More about PCB artwork

Above: the most common PCB pads used by the instructor, along with the real parts for comparison. There is nothing special about these pads, anyone can make their own, subject to these restrictions: if there are through-board holes like for the modular jack or .025" square pins, you must have the hole spacings just right; size 1206 (resistors and caps) can have one wire go through the middle, that is very handy for reducing jumpers; zener pads can take two wires between the pads; spacing between pads must be enough that your personal etching process doesn't create lots of shorts. A four-times enlargement of this .jpg file can be requested from the instructor. It is file name surface mount pads SMD 200dpi.jpg and it is on the GRID computer on the Ubuntu side, also on GETTER. The instructor uses the commercial, expensive drawing software CorelDRAW because he is used to it. The Linux drawing software, free, is Inkscape. So is Open Office Draw. Whatever software you use, there is a steep learning curve.

The parts for purchase at 12311 Culebra Road #6104 San Antonio are at https://sites.google.com/site/solderandcircuits/home/buy-some-parts-in-class

An example of a full layout is at https://sites.google.com/site/solderandcircuits/home/ac-coupled-light-receiver

Whether you use computer graphics or do hand drawing on paper, you draw wires with black lines. MG Chemicals’ process is "positive," so your black lines will end up as copper wires. The white area of your "artwork" will cause the .0015"-thick copper to etch away in fifteen minutes, using ferric chloride.

Every electronic part and connector will need "pads." A library of common pads is available from the instructor. You can add your own creations.

You create your circuit by looking at your schematic and hooking up wires between pads.

There will be plenty of places where you cannot "route" a wire because another wire is in the way. (You are probably doing "single-sided" boards, not double-sided.) Just put in circle pads so you can solder on insulated wires as "jumpers."

The common "connectors" are

• 1. .1"-spaced pins, either male or female. If male, you choose single row or dual row. If female, it is dual row. A sample part from the Mouser catalog is FCI Company part number 68001-136HLF which is 36 gold-plated pins, single row, $.86. These male pins are square, .025" on a side, .1" spacing.

  2. RJ-45 jack, the jack used for Ethernet cabling. This is a great connector but you have to be careful about which end is orange-white and which is brown. The order is orange-white, orange, green-white, blue, blue–white, green, brown-white, brown. This order is seen in any category 5 or 5-E cable—have a cable beside your computer as you are designing your board. The pads are viewed from the bottom! To go from your board to soldered wire connections, buy a cheap Ethernet calbe and cut it in half.

  3. You may skip connectors and just solder wires to .1"-diameter pads.

Any pad that will have a wire or connector pin needs to have a white dot in the middle, about .015" diameter. This will be an etched-away spot in the pad to guide your drill bit. This is an extreme advantage to get neatly drilled holes.

Your first three board designs will not be so great, there is a lot to learn.

Put some text on your board: your name, date, name of your project, resistor and capacitor values, names of cables. Show the number of any integrated circuit, and show a 1 for pin one on any integrated circuit. You will look at your board in 30 years and be amazed at what you did.

A tricky step is mirroring (flipping) your art work just before printing to transparency. The reason is that the black toner must be on the bottom of the transparency, in contact with the blue "resist" on your MG Chemicals board, whereas the printer puts toner on top of the transparency. So all we do is flip your artwork in Open Office Draw, in one step, and print that, then flip the transparency over to expose the board.

Here is a detail about the flip. Before you EDIT, SELECT ALL, and MODIFY FLIP, you have to select each text object and convert to curves. Then SELECT ALL and FLIP.

Warning—make a copy of your work, with a slightly different name, before converting text to curves. Once converted, you cannot edit the text anymore.

