PCB Blog - The operation process of PCB board photopainting (CAM)

About the operation process of PCB board light painting:
1. Check the user's files
The files brought by the user must first be checked routinely:
1) Check whether the disk file is intact;
2) Check whether the file has an asterisk, if there is an asterisk, you must kill the asterisk first;
3) If it is a Gerber file, check whether there is a D code table or a D code inside.

2. Check whether the design conforms to the technical level of our factory
1) Check whether the various spacings designed in the customer's documents conform to the factory's process: the spacing between lines and lines, the spacing between lines and pads, and the spacing between pads and pads. The above various spacings should be greater than the spacing that can be achieved by the factory's production process.
2) Check the width of the wire, it is required that the width of the wire should be larger than the line width that can be achieved by the production process of our factory.
3) Check the size of the via hole to ensure the aperture of the factory's production process.
4) Check the size of the pad and its internal aperture to ensure that the edge of the pad after drilling has a certain width.

3. Determine the process requirements
Various process parameters are determined according to user requirements. Process requirements:
3.1 According to the different requirements of the subsequent process, determine whether the light-painted negative (commonly known as film) is a mirror image. The principle of film mirroring: paste the film on the film surface to reduce the error. The deciding factor of the mirror image of the negative film: the process, if it is a screen printing process or a dry film process, the film surface of the negative film and the copper surface of the substrate shall prevail. If it is exposed with a diazo film, since the diazo film is mirrored during copying, the mirror image should be that the film surface of the negative film is not attached to the copper surface of the substrate. Additional mirroring is required if photopainting is done as a unit negative rather than imposition on a photopainted negative.
3.2 Determine the parameters of solder mask expansion.
Determination principles: 1) Do not expose the wires next to the pads. 2) Small can not cover the pad. Due to errors in operation, the solder mask map may deviate from the circuit. If the solder mask is too small, the result of the deviation may be masking the pad edge. Therefore, the solder mask is required to be larger. However, if the solder mask expands too much, the adjacent wires may be exposed due to the influence of deviation.

From the above requirements, it can be seen that the determinants of solder mask expansion are:
1) The deviation value of the solder mask process position of our factory and the deviation value of the solder mask pattern. Due to the different deviations caused by various processes, the solder mask expansion values corresponding to various processes are also different. The solder mask expansion value with large deviation should be selected larger.
2) If the wire density of the board is high, the distance between the pad and the wire is small, and the expansion value of the solder mask should be smaller; if the wire density of the board is small, the expansion value of the solder mask should be larger.
3) According to whether there are printed plugs (commonly known as gold fingers) on the board to determine whether to add process lines.
4) Determine whether to add a conductive frame for electroplating according to the requirements of the electroplating process.
5) According to the requirements of the hot air leveling (commonly known as tin spraying) process, determine whether to add conductive process lines.
6) Determine whether to add the center hole of the pad according to the drilling process.
7) Determine whether to add process positioning holes according to the subsequent process.
8) According to the shape of the board, determine whether to add the shape angle.
9) When the user's high-precision board requires high line width accuracy, it is necessary to determine whether to perform line width correction according to the production level of our factory to adjust the influence of side erosion.

4. Convert CAD files to Gerber files
In order to carry out unified management in the CAM process, all CAD files should be converted into Gerber standard format of light plotter and equivalent D code table. During the conversion process, attention should be paid to the required process parameters, because some requirements are to be completed during the conversion. In the current general CAD software, except Smart Work and Tango software, can be converted to Gerber, the above two software can also be converted to Protel format through tool software, and then converted to Gerber.

5. CAM processing
Various process treatments are carried out according to the specified process.
Special attention should be paid to whether there are any places in the user file that are too small and must be dealt with accordingly

6. Light drawing output
The files processed by CAM can be output by light drawing. The work of imposition can be carried out in CAM or at output. A good photoplotter system has certain CAM functions, and some process processing must be performed on the photoplotter, such as line width correction.

7. Darkroom processing
The light-painted negative film needs to be developed and fixed before it can be used in the subsequent process. When processing in the darkroom, the following links should be strictly controlled: development time: affecting the optical density (commonly known as blackness) and contrast of the production master. If the time is short, the optical density and contrast are not enough; if the time is too long, the fog will increase. Fixing time: If the fixing time is not enough, the background color of the production base is not transparent enough. Unwashed time: If the washing time is not enough, the production plate will easily turn yellow. Special attention is not to scratch the film of the PCB board negative.