PCB Technical - How to deal with PCB board process negative film deformation

For the PCB copy board, a slight carelessness may cause the bottom plate to deform. If it is not improved, it will affect the quality and performance of the PCB copy board. If it is directly discarded, it will cause costs. On the loss. Here are
some ways to correct the deformation of the bottom plate.

1. Splicing method
For graphics with simple lines, large line widths and spacing, and irregular deformations, cut the deformed part of the negative film, resplice the holes according to the hole positions of the drill test board, and then copy them. Of course, this is for
deformed lines. Simple, large line width and spacing, and irregularly deformed graphics; it is not suitable for negatives with high wire density and line width and spacing less than 0.2mm. When splicing, you need to pay as little as possible to
damage the wires and not 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 film that is not too densely packed and the film deformation
of each layer is inconsistent. The effect is particularly obvious for the correction of the solder mask film and the film of the power supply layer of the multilayer board.

2. Printed Circuit Board copy board to change the hole position method
Under the condition of mastering the operating technology of the digital programming instrument, first compare the negative film and the drilling test board, measure and record the length and width of the drilling test board respectively, and
then use the digital programming instrument according to its length and width. The size of the deformation, adjust the hole position, and adjust the adjusted drilling test board to cater to the deformed negative. The advantage of this method is
that it eliminates the cumbersome work of editing negatives, and can ensure the integrity and quality of the graphics. The disadvantage is that the correction of the negative film with very serious local deformation and uneven deformation is not
effective. To use this method, you must first master the operation of the digital programming instrument. After the programming instrument is used to lengthen or shorten the hole position, the out-of-tolerance hole position should be reset to
ensure the performance. This method is suitable for correcting the negative film with dense lines or the uniform deformation of the negative film of each layer.

3. Pad overlap method
Enlarge the holes on the test board into pads to overlap and deform the circuit piece to ensure the technical requirements of the ring width. After overlapping copy, the pad is ellipse, after overlapping copy, the line and disk edge halo and deform.
If the user has very strict requirements on the appearance of the PCB board, please use it with caution. This method is suitable for film with line width and spacing greater than 0.30mm, and the pattern lines are not too dense.

4. Photography
Just use the camera to enlarge or reduce the deformed graphics. Normally, the film loss is relatively high, and it needs to be debugged many times to obtain a satisfactory circuit pattern. The focus should be accurate when taking pictures to
prevent the lines from being deformed. This method is only suitable for the silver salt film, and it can be used when it is inconvenient to drill the test board again and the deformation ratio in the length and width directions of the film is the same.

5. Hanging method
In view of the physical phenomenon that the negative film changes with the environmental temperature and humidity, take it out of the sealed bag before copying, and hang it for 4-8 hours under working environment conditions, so that the
negative film has been deformed before copying. After copying, the chance of deformation is very small. For the film that has been deformed, other measures need to be taken. Because the negative film will change with the change of
environmental temperature and humidity, when hanging the negative film, make sure that the humidity and temperature of the hanging place is consistent with the working place, and it needs to be in a ventilated and dark environment to
prevent the negative film from being contaminated. This method is suitable for the negative film that has not been deformed, and can also prevent the negative film from deforming after copying.