PCB Fabrication Procedure

There are a lot of hobbyists that want to design and build their own custom printed circuit boards (PCB's). It will save you money if you're making a lot of different board designs on a small scale. If you need to make 50 copies of something or don't want to spend the time to make your pcb's just order them from a professional pcb manufacturer. This procedure is for people who want to get their hands dirty and learn how to make their own circuit boards for lower cost, faster turnaround, or the simple satisfaction of it.

My method of fabricating pcb's is based on the numerous tutorials and websites that describe the familiar 'Toner Transfer' process. After practicing a few years I've combined parts of each tutorial with some tricks I've learned to make this fabrication procedure. This method is useful for making single boards or panelized board designs. I prefer toner transfer vs. a photolithography based method because the copper clad boards are very inexpensive when purchased in bulk and there is no light sensitive photoresist to worry about. Photolithography is capable of better resolution and smaller feature sizes than toner transfer but it's only a limitation for extremely small features (i.e. <0.005" wires).

Fabrication procedures vary from person to person and these have been customized to reflect what has worked best for me. There are a lot of ways to make a pcb and I will point out some alternatives along the way. Making pcb's is a laborious process and the small tricks that come with practice will make the difference between good boards and coasters. It's normal to have problems when getting started but the good news is that laser toner and copper clad boards are cheap!

Disclaimer

The chemicals and power tools used here can hurt you. Follow appropriate safety precautions and use common sense. You are responsible for your own safety.

Materials

  1. Cadsoft Eagle or other pcb design software
  2. Laser printer - HP printers/toner work well
  3. Toner transfer paper - Releases easily in water and is worth the cost. It's possible to use glossy magazine paper but your results will be less consistent
  4. Copper clad boards - Single or double sided from Electronic Goldmine, MPJA, Ebay, etc. I prefer to buy double sided board in bulk and etch away all unwanted copper
  5. ScotchBrite scouring pads
  6. Green toner reactive foil (TRF) - Applies an impermeable plastic film over porous toner to eliminate pitting and partial etching
  7. HBC H-220 laminator - Although not strictly necessary, this will allow you to make a large number of double sided boards very reliably and consistently. You can also use a clothes iron but it's difficult to evenly heat the surface resulting in patches that don't adhere correctly. A random laminator probably won't work, I tried one from 3M but the toner wouldn't stick
  8. Safety glasses - Protects your eyes from acid and flying debris
  9. Rubber gloves - Protects your hands from acid
  10. Leather work gloves - Copper clad is extremely hot during toner transfer process and it's necessary to handle the board to pass it through the laminator
  11. Hydrochloric Acid HCl (10M) - This is extremely dangerous in concentrated form. Never breathe the fumes! Cap the bottle as soon as possible whenever you need to use this. Always wear goggles and add acid to water to prevent splattering. Using concentrated HCl is the most dangerous part of making circuit boards
  12. Hydrogen Peroxide H2O2 (3%) - This is used as an oxidizer in the etching solution. Common household peroxide (3%) will work but more concentrated peroxide is better if you have access to it (i.e. 30% lab grade)
  13. Polypropylene etch tank - #5 or other acid resistant plastic
  14. Etchant storage bottle - I use a milk jug (#2 HDPE plastic) with a screw cap. Plastic will survive a fall without spilling acid everywhere
  15. Acetone - Organic solvent to clean copper and remove toner
  16. MG Chemicals Liquid Tin - This is the best tin plating solution. Simply immerse your board in the liquid for a few minutes at room temperature and you're done. Dump the liquid back in the bottle when you're finished. I've also used the Tin Plating Solution from MPJA but it doesn't dissolve and isn't as easy to work with since it requires heating
  17. Carbide drill bit assortment - You should use carbide bits because the epoxy fiberglass will dull high speed steel bits. Plenty of bit assortments at drillbitcity.com for drilling through holes
  18. Dremel tool - High speed drill for carbide bits. It's best to get one with a variable speed setting
  19. Dremel drill press - You will need a drill press to avoid breaking the brittle carbide bits
  20. Band saw / hacksaw / metal shears - For cutting circuit board material
  21. Sandpaper - For smoothing cut edges of circuit boards

Design a PCB

You need a circuit design before you can fabricate a PCB.

