In the PCB copying process, there will be some special circumstances that make it difficult for people to make a difference. Some of them are improperly operated and cause the film to be deformed. This is a dilemma. It is to continue, affecting the quality and performance of the final PCB copy board, or directly discard it. No need to cause cost loss? There are actually ways to fix the deformed film. These methods include:
PCB copy board change hole position method
Pad overlap method
The method mentioned above is a very important method, so let's talk about these methods separately and hope to help everyone.
1. Splicing method:
This method is suitable for the correction of the film which is not dense in line, the deformation of the film of each layer is inconsistent, and the correction of the film of the solder mask and the power layer of the multilayer board. Specific operation: cut the deformed part of the film, re-splicing the hole position of the hole test plate, and then copying. Of course, this is for the simple deformation line, large line width and spacing, and irregular deformation. Graphics; not suitable for negatives with high wire density, line width and spacing less than 0.2 mm.
PS: Pay attention to minimize the damage to the wire when splicing, and do not damage the pad. Pay attention to the correctness of the connection relationship when splicing and copying.
2. PCB copy board change hole position method:
This method is suitable for corrections in which the lines are densely packed, or the deformation of the layers is uniform. Specific operation: first compare the negative film and the drilling test plate, measure and record the length and width of the drilling test plate separately, and then adjust the hole according to the length and width of the deformation on the digital programmer. Position, the adjusted drill test plate will be used to cater to the deformed film. The advantage of this method is that it eliminates the tedious work of splicing the negative film and ensures the integrity and accuracy of the graphic. The disadvantage is that the correction of the film which is very severe in local deformation and uneven deformation is not effective.
PS: 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, you should reset the hole position to ensure accuracy.
3. Pad overlap method:
This method is suitable for negative films with line widths and spacings greater than 0.30 mm and less dense graphics lines. Specific operation: enlarge the holes on the test board into pads to overlap the deformed circuit pieces to ensure the minimum loop width technical requirements.
PS: After overlapping copies, the pads are elliptical, and after overlapping copies, the lines and disc edges are hazy and deformed. If the user's appearance on the PCB is very strict, please use it with caution.
4. Photo method:
This method is only applicable to silver salt negatives. It can be used when it is inconvenient to re-drill the test plate and the deformation ratio of the film in the length and width directions is the same. The operation is also very simple: just use the camera to zoom in or out on the deformed graphics.
PS: Generally, the loss of the film is large, and it requires multiple debugging to obtain a satisfactory circuit pattern. Focus on the image to prevent it from being deformed.
5. Hanging method:
This method is suitable for the film that has not been deformed, and also prevents the film from being deformed after copying. The specific operation: remove the film from the sealed bag before copying it, and dry it for 4-8 hours under working conditions, let the film It has been deformed before copying, so after copying, the probability of deformation is very small. For the already deformed negative, other methods are needed.
Reminder: Because the film will change with the temperature and humidity of the environment, when drying the film, make sure that the humidity and temperature of the hanging place are consistent with the working place, and in a ventilated and dark environment, to avoid the film being damaged. Pollution.
All of the above are remedies after the deformation of the film. In fact, in actual operation, engineers should consciously prevent film deformation. Prevention is the most important. To prevent film deformation, we should be in the PCB copying process. The temperature will be strictly controlled at 22±2°C, the humidity will be 55%±5%RH, the cold light source or the aerator with cooling device will be used, and the backup film will be replaced continuously.