape of the standard circle fiducial point in the camera will become an ellipse, which will cause the reading of the center distance between the fiducial points to change, which will affect The position of the component pad on the PCB relative to the reference point, which may directly cause the component to be biased. In addition, due to the warpage of the PCB during the placement process, the component will slide relative to the solder paste on the pad during the pressing process, or the solder paste at the bottom of the component will be squeezed away, thereby forming a solder ball or causing a short circuit between adjacent components. .

2, the influence of manufacturing tolerances

PCB manufacturing tolerances will also have an impact on the placement quality, which is mainly reflected in the fiducial profile and position deviations. As for other errors on the PCB, such as the manufacturing tolerances of the vias, it will directly affect the post-welding The electrical performance, but this does not belong to the impact on the placement machine.

3. Surface treatment
The impact of surface treatment on placement is mainly reflected in the coverage of fiducials. It can mainly affect whether the video system can accurately and quickly identify fiducials. The important principle is that the solder mask cannot cover the reference point and the auxiliary resolution area around it. The Internet era has broken the traditional marketing model, and a large number of resources have been gathered together to the greatest extent through the Internet, which has also accelerated the development speed of FPC flexible circuit boards, and then as the development speed accelerates, environmental problems will continue to appear inPCB factories. In front of you. However, with the development of the Internet, environmental protection and environmental informatization have also been developed by leaps and bounds. Environmental information data centers and green electronic procurement are gradually being applied to the actual production and operation fields.