Solution to the problem of negative film deformation in PCB process

by:A-TECH      2021-03-15
1. The cause of film deformation and the solution:    Cause:    (1) Temperature and humidity control failure (2) Excessive temperature rise of the exposure machine Solution:    (1) Normally the temperature is controlled at 22±2℃, and the humidity is 55%±5 %RH. (2) Adopt a cold light source or an aerator with a cooling device and constantly replace the backup film. Second, the process method of film deformation correction:    1. Under the condition of mastering the operation technology of the digital programming instrument, first install the film and contrast the drilling test board. Measure the length and width of the two deformations, lengthen or shorten the hole position according to the deformation amount on the digital programming instrument, and use the drill test board after the lengthening or shortening of the hole position to adapt to the deformed negative film, eliminating The cumbersome work of editing negatives ensures the completeness and accuracy of the graphics. Call this method 'change hole position method'. 2. In view of the physical phenomenon that the negative film changes with the environmental temperature and humidity, take out the negative film in the sealed bag before copying the negative film, and hang it for 4-8 hours under the working environment, so that the negative film will be deformed before copying. It will make the negative film after copying very small, and this method is called 'hanging method'. 3. For graphics with simple lines, large line widths and spacing, and irregular deformations, you can cut the deformed part of the negative film to contrast the hole positions of the drill test board and re-splice before copying. This method is called 'splicing method' .  4. Use the holes on the test board to enlarge the pads to remove the heavy deformation of the circuit piece to ensure the minimum ring width technical requirements. This method is called the 'pad overlap method'.   5. After scaling up the graphics on the deformed film, re-map and make a plate, call this method 'map method'.  6. u200bu200bUse a camera to enlarge or reduce the deformed figure. This method is called 'photographic method'. 3. Precautions for related methods:   1. Splicing method:   Applicable: the circuit is not too dense, and the negative film deformation of each layer is inconsistent; it is especially suitable for the deformation of the solder mask film and the bottom film of the power layer of the multilayer board; Negative film with line width and spacing less than 0.2mm;    Note: When splicing, the wires should be damaged as little as possible and the pads should not be damaged. When revising the version after splicing and copying, attention should be paid to the correctness of the connection relationship.  2. Method of changing the hole position:   Applicable: The deformation of each layer of the film is the same. This method is also applicable to film with dense lines;    does not apply: the film is not uniformly deformed, and the local deformation is particularly serious.   Note: After using the programming instrument to lengthen or shorten the hole position, the out-of-tolerance hole position should be reset.  3. Hanging method:   applicable; negative film that has not been deformed and prevented from being deformed after copying;   not applicable: deformed negative film.   Note: Hang the film in a ventilated and dark environment (safety is also possible) to avoid contamination. Ensure that the temperature and humidity of the hanging place is the same as that of the working place. 4. Land overlap method:   applicable: the pattern lines are not too dense, and the line width and spacing are greater than 0.30mm;   not applicable: especially the user has strict requirements on the appearance of the printed circuit board;   Notes: the pad is elliptical after overlapping and copying . After overlapping and copying, the halo and distortion of the edge of the line and disk.  5. Photographic method:   Applicable: The film has the same deformation ratio in the length and width directions, and when it is inconvenient to drill the test board, only the silver salt film can be used.   Not applicable: The length and width direction of the negative film is not deformed.   Note: The focus should be accurate when taking pictures to prevent distortion of the lines. The film loss is more, usually, it is necessary to debug several times to obtain a satisfactory circuit pattern. Here to enter the pcb pricing page https://www./
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