The problem of substrate size changes during PCB manufacturing[Copy link]
PCB is the abbreviation of Printed circuit board in English. To put it simply, it is a printed circuit board. It appears in almost every electronic device. If there are electronic parts in a certain device, they are all mounted on PCBs of different sizes. In addition to fixing various small parts, the main function of PCB is to provide electrical connections between the various parts on it.
The problem of substrate size change during PCB manufacturing process: Reason: ⑴ The difference in the longitude and latitude directions causes the substrate size to change; because the fiber direction is not paid attention to during shearing, the shear stress remains in the substrate. Once released, it directly affects the shrinkage of the substrate size. ⑵ The copper foil on the surface of the substrate is etched away, which limits the change of the substrate. When the stress is eliminated, the size changes. ⑶ When brushing the board, due to excessive pressure, compressive and tensile stresses are generated, causing the substrate to deform. ⑷ The resin in the substrate is not completely cured, resulting in dimensional changes. ⑸ Especially before lamination of multilayer boards, the storage conditions are poor, causing thin substrates or prepregs to absorb moisture, resulting in poor dimensional stability. ⑹ When the multilayer board is pressed, excessive glue flow causes the deformation of the glass cloth. Solution: ⑴ Determine the change law of the warp and weft directions and compensate on the film according to the shrinkage rate (do this work before light drawing). At the same time, process according to the fiber direction when cutting, or process according to the character mark provided by the manufacturer on the substrate (generally, the vertical direction of the character is the longitudinal direction of the substrate). ⑵ When designing the circuit, the entire board surface should be distributed evenly as much as possible. If it is not possible, a transition section must be left in the space (mainly without affecting the circuit position). This is due to the difference in the density of the warp and weft yarns in the glass cloth structure of the board, which leads to the difference in the warp and weft strength of the board. ⑶ Test brushing should be used to make the process parameters in the best state, and then the board is hardened. For thin substrates, chemical cleaning process or electrolytic process method should be used for cleaning. ⑷ Take baking method to solve it. In particular, baking should be carried out before drilling, with a temperature of 120℃ for 4 hours to ensure the curing of the resin and reduce the deformation of the substrate size due to the influence of cold and heat. ⑸ The substrate with oxidation treatment in the inner layer must be baked to remove moisture. And store the processed substrate in a vacuum drying oven to prevent it from absorbing moisture again. (6) It is necessary to conduct a process pressure test, adjust the process parameters and then press. At the same time, the appropriate amount of glue flow can be selected according to the characteristics of the prepreg.
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