[Repost] Effective countermeasures for PCB process film deformation[Copy link]
In the PCB copying process, the failure of temperature and humidity control or the excessive temperature rise of the exposure machine sometimes causes the film to deform. If it is not improved, it will affect the quality and performance of the final PCB copy, but directly abandoning it will cause cost losses. Then mastering the correction process of film deformation will make the work better. The editor summarizes five simple and commonly used methods for everyone to use when needed. The following is for reference only. The specific measures depend on the situation. 1. Splicing method For graphics with simple circuits, large line width and spacing, and irregular deformation, cut the deformed part of the film, compare the hole position of the drilling test board, and then copy it. Of course, this is for graphics with simple deformation circuits, large line width and spacing, and irregular deformation; it is not applicable to films with high wire density and line width and spacing less than 0.2mm. When splicing, pay attention to minimizing the damage to the wires and the pads. When revising the version after splicing and copying, pay attention to the correctness of the connection relationship. This method is suitable for the correction of films with less dense circuits and inconsistent deformation of each layer of film, solder mask film and multi-layer board power supply layer film, and the effect is particularly obvious. 2. PCB copy board change hole position method Under the condition of mastering the operation technology of the digital programmer, first compare the film and the drilling test board, measure and record the length and width of the drilling test board respectively, and then adjust the hole position on the digital programmer according to the size of the two deformations of its length and width, and use the adjusted drilling test board to cater to the deformed film. The advantage of this method is that it eliminates the tedious work of cutting and splicing films and can ensure the integrity and accuracy of the graphics. The disadvantage is that it is not effective for the correction of films with very serious local deformation and uneven deformation. To use this method, you must first master the operation of the digital programmer. After using the programmer to lengthen or shorten the hole position, the hole position that exceeds the tolerance should be reset to ensure accuracy. This method is suitable for the correction of films with dense circuits or films with consistent deformation of each layer. Third, the pad overlap method enlarges the hole on the test board into a pad to overlap the deformed circuit piece to ensure the minimum ring width technical requirements. Because after overlapping copying, the pad is elliptical, and after overlapping copying, the halo and deformation of the line and disk edge. If the user has very strict requirements on the appearance of the PCB board, please use it with caution. This method is suitable for negatives with line width and spacing greater than 0.30mm and not too dense graphic circuits. Fourth, the photographic method only needs to use a camera to enlarge or reduce the deformed graphics. Usually the film loss is large, and it takes multiple debugging to obtain a satisfactory circuit graphic. When taking pictures, the focus must be accurate to prevent line deformation. This method is only applicable to silver salt negatives. It can be used when it is inconvenient to re-drill the test board and the deformation ratio of the length and width of the film is consistent. Five. Hanging method: In view of the physical phenomenon that the film changes with the change of environmental temperature and humidity, take it out of the sealed bag before copying the film, and hang it in the working environment for 4-8 hours, so that the film has deformed before copying, then the probability of deformation after copying is very small. For the deformed film, other methods need to be adopted. Because the film will change with the change of environmental temperature and humidity, when hanging the film, it is necessary to ensure that the humidity and temperature of the hanging place are consistent with the working place, and it is necessary to be in a ventilated and dark environment to prevent the film from being contaminated. This method is suitable for the film that has not been deformed, and it can also prevent the film from deforming after copying. Of course, the above are all remedial methods after the film is deformed. Engineers should still consciously prevent the deformation of the film. In the PCB copying process, the temperature is usually strictly controlled at 22±2℃, the humidity is at 55%±5%RH, a cold light source or an exposure machine with a cooling device is used, and the backup film is constantly replaced.
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