1. Check User Files
The files brought by the user must first undergo routine checks:
1. Check if the disk files are intact;
2. Check if the file is infected with a virus; if there is a virus, it must be removed first;
3. If it is a Gerber file, check if there is a D-code table or if it contains D-codes.
2. Check if the Design Meets Our Factory’s Process Standards
1. Check whether the various spacings designed in the customer’s file meet our factory’s process: spacing between lines, spacing between lines and pads, and spacing between pads. All these spacings should be greater than the minimum spacing that our factory’s production process can achieve.
2. Check the width of the traces; the width should be greater than the minimum line width achievable by our factory’s production process.
3. Check the size of the vias to ensure they meet the minimum hole diameter of our factory’s production process.
4. Check the size of the pads and their internal diameters to ensure that there is a certain width around the pad edge after drilling.
3. Determine Process Requirements
Determine various process parameters based on user requirements.
Process requirements:
1. Depending on the different requirements of subsequent processes, determine whether the photoplotting film (commonly known as film) needs to be mirrored. The principle of film mirroring: the photoresist side (i.e., the latex side) sticks to the photoresist side to minimize errors. The determining factor for film mirroring: the process. If it is a screen printing process or dry film process, then the photoresist side of the film should stick to the copper surface of the substrate. If using diazo film exposure, since diazo film copies are mirrored, its mirroring should be the photoresist side not sticking to the copper surface of the substrate. If the photoplotting is done with unit films instead of on a photoplotting film, an additional mirroring step is required.
2. Determine the parameters for the solder mask expansion.
4. Determine Principles
① The solder mask should not expose traces next to the pads.
② It should not cover the pads.
Due to operational errors, the solder mask may deviate from the traces. If the solder mask is too small, the result of the deviation may cause the pad edges to be covered. Therefore, the solder mask should be larger. However, if the solder mask is expanded too much, it may expose the adjacent traces due to the influence of deviations. From the above requirements, we can see that the determining factors for solder mask expansion are:
① The deviation value of our factory’s solder mask process position and the deviation value of the solder mask graphic.
Since the deviations caused by various processes are different, the solder mask expansion values corresponding to various processes are also different. For processes with larger deviations, the solder mask expansion value should be chosen larger.
② For boards with high trace density and small spacing between pads and traces, the solder mask expansion value should be chosen smaller; for boards with low trace density, the solder mask expansion value can be chosen larger.
3. Determine whether to process craft lines based on whether there are printed connectors (commonly known as golden fingers) on the board.
4. Determine whether to add conductive frames for electroplating based on electroplating process requirements.
5. Determine whether to add conductive craft lines based on hot air leveling (commonly known as tin spraying) process requirements.
6. Determine whether to add center holes for pads based on drilling process requirements.
7. Determine whether to process positioning holes based on subsequent process requirements.
8. Determine whether to add outline corner lines based on the board’s shape.
9. When users require high precision for line width, determine whether to perform line width correction based on our factory’s production level to adjust for the effects of undercutting.
5. Convert CAD Files to Gerber Files
In order to carry out unified management during the CAM process, all CAD files should be converted to the standard format Gerber for photoplotters and the corresponding D-code table.
During the conversion process, attention should be paid to the required process parameters, as some requirements must be completed during the conversion.
Currently, various commonly used CAD software, except for Smart Work and Tango software, can convert to Gerber. The above two software can also be converted to Protel format first and then to Gerber using tool software.
6. CAM Processing
Perform various process treatments according to the specified processes.
It is particularly important to check whether there are any areas in the user files where the spacing is too small, which must be addressed accordingly.
7. Photoplotting Output
After the files have been processed by CAM, they can be output for photoplotting.
The work of panelization can be carried out in CAM or during output.
A good photoplotting system has certain CAM functions, and some process treatments must be performed on the photoplotter, such as line width correction.
8. Darkroom Processing
The photoplotting film must be developed and fixed before it can be used in subsequent processes. During darkroom processing, the following aspects must be strictly controlled:
Development time: affects the light density (commonly known as darkness) and contrast of the production base plate. If the time is too short, the light density and contrast will be insufficient; if the time is too long, it will lead to increased haze.
Fixing time: if the fixing time is insufficient, the base plate will not be sufficiently transparent.
Washing time: if the washing time is insufficient, the production base plate is prone to yellowing.
Special attention: Do not scratch the film’s photoresist.
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