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| Collection #1 of home-made circuit boards |
| Boards from Left to Right and Top to Bottom: Solar Power Center V2, SPC3, Low Voltage Disconnect, SPC2, Dark Activated Switch, Pulse Width Modulator, Solar Charge Controller, Same. |
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| Collection #2 of home-made circuit boards |
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| Battery Voltage Monitor BVM1 prototype |
| Boards from Left to Right and Top to Bottom: Lightning Detector, Musical Beat Detector, Sine Wave Code Practice Oscillator, Differential Temperature Controller, Same, Stereo Mic Amp, Solid State Relay, Switch-mode converter, SSR, Dark-on Lamp, Low Voltage Beeper, PWM, PWM, Low Voltage Disconnect, Switch-mode converter. |
This article describes one method of making printed circuit boards at home using a laser printer and Press-n-peel transfer film. The process shown here can be used to make single-sided printed circuit boards, a double-sided circuit board can be simulated by manually adding the top-side wiring with point-to-point wiring on the bottom of the board. Printing top-side traces on a two-layer board is possible, but alignment of the two layers is difficult and the holes (vias) will not be plated through. Printing just the solder side traces is the recommended process. When laying out the circuit board in a CAD program, it works best if you make most of the connections on the bottom side and keep the top side connections to a minimum.
All of the circuit boards shown here use the older through-hole technology. It is possible to route one trace between standard 0.1 inch pads. Multiple traces between 0.1 inch pads are not recommended due to the resolution limits of this process. Boards using surface mounted technology (SMT) may also be produced, but only the larger parts such as SOT-23, SO-8, SO-14 and similar are recommended since parts with finer lead spacing are beyond the resolution limits.
The home-made circuit boards are well-suited for making one-off projects. They are also very useful for building prototypes in order to debug circuits and parts layouts before having commercially made circuit boards manufactured. With the use of these prototypes, it is possible to have a nearly 100% success rate when final designs are sent to a PCB fabrication company. Many of the boards shown here were used for projects on this site and a number of them were eventually turned into commercial kits with manufactured boards.
Many of the circuits shown have been initially designed by first building them on a plug-in prototype board. Some of the simpler circuits have also been started by soldering parts on top of blank copper-plated circuit board material using the dead bug prototyping method. Other circuits have been initially built using point-to-point wiring on perforated circuit boards. While making hand-wired prototyes is an optional step, doing so can help with the first level of circuit verification and debugging.
Once the circuit operation has been verified, it can be transferred to a printed circuit design. There are many PCB cad programs available for different computing platforms. Your author has used Autodesk Eagle for the majority of these designs. KiCAD is a free and open-source PCB layout package that has matured to the point of having all of the features of commercial PCB software.
This is a lengthy and multi-step process. There is a real economy of scale in making more than one board at a time, two boards is a good place to start. They can be two of the same boards or two different boards as shown below.
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| Bottom side artwork, LED sequencer and differential temperature controller |
Print the black and white bottom copper artwork on a blank piece of paper with a laser printer. Do not attempt to use an ink jet printer, it won't work for this process. Cut out a piece of Press-n-peel film that is approximately 1/4" to 1/2" wider and longer than the printed artwork. To make a good cut, use a metal square and scratch a thin line on the rough side of the film, then cut along the line with scissors. Be sure to clean your hands before working with the film, oily residues can prevent the resist layer from sticking to the copper.
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| Printing Press-n-peel |
Using two small pieces of Scotch tape, tape the leading-edge corners of the blank press-n-peel film to the pre-printed artwork page, rough side up. Make sure that the tape does not cover any of the PC artwork and the film is flat on the paper. Be sure to press the tape firmly to the film and paper so that it does not come off and gum up your printer. Re-print the artwork onto the paper with the film using the printer's hand-feed tray.
Prepare the blank circuit board for etching. Cut the board to size, I place the board in a vise with a piece of thin protective cardboard on the copper side then use a hack-saw to make the cuts. File the edges and corners of the board smooth and use a square to make sure the board is rectangular. Make sure the copper edges of the board are smooth to the touch.
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| Cleaning the blank PCB |
Clean the copper side of the board with fine steel wool and a few drops of liquid laundry detergent. Use a green dishwashing scrubbie to polish the surface of the copper so that it is bright and even. Dry the board with a paper towel and avoid getting any fingerprints on the copper. Try to minimize the time between cleaning the board, ironing on the resist film and etching to prevent oxidation of the copper.
