Making a PCB By Hand

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Steps:

  1. Cut the copper clad pcb board to size, and sand the edges (220 grit can be used for the edge).
  2. Prepare the PCB surfaces by sanding with 3000 grit sand paper. The main purpose of this is to remove oxidation. Keep sanding until you the surface is no longer shiny, but is a matte color (possibly the base). Within 1 week the copper will have oxidized, and will need to be sanded again. You may want to wear gloves..
  3. Wash the sanded PCBs with soap and water. With clean hands – clean the surface of the PCB with a non-linting paper towel and 91% isopropyl alcohol.
  4. Prepare two transparencies – one on top of the other to optimize for opacity. If you only use one layer – the UV light will get through the black ink – so double up!
  5. Take great care to align the transparencies on top of each other (strongly recommend you use a magnifying glass). Tac (or vulcanize) the two transparency sheets exactly on top each other by going around the edges with a heated soldering iron. Do this then for the other side of the PCB board. THEN tack these two layer on top and bottom only – leave the sides open so that the sheets form a sleeve you can slide the PCB into later on.
  6. Cut the negative photoresist to be a bit larger than the PCB.
  7. Use tape to grab the bottom removeable layer of the PCB, and peal it off. Carefully apply the sticky side to the PCB. Do small steps with your fingers, from the middle to the side – and avoid bubbles this way (being careful). Bubbles will cause the copper to be etched where it shouldn’t be. Don’t be in a hurry for this.
  8. Use a box cutter to clean up the excess photoresist around the PCB.
  9. Using small circular movements – and always moving – use a hot air gun to better adhere the photoresist to the board. Do this for about 1 minute per side or less. We used 110 deg C and a medium air flow.
  • Insert the PCB into the transparency masking tool.
  • Place the sleeve+PCB into an acrylic rig with clamps.. We don’t want any space between the mask and the photosensitive material – if you have any gap at all – your edges will blur and your traces will not be crisp.
  • Put the clamped PCB under a UV lamp for 5-7 minutes per side.
  • Using 99% Pure soda ash powered – add water in a 1:50 powder to water ratio to generate liquid 2%-5% Soda Ash solution (this doesn’t need to be exact).
  1. Remove the ‘second’ side of the PCB film from both sides of the PCB.
  • Soak the developed PCB in a soda ash bath.
  • Using gentle strokes of a paint brush – remove excess unexposed PCB. Flip the board in the bath – and stroke the other side as well.
  1. Rinse the board in a large amount of water. If you have to, brush and clean the surface. Look for damage to your traces before proceeding.
  2. Put a clamp or tape onto the board
  • Put into a heated tank of Ferric Chloride – Turn off heater 2-3 degrees before it reaches 55 degrees C. 415 Ferric Chloride – in an etching – with a thermonitor and heater – and a fish tank pump. Get the etching solution up to 50 degrees C. We decided to turn off the pump at 45 degrees C and monitor the temp to make sure it actually hits the 50C – however we kept the circulating fish pump on. Once done and cooled, you can reuse the Ferric Chloride Solution again in the future.
  • Etch for 1.5 to 2 minutes. Ideally the board is diagonal and bubbles are coming up over the solution
  • Remove the board and rinse in water.

Notes

 

Event #2

Steps:

  1. Fill a bath with Sodium Hydroxide power – 2-5% in water (this will be used to dissolve the blue photoresist film). Take great care, this is a strong base – and will injure your skin. Also don’t breathe the vapor that comes off when you add the powder to water. Note that the water bath and container will get very hot – be sure it won’t melt the container.
  2. Use tweezers and carefully insert the board into the strong basic solution. After a minute or two use the sharp tip tweezer to peal the photoresist off of the copper trace. Eventually the whole photoresist will dissolve.
  3. When all the blue photoresistant film is removed – run the board under tap water for a while, so that you can handle it by hand.
  4. Hold the board up to a bright light to inspect carefully where the bridges are – these will be hard to find so look carefully.
  5. Take a box cutter and cut away at the bad traces.­­­ Be very careful with this to not accidentally cut a useful trace.
  6. Use a multimeter to test continuity. We used a multimeter in continuity mode – with a beep feature to make things easy. Be sure to check each pad against other pads to make sure no traces are comingled.
  7. Clean debris and grease with rubbing alcohol and a paper towel.
  8. If you have a broken trace that you need to fix – use Kapton tape to mask out surrounding traces. Place a wire where the broken trace should go, and solder it down using a fine tip solder iron. Remove the Kapton tape. Take a file and file down the new solder wire so that it is essentially level with the PCB – finish this off with some sanding paper. When sanding and filing – use tape along the edges to mask out good traces. Use your finger to feel that the wire trace is more or less level with the trace.
  9. Put the board on a paper towel. Add a solder mask – (the green stuff on PCB board) – as a paste as a single line in the center. Put a transparency film on top and take a straight edge and smear the paste carefully from the center to the sides in squeegee motions.
  • Apply a downward even pressure on the transparency – make sure there are no bubbles.
  • PREVIOUSLY – create a transparency envelop for the board using the masking layer for pads – as described before.
  • Carefully place the transparency + board inside the envelope and clamp it into the UV.
  1. Cure the solder mask under UV light for 20 minutes per side.
  • Peel off the transparencies. Peel off these transparencies carefully so that the tips don’t pick up.
  • Use rubbing alcohol and rub off the masked-out portion (these should be the pads of your board, where surface mount components will connect). The transparency paper can be thrown away. Some pressure might be needed when rubbing – but try low pressure first.
  • Apply liquid tin with paintbrush to the pads. They immediately turn silver – this prevents copper from oxidizing, and is easier to solder to. This has a bad smell and is hazardous. Once done wash the board.

