Let's Make Robots!

Making Boards(PCBs)

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Making your own printed circuit boards(PCB) is so easy now. The biggest change is in the resist coating on the boards. Now it is less sensitive to ambient light. You do not need a safety light or a closed room to work with these new boards. You do have to be careful with direct light from any source for more than a minute or so. You do not need a special bulb to expose them. Sunlight or a fluorescent light works best. Plan your space. I closed my bedroom blinds early in the afternoon and placed the exposer frame under my desk. I put a towel over my bathroom window where I have the development tray filled and set up. That’s it.

One thing that is important is that the resist is now sensitive to heat. Any heat. In its package under direct sunlight will kill your board. Keep them in a cool dark place. Heat is good thing too. When you are done developing your board you just rinse the board under warm water and that fixes the resist. Caution here. Once the resist is fixed it is not sensitive to the developer or the light anymore. 91% Isopropyl Alcohol cleans off the resist or you can fix errors or do modifications all in normal light.

The DATAK Boards use the same developer. They require a Hot 100 – 110 degree water development and a Cold water rinse to fix the resist. They can be exposed with standard 100 watt bulb at 12 inches for about 10 – 15 minutes.

 

One downside to these Single Fluorescent Tube exposer frames is that good exposer light is just three inches wide down the length of the tube. A 4x6 board set at the front of the exposer frame will have its back one inch edge poorly exposed. You must rotate your board. For Big boards just move them three inches each step through the exposer. About 6-8 minutes per step. You can get larger multi-tube exposer frames and special exposer lights.

Jameco.com has everything to make a PCB at home. Positive resist boards, Positive Developer, Etchant, trays and an exposer frame. Look under Electronic Design - Prototyping Systems. Pre-Sensitized boards are Printed Boards in many sizes. More Products has PCB kits and stuff. I have a single 17” fluorescent tube exposer frame. Mine is about 5 ½” high. I got it at Fry’s in Burbank, Ca. I also got my Ammonium Persulphate etchant at Fry’s. Read the instruction that comes with the boards. A good exposer makes a good PCB.

Print the PDF file at 100% or make art on clear transparency sheets. For laser printers print on the smooth side of the transparency sheet. Cut out the circuit on the board’s outline.

Step 1 Supplies and set up

  • Circuit print out or art work is just art work here
  • Art Work or Circuit pattern or PDF
  • Exposer Frame for the art work is the art frame here
  • Positive Resist Pre-Sensitized Board to fit you art work
  • Positive Developer
  • Etchant Exposer Frame or set up
  • I am using a single fluorescent tube exposer frame. A vary common exposer frame found in most PCB kits.
  • Your art work will determine your board size.
  • Your board size determines your Tray size
  • Your tray size determines your Bottle size
  • 4 x 6 board fits a 5 x 7 tray and 1 pint bottles for developer and etchant
  • Two plastic photo tongs in different colors
  • A measuring beaker with half ounce markings
  • Above found at a Photo shop. Trays, Beakers, Bottles and tongs
  • Plastic tablecloth to protect your counter
  • Plastic gloves
  • Timer

Never mix the trays, tongs or bottles. These are dangerous chemicals.

Mix your developer as directed and place in a bottle marked as developer.

Mix your etchant as directed and place in a bottle marked etchant.

Ferric Chloride is usually pre-mixed in a bottle and it is dark brown. You must lift the board out of the etchant to inspect it. Ammonium Persulphate is a white crystalline powder you slowly mix into the water until it dissolves and then put it into the bottle marked etchant. It is a clear light blue liquid and you just watch the board as it etches.

Note: The pre-sensitized boards are sensitive to heat as well as light. Keep them in a cool dark place until ready to be exposed. Make sure you have time to complete development after you expose your board. Waiting may cause the resist to change.

Step 2 Exposing the board

If this is for a double sided board. You can take the protective film off both sides of the board and tape the top and bottom art work onto the board. Put a tight tinfoil box on the bottom. Block all light. Edges Too. Expose the top and then protect it and then expose the bottom.

  • Once your art work is ready Close the blinds and cover up direct light.
  • Get your timer set for the exposer time or the side exposer time.
  • Put your developer in its tray
  • Remove the protective film on the resist side of the board
  • Place your art work onto the resist side of the board. Make sure it is oriented correctly. You can read the writing on the board.
  • Put your board into the art frame.
  • I use two pieces of class and photo clips as my art frame.
  • You need to keep the art work tight against the board to get a good image.
  • Place your art frame under the exposer frame a little in front of the frame.
  • Mark the front edge if you need to turn the board
  • Turn on the exposer light and start the timer. Put the art frame in the sun.
  • 10 minutes for small boards and your side is done
  • 8 – 10 minutes a side for bigger boards
  • Noon time sunlight is about 6 - 10 minutes and your side is done
  • My 4x6 board was 9 minutes each side. Rotated once.
  • With good art work it is difficult to over expose your board
  • When the time for a side is up rotate your art frame to the next side
  • When the exposer time is over turn off the light or get out of the sun
  • Remove your board from the art frame
  • Protect your board from too much light
  • Now is good time to put on your gloves

