Printed Circuit Artwork

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The artwork for the printed circuit board is available in GIF format.  Copies of both the copper layer and the silkscreen overlay may be downloaded.  (Some internet browsers may not display/print these images properly, so I recommend downloading the files and printing from an external editor such as IrfanView).  The printed images should measure 2.5" wide x 2.0" high;  each image is 750 x 600 pixels and can thus be printed at 300dpi resolution with no post-processing necessary.  However, if you must print at a higher or lower resolution, simply scale the image appropriately with one of the graphic editors mentioned above.  Note there is no benefit from printing at a higher resolution because the printout can be only as good as the original image.

The printed circuit artwork is also available in Adobe Acrobat PDF format.  Please download the file here.  This format greatly simplifies printouts, however the silkscreen text does not display as clearly as the GIF.

Most individuals interested in etching their own boards will probably have a favorite PCB fabrication method.  However, following is a quick and dirty description of two of the more popular techniques for do-it-yourself printed circuit boards:  the photo development method and the toner transfer method.

Photo Developing Printed Circuit Boards
This method involves printing the positive artwork on transparent film, placing it over a special photosensitive PCB and exposing the assembly to light.  The copper layer artwork should be placed such that the "ink" side is against the copper.  This prevents light from diffusing around the ink and through the transparent stock, which would yield poorly defined copper traces.  The board is coated with an etch resistant layer that breaks down when exposed to a strong light source for about five minutes.  After exposure, place the board into a mild chemical "developer" bath to remove the etch-resistant material from all the areas which were exposed to light.  The protective etch-resist coating will remain on those areas which were concealed by the artwork, which are soon to be our printed circuit traces.  Submerge the board in ferric chloride and agitate continuously to remove the exposed copper areas.  Finally, expose the board to light again to weaken the remaining etch-resist on the copper traces.  One more dip into the developer bath reveals the clean copper traces and the board is ready for drilling.  I've used this method often and it works very well.  The primary drawbacks are the cost of the photosensitive boards (which are about 2-3x as much as a bare copper board) and having to purchase an additional chemical to develop the board.  The type of printer (laser/inkjet) is unimportant as long as it can generate good, opaque artwork on Vellum or transparency stock.

Printed Circuit Boards by Toner Transfer
The second method involves printing the artwork onto a plastic film with a laser printer.  Then using a regular clothes iron, the toner may be transferred directly onto a bare copper board.  The toner protects the traces during etching in ferric chloride.  After etching, the toner can be removed from the copper traces with acetone.  It probably goes without saying, but one must make sure the material the artwork is printed onto is NOT a thermoplastic, otherwise it will ruin the laser printer!  And of course, the material must be "slick" or the toner won't transfer onto the copper properly.  There is a material sold specifically for this purpose (read: expensive), but standard transparencies will work well if you're only making a couple of boards.  Again, it is important to ensure the printout is the best possible quality to prevent damaged or broken traces on the finished board.

Be sure the artwork is in the proper orientation, which depending on how it was prepared, may need to be mirror imaged so the toner will rest against the copper.  Prepare the bare copper board by roughing it up with 400 grit sandpaper.  Then place the toner side against the copper and tape it liberally into place, being sure to pull it as tight against the copper as you possibly can to avoid any shifting while ironing.  I cannot overemphasize the importance of this step--if you are not careful, the artwork will shift and you run the risk of a poor quality transfer or bridged traces on the etched board.

Place the assembly on a hard, flat worktable.  The heat required is intense, so definitely don't do this on the kitchen table.  Cover the transparency with a sheet of notebook paper as a buffer to be sure the plastic doesn't melt.  It can take a surprising amount of heat, and the notebook paper will begin to burn before the transparency melts.  Ramp your iron onto its highest setting and turn off any steam features.  Iron slowly and with as much pressure as you can muster, as the toner does not transfer immediately.  After you've ironed for a bit, gently lift up a corner and see if the toner has adhered to the copper.  If not, continue ironing.  Once you feel comfortable that the toner has adhered uniformly, leave the assembly to cool *fully*.  If it is tampered with before cooling, there will be areas where the toner pulls away from the board when the transparency is peeled away.  Inspect the board and touch up any damaged areas with a laundry marker.  Now submerge the board in ferric chloride and agitate the solution until the board is fully developed.  Remove the board and rinse in water.  A little acetone will remove all of the toner, revealing the clean copper traces.

Here's a similar method you may want to try:  use a coated paper rather than transparency.  Some premium inkjet and laser papers (typically 70 lb stock or greater) have a smooth clay coating that makes it well-suited to this purpose, and which is much less expensive than transparencies.  After the toner has been ironed onto the board (and cooled), simply soak it in hot water to break down the paper.  The clay coating separates from the paper and allows the toner to remain behind.  Then etch in ferric chloride as described above.  The nice thing with this method is that when the toner is "re-flowed" by heating, it effectively fills in any pitting that is visible in the original artwork.  The caveat, however, is a limited track-to-track spacing.  If two traces or pads are located close together, there is a possibility that they will bridge together when the toner is remelted.  If this happens, simply use an X-acto® knife to scrape away any stray toner before etching.

Note on the artwork that the solder pads have visible holes.  These holes facilitate drilling by leaving a small dimple in the copper pad, guiding the drill bit into the center of the pad.  A 33mil bit may be used to drill the holes for component leads.  This size is large enough to insert all components easily, while also leaving an adequate annular copper ring of which to solder.

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Revised January 27, 2006
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