Analysis of film deformation problem in PCB process

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Analysis of film deformation problem in PCB process [Copy link]

1. Causes and solutions for film deformation:

　　Cause:
　　(1) Temperature and humidity control failure
　　(2) Exposure machine temperature rise is too high
　　Solution:
　　(1) Normally, the temperature is controlled at 22±2℃ and the humidity is controlled at 55%±5%RH.
　　(2) Use cold light source or exposure machine with cooling device and constantly replace backup film

2. Process method for film deformation correction:

　　1. After mastering the operation technology of the digital programmer, first install the film and compare it with the drilling test board, measure the deformation of its length and width, lengthen or shorten the hole position on the digital programmer according to the deformation, and use the drilling test board with the lengthened or shortened hole position to match the deformed film, eliminating the tedious work of editing the film and ensuring the integrity and accuracy of the graphics. This method is called the "hole position change method".
　　2. In view of the physical phenomenon that the film changes with the changes in ambient temperature and humidity, take out the film in the sealed bag before copying the film, and hang it in the working environment for 4-8 hours, so that the film will be deformed before copying, so that the deformation of the copied film will be very small, which is called the "hanging method".
　　3. For graphics with simple circuits, large line width and spacing, and irregular deformation, the deformed part of the film can be cut open and re-spliced with the hole position of the drilling test board before copying, which is called the "cutting method".
　　4. Use the holes on the test board to enlarge the pads to remove the deformed circuit pieces to ensure the minimum ring width technical requirements. This method is called the "pad overlap method".
　　5. After the deformed pattern on the film is enlarged in proportion, it is re-pasted and plated. This method is called the "painting method".
　　6. Use a camera to enlarge or reduce the deformed pattern. This method is called the "photographic method".

3. Notes on related methods:

　　1. Splicing method:

　　Applicable: films with not too dense circuits and inconsistent deformation of each layer; especially suitable for deformation of solder mask films and multi-layer board power supply layer films;
　　Not applicable: films with high wire density and line width and spacing less than 0.2mm;
　　Note: When cutting, try to minimize the damage to the wires and pads. When revising the version after splicing and copying, pay attention to the correctness of the connection relationship.

　　2. Change hole position method:

　　Applicable: The deformation of each layer of film is consistent. This method is also applicable to films with dense circuits;
　　Not applicable: The deformation of the film is uneven, and the local deformation is particularly serious.
　　Note: After using the programmer to lengthen or shorten the hole position, the hole position that exceeds the tolerance should be reset.

　　3. Hanging method:

　　Applicable: Film that has not been deformed and will not be deformed after copying;
　　Not applicable: Film that has been deformed.
　　Note: Hang the film in a ventilated and dark environment (safety is also acceptable) to avoid contamination. Ensure that the temperature and humidity of the hanging area are consistent with the work area.

　　4. Pad overlap method:

　　Applicable: Graphic circuits are not too dense, line width and spacing are greater than 0.30mm;
　　Not applicable: Especially when users have strict requirements on the appearance of printed circuit boards;
　　Note: After overlapping copying, the pad is elliptical. After overlapping copying, the halo and deformation of the edge of the line and pad.

　　5. Photography method:

　　Applicable: The deformation ratio of the length and width of the film is consistent. When it is inconvenient to re-drill the test board, only silver halide film is applicable.
　　Not applicable: The deformation of the length and width of the film is inconsistent.
　　Note: The focus should be accurate when taking pictures to prevent line deformation. The film loss is high. Usually, multiple debugging is required to obtain a satisfactory circuit pattern.

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