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PCB Tech

PCB Tech

Analysis on the countermeasures to the deformation of the negative film in the process of copying the circuit board
2021-09-13
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Author:Aure

Analysis on the countermeasures to the deformation of the negative film in the process of copying the circuit board

In the process of PCB copying, there will be some special situations that make people dilemma, that is, some improper operations lead to the deformation of the negative, which is a dilemma, whether to continue, affect the quality and performance of the final PCB copy, or just discard it. No need to cause cost loss? In fact, there are ways to correct the deformed negatives. These methods include:

Splicing
PCB copy board to change the hole position method
Land overlap method
Photography
Hanging method
The above-mentioned methods are very important methods, so let's talk about these methods separately, hoping to help everyone.

  1. Splicing method:
    This method is suitable for the film that is not too densely packed and the deformation of the film of each layer is inconsistent, and the correction of the solder mask film and the film of the power source layer of the multilayer board is particularly effective. Specific operation: cut the deformed part of the negative film, re-splice it against the hole position of the drilling test board, and then copy it. Of course, this is for simple deformed lines, large line widths and spacing, and irregular deformations. Graphics; not applicable to negatives with high wire density, line width and spacing less than 0.2mm.
    PS: When splicing, pay attention to as little as possible to damage the wires and not to damage the pads. When revising the version after splicing and copying, pay attention to the correctness of the connection relationship.



Analysis on the countermeasures to the deformation of the negative film in the process of copying the circuit board


2. PCB copy board to change the hole position method:
This method is suitable for correcting the negative film with dense lines, or the uniform deformation of the negative film of each layer. Specific operation: 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 adjust the hole on the digital programming instrument according to the two deformations of the length and width. Position, adjust the drilled test board to cater to the deformed negative. The advantage of this method is that it eliminates the troublesome work of editing negatives, and can ensure the integrity and accuracy of the graphics. The disadvantage is that the correction of the negative film with very serious local deformation and uneven deformation is not effective.
PS: To use this method, you must first master the operation of the digital programming instrument. After using the programming instrument to lengthen or shorten the hole positions, you should reset the out-of-tolerance hole positions to ensure accuracy.

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

4. Photographic method:
This method is only suitable for 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 direction of the film is the same. The operation is also very simple: just use the camera to enlarge or reduce the deformed graphics.
PS: Generally, the film loss is more, and it needs to be debugged many times to get a satisfactory circuit pattern. When taking pictures, the focus should be accurate to prevent the lines from being deformed.

5. Hanging method:
This method is suitable for the undeformed negative film, and can also prevent the negative film from deforming after copying. The specific operation: take the negative film out of the sealed bag before copying, and let it hang for 4-8 hours under working environment conditions. It has been deformed before copying, so after copying, the probability of deformation is very small. For the film that has been deformed, other measures need to be taken.
Warm reminder: Because the film will change with the change of the environmental temperature and humidity, when hanging the film, make sure that the humidity and temperature of the hanging place is the same as that of the working place, and it needs to be in a ventilated and dark environment to prevent the film from suffering Pollution.
The above are all remedies after the film is deformed. In actual operation, engineers should still consciously prevent the film from deforming. Prevention is the most important thing. To prevent the film from deforming, we should use the PCB copying process. The temperature is strictly controlled at 22±2℃, the humidity is 55%±5%RH, cold light source or aerator with cooling device is used, and the backup film is constantly replaced. ipcb is a high-precision, high-quality PCB manufacturer, such as: isola 370hr pcb, high-frequency pcb, high-speed pcb, ic substrate, ic test board, impedance PCB, HDI PCB, Rigid-Flex PCB, buried blind PCB, advanced PCB, microwave PCB, telfon pcb and other ipcb are good at PCB manufacturing.