Introduction: Intro - Creating a PCB Board for the Moteino (design, Etching, and Soldering)
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The purpose of this tutorial is to create a PCB board for the Moteino. John and I will use these boards for testing our iteration of openHAB along with Mosquitto.
This is my first go at creating a PCB board from scratch. I'm not saying this is the best or correct way to do this; however, it works and I've found that I get consistent results using this process.
- EasyEDA account
- One-Side Copper Clad Single PCB Printed Circuit Kit Boards 70x100x1.2mm
- Muriatic Acid (Hydrochloric acid)
- Hydrogen Peroxide
- Cardstock paper
- Sheets Heat Toner Transfer Paper For DIY PCB Electronic Prototype
- Laminator (a clothes iron may be substituted)
- 1/16" Drill Bit for the headers
- 7/64" Drill Bit for the barrel connector
- LT1084CT 3.3 LOW DROPOUT POSITIVE VOLTAGE REGULATOR
Hydrochloric acid is a colorless liquid with a sharp and extremely irritating odor. Upon exposure to air, there is an immediate release of toxic hydrogen chloride gas. As a strong corrosive acid, hydrochloric acid reacts with many metals producing flammable hydrogen gas that can become an explosion hazard. Because of the potential to release toxic vapors, hydrochloric acid should never be opened, mixed, or transferred to other containers at any time while inside a vehicle or in any other small enclosure without a mechanism to vent all fumes to the outside.
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Step 1: PBC Design With EasyEDA
EasyEDA is a free, zero-install, Web and Cloud-based EDA tool suite, integrating powerful schematic capture, mixed-mode circuit simulator and PCB layout in a seamless cross-platform browser environment, for electronic engineers, educators, students and hobbyists.
Step 1 - Use Design manager to set Canvas, Grid, and Other
- Units = mm
- Grid Size = 2.54mm
- Routing Width = 0.9mm
Step 2 - Create a Board Outline
Before placing footprint we need to create a board outline. The board outline must be drawn on the BoardOutLine layer. So first, set BoardOutLine as the active layer, then draw the board outline using Track and Arc from the PCB Tools palette. Start at 0,0 coordinates and draw a 70 x 100 mm rectangle
Step 3 - Create Copper Area
Set Top Layer as the active layer, then draw the copper area outline using the Copper Area from the PCB Tools palette. Start at 0,0 coordinates and draw a 70 x 100 mm rectangle
Step 4 - Start drawing the board as you wish.
You may download my version (attached) and watch the video as a reference. This is the 4th or 5th time for me to use this program. So bear with me and my learning curve as I recorded this video.
Step 2: Print Your Design for Toner Transfer
Step 1 - Prepare the transfer paper
Cut the transfer paper in half in order to maximize use of each sheet. Tape the transfer paper to cardstock. Be sure to tape all the way across the edge of the transfer paper that goes into the printer first. You do not want to jam the printer and waste your paper.
Step 2 - Export your schematic
Click the folder icon -> export -> select "pdf" -> Merged layer -> select Export by "TopLayer" (don't mirror) - select "Black on White Background" for Colour -> click export.
Step 3 - Working with the PDF
Now you have a pdf to work with. I've moved the object to another full (letter size) page and created a copy. This allows me to print out 2 copies at once. You do not have to do 2 copies. Print out a test copy onto plain paper. DO NOT SCALE OR RESIZE. Be sure to print as is. The pins will not line up with the print out if you alter the size of the image.
Step 4 - Check to make sure the pins and transfer paper line up with the test page
Look at the test page and place your board on the pin holes to ensure a match. Flip the paper over to make sure that the pin out matches your board. In this case the copper will be on the bottom of the board facing away from the Moteino. This is why I flip the paper over to make sure that the VIN and GND (pinouts) match with my plans.
Step 5 - Print onto the transfer paper (attached to the cardstock) 3 times
It may take some practice to line up the paper into the printer each time. If you are off, the images will not match up and ruin the transfer paper. You may can get away with printing twice, but I have found better results with 3. I've never been able to get a good transfer is a 1 time print.