Step 3 Development

  • Put your etchant into its tray and into a bigger tray with about a half inch of hot water in it. I use my 13x9 baking dish.
  • Remove the art work from your board
  • Place your board resist side up into the developer
  • Start an up counter on your timer
  • With fresh developer you should see the art work in two minutes
  • Keep agitating the tray
  • I rub the board with my gloved fingers. You can use a sponge too
  • Wait until all of the copper is shiny. About five minutes
  • All of the little holes need to be shiny too
  • If it is a double sided board keep flipping it over to check your progress
  • It is difficult to over develop your board
  • The time will increase after each board. The developer gets darker
  • If everything is good then rinse your board under warm water. This fixes the resist so it is not sensitive to light or the developer anymore.
  • Open the blinds and turn on the lights
  • Pour the developer back into its bottle

Step 4 Fixing errors or making modifications

  • Using a paper towel wrapped toothpick and 91% Isopropyl Alcohol to clean out errors in the resist. Just dampen the corner with the alcohol. You do not want to mess up other areas of the resist.
  • Add modifications. They have resist pens and art work

Step 5 Etching

  • It helps to warm up your etchant
  • Place your board into the etchant copper side up
  • Start an up counter on your timer
  • Keep agitating the tray
  • If it is a double sided board keep flipping it over to check your progress
  • Change the hot water every fifteen minutes or so
  • It can take an hour or more to etch a board
  • Once the etching starts it can move very fast. Check your board every 15 for the first half hour. Then every 10 minutes to the end. You can over etch your board
  • When you are done etching rinse your board thoroughly
  • Pour your etchant back into its bottle
  • Rinse your trays out
  • Rinse your tongs and everything else.

Step6

  • Cutting up your board Dremel circular saws are big enough to keep a straight line easily
  • Dremel has a circular saw adapter. I found it difficult to use. The blade kept binding in the PCB.
  • Any fine saw will do
  • Metal shears work too

My fix for Double Sided boards is using thin wire like wire wrap wire. Drill your holes bigger about .039 or big enough to fit your lead easily. Put the thin wire into the hole and carefully solder it to the top trace. Try not to get solder into the hole. Push a lead through the hole to flatten the wire to the sides of the hole. For more current use up to four wires.

 

 

 

Working with Fitzing.com. You need Electronics knowledge and Desk Top Publishing experience. An example is the Object Label used in all views. Right click the Object select show label. Select the Object and Left click the Label and drag it. Right click the Label select edit, size, rotation and Display Details.

You must get the BreadBoard and the Schematic Perfect before you can get a good PCB. No Birdcage Wires anywhere. Test all circuit paths by clicking on a node. Then in the PCB remove any Birdcage wires, rotate and move the parts and delete and make new circuit paths. You make big changes in the BreadBoard first then the Schematic if you need it and then the PCB.

In the PCB deleting a trace is Deleting a wire in the BreadBoard and the Schematic. Complete your changes in the PCB and check for birdcage wires in the other views. Make wires out of the correct connections and delete the rest. The default PCB is double sided. Auto-routing is automatic in the other views as you add parts and wires. Start moving, orienting and wiring each part on your PCB as you add them.

Making multiple circuits on one PCB. Save your project as somethingA10. In PCB view click the PCB and in the Parts menu set Sticky to unchecked. Click and drag the PCB away from your circuit. Set your PCB to the size that you need. 4x6 is width 101.6 and Height is 152.4mm. Position your circuit to the left of the PCB and close to where the duplicate will go. Drag a selection box around your circuit. Let go. In the edit menu select Duplicate(Ctl-d). Wait for it to show up. Do not click it. Use the arrow keys to move your duplicate onto your PCB. Repeat this for each copy. The BreadBoard and Schematic will be a mess. Line things up nicely. Save your project. Make an editable PDF. Wait for it. Done.

I do not put Sticky back on. Watch out for Duplicate errors. All of the part labels have copy numbers in them. Do not touch the BreadBoard or the Schematic. To fix errors delete the bad circuit and make a new duplicate circuit. The more parts in the circuit the longer it will take to make a duplicate.

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Over here I use Kinsten presensitised boards with their DP50 developer (Sodium Metasilicate). I also use a Kalex UV box that contains 4 UV tubes.

Exposure time is 90 seconds, developing in cold water, another minute or so. I use LabTimer on the iPad.

I also use ammonium persulphate but my etch times are around 10-15 minutes using 5:1 water:etchant in a Kinsten etching tank with air pump. Like you said, the water needs to be hot, but after destroying a couple of aquarium heaters (they really sizzle when the glass is broken), the last couple of batches I have made with hot water from the microwave. Not sure of the temperature, maybe 60-70 degrees C. Maybe.

Cutting up the board, I just use a hacksaw and then belt sander to take it down to size. On my last etch I also worked the corners so they are nice and round.

Fritzing is a neat program, but I find its autotracing a little ugly, and prefer CorelDraw. I guess it's just personal preference but I like to keep all my traces snapped to multiples of 45 degrees and avoid 90 degree bends when I can. The schematic view in Fritzing is a great improvement over pencil and paper.

For labeling I have just tried using clear plastic adhesive sheets. I design the labels on a copy of the PCB layout and print them off, cut them out and carefully stick them in place. The finished board looks pretty good. I understand there's photosensitive screen printing sheets so I might have a go at locating some, though I may have to get them direct from the US.

Re: soldering vias: Why not just use PCB header pins? Poke through, solder on each side, snip off. What is the advantage with using multiple individual wires?

Tim

Curious.  Being new to the whole Robot thing.  How many amps and voltage can the cards handle?  Is it more for the Arduino 5v or can I use it for a larger project.  

Somewhere about 3 - 5 amps. You can make thicker traces if you need to.