Finished Eagle layout for ATtiny24/44/84 mini board pcb. This is one of the pcb designs fabricated here

There are plenty of good tutorials online for Eagle. I prefer Eagle since it's widely used by hobbyists and professionals but there are alternatives like Kicad. This design can be used for fabricating your own pcb's as well as for professional board orders. If you have a number of designs you would like to fabricate simply make a blank board file (.brd) in Eagle (or an image editor) and paste the individual layouts together to make a panel. I typically make panels to fit the copper clad size that's available so the entire board is used. Fabricating pcb panels is a high throughput method that produces a lot of boards efficiently and inexpensively. Having multiple copies of a new design allows you to choose the best board and keep the others for spares in case you need a quick copy later.

Prepare Etching Solution (HCl/H2O2)

The etching solution I prefer is a mixture of 1 part hydrochloric acid (HCl 10M, 30%) added to 2 parts hydrogen peroxide (H2O2, 3%). Do not work with these chemicals without safety goggles, the acid will damage your skin and especially your eyes. It's very important that you slowly add the acid to the peroxide, not the opposite as mixing acid and water is an exothermic process (it gives off heat). Slowly pour the acid into the peroxide/water solution to prevent the acid from boiling/splattering. If you start a solution with concentrated H2O2 (30%) just dilute it with water down to the normal concentration (3%) so the acid is sufficiently dilute. Future additions of peroxide to maintain the solution can be any concentration. You can start the solution by adding in some bare copper wire if you won't be using it immediately. This etching solution is superior to ferric chloride because it's cheap and easy to make and maintain, is reusable, doesn't degrade with time, and the etching capacity actually grows with the amount of dissolved copper. It's also clear so you can easily observe the etching process through the solution with a visual color change to indicate when the solution is losing capacity and requires some maintenance. Since you won't be disposing of your solution, you can make a large volume (i.e. a gallon) and suspend your boards in an etch tank. This allows both sides to etch at the same rate and also allows for stirring the solution.

Maintain Etching Solution (HCl/H2O2)

After the solution begins to etch copper, you will have Cu(II) ions which make the solution an emerald green color.

Emerald green color of HCl/H2O2 copper etchant. This was a previous etch tank design - illustrates solution heating using "double boiler" method with hot water in a sink. Do NOT get this etching solution on your metal sink

The dissolved Cu(II) ions will oxidize copper metal to produce two Cu(I) ions which are soluble, i.e. it dissolves away from the metal surface. The net ionic equation looks like: Cu(II) + Cu --> 2Cu(I). As you use up the green Cu(II) ions and produce Cu(I) ions, the solution will turn a muddy brown color. This makes it obvious when the solution etch rate is slowing down. When the solution is completely brown you need to add some peroxide to quickly reoxidize the Cu(I) back to Cu(II) for more etching. You can also wait for the solution to reoxidize from atmospheric oxygen but this is incredibly slow. If more peroxide doesn't re-green your solution you may need to add more hydrochloric acid. This is the only maintenance your solution will need. This etching solution can be stored in a #2 HDPE plastic container (same as the acid bottle) like a milk jug with a screw on cap. Clearly label your storage container with something like HCl/H2O2 1:2 copper etching solution. You will want to leave some empty space in the container, as you use the solution and add more peroxide (mostly water) the volume of your solution will grow. If it gets too large you need to evaporate some water out by leaving the lid off. It's not useful to add a huge excess of peroxide as it's unstable and will decompose with time. Peroxide is only useful to immediately oxidize the Cu(I) ions. When your solution turns green stop adding peroxide. This maintenance will get less frequent as the Cu(II) ion concentration increases in your solution.

Prepare Copper Clad

Bare copper clad boards will be covered with dirt, oil, and oxidized copper. For best results start by cleaning the surface with some acetone and a paper towel to remove oil and dirt.

Copper clad board after initial acetone cleaning

Use a ScotchBrite pad to lightly scour the surface and clean away the oxide layer. For best results, make strokes along the length of the board in a straight line (not circles). Scratches in a straight line make a nicer finish on the final pcb. Clean the board again with acetone to remove fine copper particles and to prepare the board for toner transfer.