Etching is a major job. There is a lot of setup. So we wait to etch until several people can etch at once. You are free to order MG Chemicals supplies on your own, but the developer is corrosive sodium hydroxide (Drano) and the ferric chloride stains everything except glass. The ferric chloride also is toxic because it is loaded with iron and copper. "Developing" with sodium hydroxide is a tricky step. My experience is that if you have several boards to process, for some reason it doesn't work to make a bigger batch of developer and pass consecutive boards through the same solution. What does work is to make small batches, like 2 tsp concentrate to 20 tsp warm water, and discard after developing each board. Controlling the temperature to around 110 degrees F helps so much, by setting your glass develop dish down into another one that has hot water. But don't get too hot, the exposed blue resist will all dissolve. Ferric chloride temperature can be hotter and is all around less tricky than developing.

Getting good exposure, using UV-A tubes, is tricky. The instructor has a great set up to do this for you. The entire etch process is in-house as of August, 2012. I found that translucent vellum passes enough UV, and has enough contrast with a laser printer, to bypass going to a copy shop to get a transparency of the artwork. However, the older laser printer I have does not have uniform density on big black areas, I have been taking a pencil to the vellum to improve the density of the big black areas. Exposure time has settled down to 32 minutes using vellum vs. 23 minutes for copy-shop transparency.

A 6" x 9" board from MG Chemicals is about $15.00. You can get several projects onto one board and hacksaw them apart.

Electronics is not the only use for printed circuit boards. Artists can do art and etch it onto printed circuit boards, then backlight the fiberglass board for a neat effect.

Frustration Alert

Open Office Draw, useful for creating a printed circuit board, has a steep learning curve and is frustrating but usable. To avoid carpal tunnel syndrome, it should be used with a USB drawing tablet, such as the Wacom brand. Do not try using a laptop’s little trackpad, even a USB mouse is better than that.

Alternatives:

• • You can do hand drawings on paper, using vinyl electrical tape to create pads and a broad-tip Sharpie to make lines. Do this at 4x enlargement, then reduce with a copier, or scan and reduce with Photoshop and touch it up on Photoshop or with Open Office Draw.

  • CorelDRAW or Adobe Illustrator are expensive but are easier to control with a drawing tablet than Open Office Draw. Learning one of these professional tools has lifelong benefits.

  • Use a file e-mailed from the instructor johnenge@earthlink.net, 7x surface mount.pdf on GETTER computer. Print it with no scaling (do not fit to page) so that the 1" reference bars come out 7" long. Cut out "paper dolls" and tape parts onto white paper. Scan this and reduce it so the 1" reference bars are now 1". Threshold this to white/black, flip it, and print to vellum. Proceed with exposure and etch. The 7x surface mount.pdf is depicted following, but request the original for your own work. The 1206 parts are a good size of resistor and capacitor to use. They show one trace going between the solder pads, which may help you connect various parts of your circuit. The diode and zener pads can handle two auxiliary traces, and the SOT-23 transistor handles one. Use the round pads for through-board, leaded components and for wires. Purchase your parts cheap from the instructor.

The photo above shows the schematic below being pieced together at 7x. Tape these down as you go, it will look a lot better than the photo above. Once your layout looks good, you can use a permanent marker to do any patch-up that is needed. Add your name, date, and name of the board. Above, notice that the ground trace is snaking up through the diode at the top. This process, doing 7x layout with paper shapes, was successful second week of Oct 2013 to make a one-stage audio amp with $1.70 electret mic on the board, with minimum feature size .017", with cheap surface-mount parts on a 1.6"-square board. The work is by a sixth grader guided by Mr. Engelbrecht, with parent present. The tricky part was scanning and 7x shrink. Scan was with my HP Scanjet G4050 and HP software, which offered 1-bit, B&W color depth, ideal for PCB work. I found out the hard way that the initial scan should be at 600dpi, not at 96 or 200 dpi. Using 600dpi from the start lets you clean up the scan on Corel Photopaint in Windows or The Gimp in Linux, then you resample or scale to 16%, flip, copy to 8.5x11 page size, do two tiny black rectangles on opposite corners of the 8.5x11 to preserve the page size, do .pdf output, and print to laser printer. These steps are pretty much beyond what MS Windows Paint can do. I know it works with Corel Photopaint, and I think the free The Gimp can do it.