Why the film is easily deformed in the PCB process
(1) Temperature and humidity control failure
(2) The exposure machine temperature rises too high
(1) Normally, the temperature is controlled at 22 ± 2 ° C and the humidity is at 55% ± 5% RH.
(2) Using a cold light source or an aerator with a cooling device and constantly replacing the backup film
Second, the process of film deformation correction:
1. Under the condition of mastering the operation technology of the digital programming device, firstly, the negative film is compared with the drilling test plate, and the length and width of the deformation are measured. On the digital programming device, the length of the deformation is lengthened or shortened according to the deformation amount. The drilled test plate after lengthening or shortening the hole position is used to remove the deformed negative film, thereby eliminating the troublesome work of cutting the negative film and ensuring the integrity and accuracy of the graphic. Call this method "change the hole position method".
2. For the physical phenomenon that the negative film changes with the change of temperature and humidity of the environment, take the negative film in the sealed bag before copying the negative film, and hang it for 4-8 hours under the working environment condition, so that the negative film is deformed before copying, so that It will make the negative film after copying very small, which is called "drying method".
3. For the pattern with simple line, wide line width and large spacing, and irregular deformation, the deformed part of the negative film can be cut and re-spliced after the hole position of the control drilling test board, and then copied, which is called “splicing method”. .
4. Use the hole on the test board to enlarge the pad to de-deform the line piece to ensure the minimum ring width technical requirement. This method is called “pad overlap method”.
5. Proportionally enlarge the graphic on the deformed film, and re-lay the plate to make it known as the “texture method”.
6. Use the camera to enlarge or reduce the deformed figure, which is called “photographing method”.
Third, the relevant methods Note:
1. Splicing method:
Applicable: the film with less dense lines and inconsistent film deformation of each layer; especially suitable for the deformation of the solder mask and multilayer power supply ground film;
Not applicable: negative film with high wire density, line width and spacing less than 0.2mm;
Note: When cutting, try to minimize the damage to the wire and not damage the pad. When splicing and copying, you should pay attention to the correctness of the connection relationship.
2. Change the hole position method:
Applicable: The deformation of each layer is consistent. Line-intensive negatives are also suitable for this method;
Not applicable: The film is not uniformly deformed, and the local deformation is particularly serious.
Note: After using the programmer to lengthen or shorten the hole position, the hole position of the tolerance should be reset.
3, hanging method:
Applicable; a film that has not been deformed and prevents deformation after copying;
Not applicable: Deformed negatives.
Note: Dry the film in a ventilated and dark (safe or possible) environment to avoid contamination. Make sure that the air temperature is the same as the temperature and humidity at the work place.
4, the pad overlap method:
Applicable: The graphics lines are not too dense, and the line width and spacing are greater than 0.30mm;
Not applicable: In particular, the user has strict requirements on the appearance of the printed circuit board;
Note: The pad is elliptical due to overlapping copies. After overlapping copies, the halo and deformation of the edges of the lines and discs.
5, photo method:
Applicable: The deformation ratio of the film in the length and width directions is the same. When it is inconvenient to re-drill the test plate, only the silver salt film is applicable.
Not applicable: The film has different length and width deformation.
Note: Focus should be accurate when shooting, to prevent line distortion. The loss of the negative film is large. Under normal circumstances, it is necessary to have multiple adjustments to obtain a satisfactory circuit pattern.
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