Notes

  • We used green Mechanic UV Solder mask paste
    • An alternative is using a film as a solder mask. Remember to remove the sticky covering, and apply to the PCB. Be sure to avoid bubbles. These steps are very similar to the to the photoresist. Note however that the film will need to ‘bake off’ for about an hour in an oven.
      • Note a piece of tape may be needed to begin to separate the plastic
    • Note that solder mask is thought to be toxic – be sure and use gloves during this portion.
    • If there is ever a trace too hard to fix – consider if it can be mended after the components are added, by using jumper wires and other post-soldering tricks
    • Note, packing tape can be placed on top of the PCB – and can be torn away to peel off the photo resist film.

Event #3

  1. Use a fine tip drill (a drill press) – or see our custom designed drill
    1. This drill tip should be 0.5mm – we use Straight Shank – Twist Drill tips
    2. Use perfect perpendicular up and down motions – it is a good idea to practice on a scrap board.
    3. Place a piece of cardboard under the board for when the tip pierces through
  2. Place vias (drill holes) at each place there is a through pad (this pad should be on either side of the via). We have about 20 of these on our designs. Note, check and count the number of holes – it’s easy to miss a mark on one of your two sides. Drill on the side of the board with the list tolerance for lateral motion.
  3. Take a thin copper wire – and submerge it in liquid tin to prepare it.
  4. Insert the thin wire through each via. Cut the wire using a disposable pair of nail clippers – the length of the via wire should be twice the board – with ½ of the board width on each side sticking out.
  5. Take needle nose pliers and compress each end of the tin wire to make a ‘rivet’ or mushroom shape. Double check you did not miss any.

Notes

  • The custom designed drill is: a 12V DC motor – from a tape. Ideally we want medium speed, high torque. Best would be to have bench drill rig
    • Prepare a drill bit by wrapping a thin copper wire around the base to help it secure a better grip
  • 1 in 5 boards may need more detailed finishing or redo..
  • For compressed acrylic (Plexiglas) – it’s actually preferred to use quartz glass. Not that polycarbonate can be used – but because it absorbs more UV
  • We cut our copper wire using an old disposable pair of nail clippers.
  • If a via pad is not directly below another pad start by drilling through perpendicular – then push the drill to be at an angle to establish a diagonal wire connection. Then recreate this angle for all future pads to compensate for the offset.

Event #4

Steps

  1. If your board has a non-traditional shape – you can cut it to its final form. A Dremel with a diamond wheel can be used to cut the fiberglass. Please wear a mask when doing this because fiberglass is bad to breath in. Make small stroking motions – use small equal pressure to cut through the board – don’t cut through it all at once.
  2. Sand the edges to smooth them out. Wash powder away from the board with water, or if there is finger grease – use rubbing alcohol.
  3. Apply static component with superglue. A small wire can be used to apply glue to small components. We happen to be using a 3 color LED with 4 contacts – 3 cathodes and 1 anode. Be careful with orientation here, all LEDs have an orientation.
    1. A hot air gun with low air flow can be used to accelerate the drying of the superglue.
  4. Using the tinned wire tack each of the small contacts points on the static components. Apply a liquid flux to the contact point, and tack again to ensure a good soldering point. You will want to use an alligator clip, and magnifying glass soldering rig to help you hold components. Place the PCB in a small amount of paper towel before clamping the alligator clip to protect the board.
    1. A really thin wire only needs a small press, almost instant. The smaller the wire, the less time is needed.
  5. Solder the other end of the wires to the contact points on the board. You can use a sharp box cutter to clean up any remaining excess wire.
  6. Encase your static components and wires in a liquid plastic, and dry it quickly with a hot air gun.
  7. Preheating the board using a hot air gun. The hot air gun is at 230 degrees C for us now, but we don’t want the board to get too warm – this is just being warmed up so that future soldering goes better. The actual board temperature should be about a 1/3rd of the melting point.
  8. Use a paint brush and add a thin code of liquid flux before adding the paste.
  9. For each via and pad: preheat the pad again for a few seconds – the remove the air and apply the flux paste ( use a syringe of flux paste (63% tin 27 % lead – a standard)). The remove the tip of the syringe (to prevent it from melting) and apply the hot air to the again. The first hot air ensures the paste adheres to the board (it won’t adhere well to a cold board). The second blast of heat ensures the paste becomes tackier – as it has a tendency to spread out too much.
  • From your reel of LED components, cut just the number of components you need. Set up a work area, just as a little piece of wood or cardboard, and place your components down. You can test the orientation of your LEDs if they are low power – using the “DIODE” mode on a multimeter – if you get the orientation correct – the LED should light up. Also, all components have a fiducial mark indicating their orientation. Understand this orientation, then pick them up with bent nose tweezers.
  • Carefully place the component with the correct orientation on the board. Ensure that each side of the component is on each side of the pad.
  • Use the soldering hot air gun set to 320C, solder the component. Keep the air flow low, and the distance above the board at about 1 cm. What you should see is that everything melts, and becomes shiny. Use a low rate of air flow or your components will move around.
  1. It is possible to place all components first, then solder them all at once. You will see that the component may wiggle into place using the flux and surface adhesion. Note, don’t breath the smoke – it may have lead and other toxins. Work in a well-ventilated space.
  • Use the jewelers lens and double check each of the soldering points.
    1. You can touch up bad soldering points using a soldering iron, and some solder wire. You can apply liquid flux first to the solder point to assist with adhering the metal.
    2. Where possible check your solder points using a multimeter.

Notes

  • Be sure to clean the fiberglass dust carefully, you don’t want this to linger around.
  • We used Flux F5 as our liquid flux.
  • We encased components in plastik-71 a liquid acrylic PCB insulating varnish.
  • Note if you get clog the syringe – you can heat it up again with a

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