Copper clad board after ScotchBrite scouring and final acetone cleaning - ready for toner transfer

Toner Transfer

This is the most critical part of fabricating a pcb. If the printer doesn't make a perfect replica or if the toner transfer doesn't work properly the finished pcb will end up with defects. Start by printing your circuit design on the toner transfer paper. I've also used glossy magazine paper successfully but it's a lot more difficult to remove later. The trick to the paper is that you don't want the toner to get down into the paper fibers as this will prevent the toner from transferring. In Eagle, choose the Display command and clear all visible layers by clicking 'None'. Then highlight the layers that you actually want to print, i.e. top/bottom, pads, vias, and whatever layer you put the board outline on (useful for alignment on double layer boards). If you want to eliminate unnecessary pads/vias on a given layer simply delete the parts that won't have solder connections on that layer. This makes the final board look a lot neater since you won't be through plating the holes to connect the top and bottom. I typically print the design on standard paper and use some tape along the top edge to hold down a piece of toner transfer paper over the design. Run the same piece of paper through your printer again (use the manual feed tray) and the design will neatly cover the toner transfer paper. If you're making double sided boards you will need two different printouts (don't forget to mirror the top layer so it transfers correctly).

Board layout printed on standard paper

Board layout printed on toner transfer paper

Double sided boards are more difficult because the two layers have to be aligned correctly or components and holes won't match. Align them by trimming 3 sides of the paper as close as possible to the board outline and then line up the trimmed edges.

Trimmed transfer paper ready for assembly and alignment

Tape the top edge (with excess paper) together and check the alignment by shining light through the sheets. You can also do the alignment by putting them together against a light source (window or flashlight) to position the layers relative to each other but I've found that this method is more prone to misalignment errors.

Checking top/bottom alignment with transmitted light

Insert your board between the two sheets to make a pcb sandwich.

Assembled copper clad board between aligned top/bottom layers of toner transfer paper

Run this sandwich through the laminator 6 times, flipping the board and moving horizontally across the laminator opening. You want the applied heat to be as even as possible across the entire board. The laminator isn't going to accept your 1/16" board with two thick sheets of paper without a fight. I found it necessary to wear leather gloves and apply constant pushing and pulling force to the board so the laminator is able to pull it through. Just be extra careful not to shift the paper around or all of your circuit features will move along with it.

Removing pcb sandwich from the laminator

Since it's usually necessary to push and pull a double sided board through the laminator you will want it to be at least 4-5" on one side so there's always part of it exposed. If you are using a clothes iron, lay the board on a flat surface and apply firm downward pressure with the iron on high heat. Don't slide the iron back and forth as it will smear the melted toner. Lift the iron and carefully push straight down again. Make sure the entire surface is evenly heated and pressed for 3-5 minutes. Your results with an iron will vary and it will take some practice to get this right. Either way, when you're finished with this step you will have a boiling hot circuit board with the toner firmly adhered. Quickly run cold water over both sides of the board to solidify the toner before it has a chance to shift around. After 1-2 minutes under cold water, remove the toner transfer paper by carefully peeling it back. You should see the pattern clearly visible on your copper clad with no remaining black toner on the paper. The toner should not come off with light rubbing.

Removing toner transfer paper - success!

If you used glossy magazine paper, this step will take a bit of scrubbing with your thumbs or a toothbrush to remove all of the paper so the etchant can get to the copper. Small defects can be repaired with a sharpie marker as the ink is a decent etch resist. Use a razor blade to scrape away any unwanted toner (ex. the board outline). Rinse the finished board with water and dry.

Toner transfer complete - board ready for Green TRF or etching

Apply Green Toner Reactive Foil (TRF), Optional

Although you can use the toner directly as an etch resist, you will get better results by first covering the toner with an impermeable layer of plastic (green TRF). This "foil" (plastic) will completely eliminate pitting and partial etching through the relatively porous toner. It will help you make very small features that may normally get etched through or over etched with toner alone. Cut a piece of the foil long enough to cover all the toner.

Cut Green TRF material large enough to wrap around both sides of the board and cover all toner

If you have a single sided board keep some extra foil to fold over the front of the board. This is important because if there isn't extra foil over the front the laminator may decide to eat your foil sheet. It's unpleasant to rip the hot laminator apart and retrieve this foil sheet. After running the board through the laminator 3 times, allow it to cool for a few minutes and then slowly peel off the green TRF.

Peeling Green TRF off board to reveal impermeable green etch resist

Unsurprisingly the film reacts (sticks to) the toner and not the copper, so you end up with an impermeable green film over all of the toner.

