Production of a printed circuit board photomask. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies

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In the technological process of industrial production of photomasks for the production of printed circuit boards, special expensive equipment is used, which not every enterprise can afford to purchase. Therefore, many designers-developers and radio amateurs have to look for cheaper ways to make printed circuit board photomasks.

One of these methods is the manufacture of a photomask on a laser printer. Any laser printer with a resolution of 600x600 dpi (42 microns) is enough to get a high-quality black-and-white printout of the pattern of printed conductors, which will be used as a photomask. These are, in particular, Hewlett-Packard LaserJet 5L and LaserJet 1100 printers.

If in the computer-aided design of printed circuit boards ACCEL EDA (P-CAD 2000) there are no special problems with displaying information on the printer, then for adherents of P-CAD v4.5, not everything is so simple. Before printing a printed circuit board drawing on a printer, you need to use the PC-CARDS program to obtain a PLT file from the existing source file with the PCB extension. Then you should download the PC-PRINT program and set the following configuration:

• PC-PRINT Configuration: Default configuration.....PC-PRINT.CFG
• Printer port.....LPT1
• Output device.....disk
• Memory size (Laser Printers Only).....1024Kb
• Default printer.....LaserJet+Printer(HP)
• Default paper size.....A
• Graphics density.....high
• Plot.....slow
• Text dimensions (% of text size): Text character width (including space).....70%
• Text character height.....80%
• Space below text line.....10%
• Space above text line.....10%
• Space from top of text to bar.....20%

After saving the above configuration in the pcprint.cfg file, then use the previously obtained PLT file. But first, let's consider the main configuration parameters separately:

1. Output device - the output device must be disk. In this case, the result of the program will be saved on the hard drive as a file, regardless of whether a laser printer is connected to the computer or not.

2. Default printer - LaserJet+Printer(HP) must be selected as the printer. As a result, files on the hard drive will be saved with the HPP extension. The resulting files can be copied to any computer with a connected laser printer, even if P-CAD v.4.5 is not installed there, and printed by typing the following on the command line: copy filename.hrp prn.

3. Memory size - the amount of memory, by default - 64 KB, which is clearly not enough. Therefore, the volume should be increased to 1024 KB, otherwise the template will not print completely on the printer.

4. Default paper size - set the paper size for the required template format. Possible values ​​of this parameter correspond to the following standard: A - A4. B - A3, C - A2, D - A1, E - AO. Since the printer format is A4, when you specify the value B, the printout of the template will be displayed on two sheets, with the value C - on four sheets, etc. This is because the PC-PRINT program "can" split the drawing into parts.

5. Graphics density - graphics density can be set in three options: low - low, 120 dpi; medium - medium, 240 dpi; high - high, 300 dpi.

6. Plot - set one of two drawing methods: fast - fast, slow - slow. With the fast method, conductors and polygons (large sections of foil) are not filled, only their outer contour is displayed.

Unfortunately, laser printers, due to their low resolution, draw a template with a certain error. The programs with the help of which the final information product is obtained, and the programs that output information to the printer also contribute their share here. So it was found that when outputting files with the HPP extension, the conductors located on the template at an angle of 45 degrees with respect to any of the axes are filled with reduced contrast or not filled at all. Therefore, you have to additionally retouch the templates (with ordinary black ink or a black felt-tip pen).

You can print the template on a laser printer in a slightly different way. Files of the PLT format are not converted using the PC-PRINT program into files with the HPP extension, but are used to obtain the PSC format, i.e. PostScript, from them. The resulting PostScript files are then converted to PCX graphics format and output to the printer in the usual way using a graphics editor such as Corel PHOTO-PAINT from the CorelDRAW v9.0 package. This gives great opportunities compared to the way of outputting files with the HPP extension - all conductors are filled in completely, it is possible to make both a negative and a positive image, change its mirroring and scale. Details about this transformation can be found in [1].

PostScript files can be directly output to a printer without being converted to PCX graphics format. However, this requires that the laser printer understand the PostScript language at the hardware level, i.e., the printer must be equipped with a PostScript language interpreter.

You can use plain paper, synthetic tracing paper for a pencil, or special transparencies for HP LaserJet laser printers (not to be confused with thermal paper for fax or photo paper for inkjet printers) as the basis for the template. The film is sold in packs of 50 and 100 A4 sheets.

If there are no problems when printing on paper, then synthetic tracing paper has to be fed into the printer paired with a sheet of paper. Moreover, at the tracing paper, the input edge must be folded back by 2 ... 3 cm, and a sheet of paper should be inserted into the fold. Print, of course, should be on the matte side of the tracing paper. Thus, it is possible to deceive the printer and print a printed circuit board drawing on a tracing paper not intended for this with high quality.

If the printed image comes out with insufficient contrast, it can be enhanced by treating the sheet with acetone vapor for some time. This will require a suitable size flat shallow cuvette made of a material resistant to acetone (glass, polyethylene, vinyl plastic, carbolite, metal). The edges of the cuvette should be even so that it can be covered with a lid to reduce the loss of acetone by evaporation.

Pour enough acetone into the cuvette to cover the bottom. The template is attached to the inside of the lid with an image to acetone, either with small magnets (if the lid is steel) or with tape. Attachment points should be located on the margins of the template. Cover the cuvette with a lid and periodically visually check the condition of the image, achieving the desired effect. In no case should the surface of the template be wetted with acetone.

The contrast of the printout can also be changed programmatically, if the printer allows.

In the case when the drawing is printed on ordinary printer paper, it can be treated with special chemical aerosols to make it transparent [2].

The technology for manufacturing printed circuit board photomasks described above should be used only when the boards, including double-sided ones, are supposed to be drilled manually, without the use of special CNC machines. In this case, the drill is unlikely to hit the center of the contact pads on the board blank. At the same time, for amateur radio development or for small-scale production, where holes on the boards can be drilled manually, the accuracy of such a technology is quite sufficient.

In order to increase the convenience and accuracy of PCB drilling, contact pads at the drawing stage in the PC-CARDS program should be made not solid, but with a white circle with a diameter of 0,5 ... 0,7 mm in the center. As a result, the drill will be easier to place on the center of the site before drilling the hole.

Literature

1. Goryachkin A. Converting P-CAD files to graphic formats. - Radio, 2002, No. 1, p. 24.
2. PCBs made easy! - Radio, 2001, No. 3, p. 46.

Author: A. Goryachkin, Kyshtym, Chelyabinsk Region

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