Step 6 - Cut the transfer paper to match the board
You only need to cut the edge of the paper that matches the straight edge of the board. The transfer paper can overlap the rest of the board.
Step 7 - Clean the Board
Use steel wool and acetone to clean off oxidation. Be sure to use gloves to keep oils from your skin from contacting the board. Pay special attention to the corners of the board as they are commonly missed. You can wipe them by starting in the middle of the board and pulling the steel wool across to each edge. Finish off with rubbing alcohol to ensure a clean surface. I use cheap $1 spray bottles to keep control of how much of each (acetone and alcohol) is used.
Step 8 - Use the laminator to transfer the toner (a clothing iron may be substituted)
Use the laminate sheet to line up the board and the transfer paper. Be sure to hold the paper tight to the board when placing into the laminator as to keep both the edges lined up. Make 4 passes through the lamintor while rotating the board and transfer paper 1/4 turns each pass. Give the board time to cool before removing the transfer paper backing.
Step 9 - Touch up missing areas
Some of the board may be missing toner. Use nail polish and a permanent marker to coat these areas. Don't press hard with the permanent marker because it will chip off the toner.
Step 3: Acid Etch the Board
Step 1 - Prepare the Work Station
Make sure you are in a well vented area. This etching solution will put out quite a bit a fumes. I'm using cardboard to control the air flow underneath a microwave vent fan. In my case, the vent is exhausted outside. CAUTION! Not all range vents go outside. I'm placing the etching solution in a glass bowl with a flat bottom. The PDB will fit directly into the bowl and can be covered with 4 oz of liquid. Place cardboard anywhere you believe the solution can spill. This solution will ruin any finished surface including your counter tops, oven, range, sink, and on and on.
Step 2 - Place the Board into the Etching Solution
I'm using 2 parts (2 oz) Hydrogen Peroxide and 2 parts (2 oz) Muriatic acid. Where safety gloves and goggles to protect your skin and eyes. Be sure to open the muriatic acid away from your face and body. This stuff will emit vapors as soon as you take off the cap. Drop the PCB into the solution making sure that you do not splash the liquid out of the bowl. Leave the board in solution until all of the copper has dissolved. The solution will turn a green color as the copper becomes part of the liquid solution.
Step 3 - Rinse the Board
You can keep the solution if you wish. I choose to dispose of the solution while rinsing the board off. Once all the copper has dissolved, you can rinse off the board. I prepare to do this by filling my sink full of water in order to dilute the solution. I transfer the bowl (with the solution and board) to the sink and place it into the water with running water and pull the drain. Be sure not to plash the solution anywhere but into the water. You do not want to ruin your sink. Rinse the board, bowl, and sink thoroughly
You can clean the remaining toner and nail polish off with acetone and steel wool. Do a final wipe with alcohol. Finally, I use tin snips to cut the board into two separate parts.
Step 4: Drill and Solder
Step 1 - Drill the holes
Take your time with this step. You have come too far to screw up the board by getting into a hurry. I'm using a 1/16" drill bit for the header holes and 7/64" drill bit for the barrel connector holes. Place the board onto a piece of wood that you are willing to drill into. I find the header rings do a good job holding the drill bit in place as I use a hand drill. This will work better with a drill press.
Step 2 - Solder
I soldered the headers first. Because these holes are larger than normal, soldering is more difficult than usual. The solder will only bind the header pin to the copper. You want get any progress trying to solder to the board material by itself.
Step 3 - Test for Electric Shorts
Make sure that there are no electric shorts before plugging your Motieno onto the board. I use an Ohm meter and check every circuit against the ground.
Step 5: That's It! You Are Finished.
You should now have a functional test board. I look forward to programing this thing soon. Rest assured that I'll share my experience.
I've updated the layout of the board for Easy EDA for your import into your account.