Finished board ready for etching

Etching The PCB

Now it's time to remove all of the unmasked (exposed) copper to turn your copper clad into a pcb. I use a tall plastic container (no metal) large enough to hang a panel of boards into. This style of etching will work on both sides of the board at equal rates so you won't end up over etching one side while waiting for the other to finish. By suspending the board above the bottom you can also create a stirring action with a stir plate to help agitate the solution. Periodically check on your board, it helps to flip it upside down (stirring at the bottom causes more agitation and etches faster) and otherwise move it around.

Examining a partially etched board. Note the saturated brown etchant dripping off the bottom

Ideally the entire board would finish etching at the same instant so nothing gets over etched. In reality, some sections of the board will finish first but you want to minimize the amount of time your pcb spends in the etching solution after it's finished because it will start etching under the edges of the toner. The brown liquid coming off the surface of your board is saturated with Cu(I) ions, this is the etching solution at work. Heating the solution will increase the etch rate but it's tricky to do since you're not using a metal container. Direct heating isn't a great idea because plastic doesn't transfer heat well and won't handle high heat and glassware can crack (disaster) due to thermal expansion unless it's designed for heating. If you're determined to heat the solution simply sit your etching solution container in a hot water bath. This will effectively warm the solution and prevent problems caused by excessive temperatures. I prefer to use the solution at room temperature because it's fast enough and it's easier to prevent over etching with a lower reaction rate. When finished with this (20-30 minutes) you will have a translucent pcb with copper traces hiding beneath the toner mask. Rinse the board thoroughly under running water to stop the etching process and pat dry with a paper towel.

Single board after etching - substrate material is translucent revealing copper traces on the back side

Four boards after etching. The two on the left side are the same (flipped) as are the two on the right

Remove Toner

Removing the toner and green TRF material is as simple as putting acetone on the board and wiping it off with a paper towel. However, if done incorrectly the toner will smear across the surface of the epoxy fiberglass substrate and you will have a permanent black mark on your new pcb. Although perfectly functional, it makes the board look dirty. The way to prevent toner smudges is to have the substrate material covered with acetone at all times, either by applying it liberally or by filling up a shallow metal/glass dish to soak the entire board in acetone.

Board in glass baking pan submerged in acetone. The toner is starting to dissolve

An aluminum or glass baking pan will work fine for this. I prefer the soak method because it eliminates black smudges completely while still making good use of the acetone (if you have a lot of boards to clean off). After soaking the toner for 30 seconds gently scrub the surface of the board with your paper towel while still immersed in acetone (wear gloves). Rinse the board with water and pat dry. Now you have a finished pcb with shiny copper traces and can proceed to drilling and soldering.

Board with toner/Green TRF removed to reveal shiny copper traces. Green TRF prevented pitting and acetone submersion prevented black smudges on yellow substrate

If you don't plan on building your circuit immediately (or if you want the copper to be tin plated) you should proceed to the next step.

Tin Plating, Optional

After the copper traces are exposed to the atmosphere they will start oxidizing. This isn't terribly fast, but if you sit your board around for a few weeks it will be more difficult for solder to wet the surface and make a good connection. It's possible to tin plate the board by soldering to all the exposed copper but this is only practical on very small boards. Tin plating with chemicals is incredibly easy so I always do it to my boards so I can store them and not worry about oxidation. This step is as simple as dumping some of the Liquid Tin or Tinnit material into a plastic (not metal) container and soaking the pcb for 3-5 minutes.

Board submerged in MG Chemicals Liquid Tin solution

Wear safety goggles and rubber gloves as both of these products are acidic. Liquid Tin is better because it's completely dissolved and doesn't require heating. Tinnit requires heating and never dissolves so it's more difficult to work with and get back into the bottle because it leaves undissolved material behind. In either case the copper traces will quickly change to a silvery tin color. When finished with the Liquid Tin/Tinnit just pour it back into the bottle, there are a lot more tin plating chemicals remaining in the used solution. Rinse the board and pat dry. The pcb is now shelf stable and can be stored for extended periods and soldered at your leisure.