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| Printed Press-n-peel film and blank PCBs |
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| Ironing the resist layer to the PCBs |
Carefully lay the press-n-peel material rough side down on the blank PC board, all surfaces should be free of dust. Make sure the image on the film is parallel to the board edges. Iron the printed press-n-peel at a medium-high temperature for about 5 minutes using a circular motion. Be sure to iron the edges and corners of the board, they take longer to heat up than the center. It can be helpful to lift up a corner of the press-n-peel to see if the transfer layer is sticking to the PCB copper. Note that the transfer ironing is the most critical part of the board making process.
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| Removing the Press-n-peel film |
Once the resist layer has been successfully ironed onto the board, take the hot board and run cold water over it while gently pulling the transfer plastic off.
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| Removing excess resist from holes and between traces |
Use scotch tape to clear the excess transfer from the printed holes and between circuit traces. It is a good idea to de-sticky the tape first by putting the tape on your fingers, this will prevent it from ripping up the desired resist layer. Compare the cleaned board to the paper artwork to make sure all of the holes and traces are clear. An X-acto knife with a sharp tip can be used to scrape off any excess resist material.
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| Clearing between the traces and patching holes |
Using Press-n-peel on a copper board is an imperfect process, there are a few tricks to make the board come out better. Use an indelible ink sharpie pen to fill in any undesired holes in the resist layer, be sure to lay the ink down thick. Small pieces of scotch tape can also be used to cover larger holes where the resist layer did not stick properly. If the board layout has copper around the outside edges, it can be helpful to put scotch tape around the edges of the board, wrap the tape around both sides of the board.
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| Preparing the PCBs for etching |
Use rubber gloves while working with etchant, it can cause burns and stains. It is also a good idea to wear a respirator mask while working with etchant. This process should be done in a well-ventilated area such as a garage. It can be helpful to put the etching tray inside of a larger plastic tray to capture any spillage.
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| Etching the PCBs |
Place the board, copper side up, in a plastic tray of FeCl or simiilar etching fluid. Make sure there are no air bubbles on top of the board, especially around small circular pads. Place a heat lamp a few inches above the board so that the etchant becomes warm. Constantly rock the tray around with a circular motion so that fresh etchant circulates over the copper surfaces.
Etching with warm FeCl takes around 15 to 20 minutes, the larger etched areas will become visible first. You can lift the edge of the board with a plastic tool for inspection. When you can see that all of the copper has been fully etched, remove the board from the etchant using plastic tweezers and rinse it off with warm water. Remove any residual tape from the board edges while rinsing. Do not leave the board in the etchant too long or it will get under the edges of the traces. Pour the excess etchant into a plastic container, it can be used several times if you add a small amount of fresh etchant to the used etchant.
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| PCBs after etching |
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| PCBs with resist and tape removed |
Clean the resist layer off of the board using a solvent such as Goof-Off, mineral spirits or paint remover. Use rubber gloves to protect your hands. Use a paper towel to soak up any liquified residue and repeat the process until all of the residue is gone. Clean any remaining residue off of the board with a small amount of liquid laundry detergent and a dishwashing scrubbie. The edges of the board can be filed again if you want to correct any alignment issues or remove excess edge material.
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| Drilling the PCB holes |
Drill the holes in the board using a drill press and small PCB drill bits. Larger holes can be pre-drilled with a small drill bit to center the hole before moving to a larger drill bit. Be sure to drill carefully so that the holes are straight in line for parts such as DIP ICs. Test-fit all of the larger parts to make sure the holes are in the right positions. Off-centered holes can be adjusted with a fine-tipped jeweler's rat tail file or by using a slightly larger drill bit.
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| Top side of two finished boards |
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| Bottom side of two boards with added top-level traces |
This is a good time to use the continuity function of a DVM to beep out the PCB to find and repair any shorts between adjacent traces. It is a lot easier to do this before soldering any components to the board.
Solder the various components into the board. IC sockets are recommended for parts with DIP packages, they can insure that the pins line up with the socket and can be handy if you need to remove ICs to debug any wiring problems. If your board has top-level traces, manually wire them on the bottom of the board. Your author likes to use tinned copper hook-up wire and thin teflon insulation for the top-level wiring. Teflon does not melt while working with the wires. Make small J-shaped hooks on the ends of the wire so they are secure around the component pins. If you don't have teflon insulation, regular hook-up wire or wire-wrap wire can also be used.
Connect the board to whatever power supply you will be using and verify its operation. If you have a current-limiting power supply, that can be used to verify that there are not short circuits before applying full power to the board. A series resistor with a non current-limited power supply can also be used for the first test. Once you are satisfied that the board does not have any shorts, proceed with any further testing you may want to do. If you do find any errors in the board, it is possible to cut bad traces with an X-acto knife and rewire the mistakes with hand-wiring.
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