Analysis of Film Deformation in PCB Process
First, the film deformation causes and solutions:
(1) Failure of temperature and humidity control
(2) Exposure temperature rises too high
(1) Normally the temperature is controlled at 22±2°C and the humidity is 55%±5%RH.
(2) Using a cold light source or an aerator with a cooling device and constantly replacing the backup film
Second, the film deformation correction process method:
1. Under the condition of mastering the operation technology of the digitizer, the first negative film is compared with the borehole test plate to measure the length and width of the two deformations. The digitizer is used to lengthen or shorten the hole position according to the deformation amount. , With the borehole test plate after lengthening or shortening the hole position to meet the deformation of the film, eliminating the tedious work of cutting the film, ensuring the integrity and accuracy of the graphics. Call this method "change hole method."
2. For the physical phenomenon that the film changes with the change of temperature and humidity of the environment, take the negative film in the sealed bag before taking the copy film, and hang it for 4-8 hours under the working environment, so that the film is deformed before copying. The film will be deformed after the copy is very small, saying this method "hanging hanging method."
3, for the circuit is simple, line width and spacing larger, irregular deformation of the graphics, can be used to cut the deformation of the film section of the borehole of the control drilling test board to re-splicing and then copy, call this method "splicing method" .
4. Use the holes on the test board to magnify the pads that are heavily deformed into pads to ensure the minimum ring width requirement. Call this method “pad overlap method”.
5. Scale up the deformed film on the film and re-plate it. Call this method “map method”.
6. Use a camera to enlarge or reduce the deformed image, and call this method “photographing method”.
Third, related methods note:
1, splicing method:
Applicable: The film is not dense, the film of each layer is inconsistent in deformation, and it is especially suitable for the deformation of the solder mask and multilayer power plate.
Not applicable: film with high density of wires, line width and spacing less than 0.2mm;
Matters needing attention: When the splicing should be as little as possible injury, do not hurt the pad. When splicing and copying, it is necessary to pay attention to the correctness of the connection relationship.
2, change the hole position method:
Applicable: The deformation of the film in each layer is the same. Line-intensive negative film also applies this method;
Not applicable: The film is not uniformly deformed, and local deformation is particularly serious.
Note: After using the programmer to extend or shorten the hole position, the hole position should be reset.
3, hanging hanging method:
Applicable; film that has not been deformed and prevented from being deformed after copying;
Not applicable: Deformed negatives.
Matters needing attention: In the ventilation and dark (safety can also be) environment hanging film, avoid and pollution. Make sure that the temperature and humidity of the hanging place and the work place are the same.
4, pad overlap method:
Applicable: graphics circuit is not too dense, line width and spacing greater than 0.30mm;
Not applicable: In particular, the user's appearance on the printed circuit board is strictly required;
Note: The pads are elliptical due to overlapping copies. The halo and deformation of the line and disc edge after overlapping copies.
5, photo method:
Applicable: The deformation ratio of the length and width of the film is the same, so it is only suitable for the silver salt film when re-drilling the test plate;
Not applicable: Inconsistent deformation of the length and width of the film;
Matters needing attention: The focus should be accurate when taking photos, to prevent line deformation. The loss of the film is relatively high. Under normal circumstances, it is necessary to have many times of debugging to obtain a satisfactory circuit pattern.
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