Four etched and tinned boards - drill/solder at your convenience

Apply Silkscreen, Optional

If you want a silkscreen layer on your pcb to identify components you can do so by repeating the Toner Transfer steps above. Simply print out the silkscreen information by choosing the appropriate layers to display in Eagle. Flip the silkscreen pattern over onto your pcb and run through the laminator/clothes iron again. After cooling with water and removing the paper you will be left with a copy of the silkscreen info adhered to the pcb. The special toner transfer paper should be used for this since it doesn't leave paper fibers stuck to the silkscreen. If you hate the look of a black silkscreen and would rather have a white one, you can use a sheet of white TRF foil to cover the toner with white plastic. Applying white TRF is exactly the same as green TRF, just cover the toner, fold the film over the front of the board, and run through the laminator 3 times. You can also have a green silkscreen by using the same green TRF you used while etching. I typically don't bother with a silkscreen since I build my own circuits and can easily look at the Eagle layout to see how the components are aligned.

Drill Holes

You can drill a hole by any conventional means but a good drill setup will make this process as painless as possible. Drilling holes is generally unpleasant but using all surface mount components is impractical for a hobbyist. You can't prototype easily with them and therefore you would need to maintain a through hole and surface mount set of common components (resistors, capacitors, diodes, LED's, IC's, etc). It's easier to embrace the fact that you will most likely be drilling holes (even if they're only for mounting screws). The best method for doing this is to get a high speed Dremel tool and a set of carbide bits. High speed steel bits will work (until the epoxy fiberglass dulls them) but the holes aren't as nice. Carbide bits maintain a much sharper edge and cut clean holes without frayed bits of fiberglass sticking out. My preferred drill setup includes a variable speed Dremel tool and a Dremel drill press with a custom laser sight for positioning the hole.

Dremel drill press with #66 carbide drill bit installed. A custom laser sight provides fast and accurate positioning


Also a small light (joule thief) beneath the drill press center hole will highlight the traces in transmitted light and make drilling a lot easier.

Dremel drill press with Joule Thief light shining up from below the board. Transmitted light highlights pad locations making drilling much easier and faster


This is very simple to do and makes it possible to drill for long periods of time without brushing away the shavings. Although the drill press is low quality, it can be tightened up to remove as much slop as possible and ends up working very well for drilling pcb's. Choose a drill speed that minimizes vibrations (10-15k RPM) and an appropriate feed rate. Don't slam the bit into the board and don't go so slowly that you're manufacturing epoxy fiberglass powder, you want to see little 'noodles' of drilled out material. If you're doing this right a single carbide bit should last for 10,000 holes or more. If there is horizontal movement while your bit is in the hole you will most likely be breaking bits constantly. The hardness of carbide bits makes them extremely brittle and they will not bend like a high speed steel bit. A small but critical step is to cover the drill press handle with a piece of foam or something similar to deaden the vibrations. Before I added foam to my handle I drilled over 3000 holes in a weekend and had numbness in my fingertips (and brain, it's boring) for several days afterward.

Hold the board up to a light source to look for missed holes

Separate and Trim PCB's, Optional

Now that you're finished you may want to cut your panel of boards apart and/or trim your pcb. A band saw works best because you can make straight cuts partway into a panel and then back out.

A bandsaw cutting the first pcb from a panelized board

A hacksaw would also work but it will take a lot more effort. I used to cut boards with a heavy duty metal shears but it tends to make an ugly edge and can actually bend the board slightly. It's also incredibly difficult to squeeze the shears so only attempt if you're very determined. Scoring with a utility knife and breaking over a hard edge will work but will create ragged edges. In any case you can clean up the edge with some sandpaper to your liking. Go forth and solder your custom circuit(s) together to see if they work!

34 brand new pcb's (8 different designs) ready to do your bidding

References

  1. Build Your Own Printed Circuit Board by Al Williams. I read this after I learned everything the hard way. Goes through a design with Eagle and the toner transfer process of etching a pcb
  2. HCl/H2O2 etchant description. The source of my etching solution information
  3. Tons of info about PCB fabrication here. This page goes into different varieties of paper to use for toner transfer
  4. Hackaday has a concise description of basic toner transfer process that includes some videos
  5. This page has absolutely everything you will want to know about the HCl/H2O2 etching solution, especially the Chemistry behind the reactions. There is a nice picture of the etching solution at various stages of saturation
  6. Videos of the entire pcb fabrication procedure
  7. Pulsar Pro FX manufactures the toner transfer paper, green TRF and white TRF mentioned above
  8. Laminator information and comparison to clothes iron