Ecthing a DIY Circuit Board

Filled under: Electronics

Date posted: December 29, 2009

 

Overview:

When it comes to acquiring prototype circuit boards requiring SMT capabilities you can send off for them, pay a hefty price, and wait a few weeks or you can just make your own. This is a photo log of the latter.

 

The Process:

Creating your own PCBs involves quite a few steps but nothing overwhelming. Here’s a quick list of the basics.

  • Design the board’s artwork.
  • Print the design on transfer paper.
  • Cut and prepare the raw copper clad.
  • Transfer the toner from the transfer paper to the copper.
  • Remove the transfer paper.
  • Mix the etchant.
  • Etch the board.
  • Remove the toner.
  • Inspection.

Not to bad, eh?

 

The Etchant:

The etchant going to be used is cupric chloride and can be obtained by mixing the house hold chemicals of muriatic acid and hydrogen peroxide. For a full indepth writeup of the chemical process visit: http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/index.html

 

The Photos:


The first thing is to have the PCB artwork drawn up in CAD. The program I used was DipTrace as it quick to learn and easy to make custom part layouts. Ideally the schematic is first created then have the program generate the layout but in this case I jumped to making the layout manually.

When drawing up the traces make sure they are extra wide because the etchant will remove more area the toner covers.

This is a gathering of the majority of the tools and materials required. Being a preliminary assembly of items there have been a few items which found to be needed and procured during the project. Such as: paper, tape, steel wool, storage container for the etchant, paper towels, long sleeve protection wear, loupe, soldering equipment, and music.

Now that the size of the board is known the copper clad can be cut down to size. The copper clad used in this project was bought from Radio Shack and is FR4 1oz.

Scoring both sides will lessen the chance of a uneven break. Also, to snap the pieces apart place the score line at the edge of a hard stable surface and place even pressure along the piece in a single quick firm action.

The copper clad comes with a protective layer of material to help prevent oxidation of the copper. This must be removed before applying the toner. Steel wool is a great chemical free solution to remove the protective layer. The wool used was rather coarse but not so much that it removed too much copper. Let’s set this aside for a moment.

Printing the layout onto transfer paper is idea however using thin and glossy ad paper will work in a pinch. The more glossy the easier the toner will transfer to the copper and the more thinner the easier to rub off the paper in a few steps from now. The printer needs to be a laserjet because the toner is plastic which prevents the acid from eating the copper beneath hence inks will not work. A trick to prevent paper jams is to tape the ad paper to a standerd sheet of paper. Any laserjet should work fine, for the one I used is from 1993. The toner was low in this printer which made a few non solid areas in the printing which is OK because they can be fixed with a touch of solder later on.

Toner side down, lined up, and ready to go. Also, two printer paper cutouts and a power towel are present to  help spread the heat and avoid any missed pockets due to possible unevenness of the heating surface.

 

Ok, now the toner needs to heated enough to melt and stick to the copper. Using a normal household iron set on high and with enough pressure the toner will begin to melt onto the copper. After a minute or so the copper will become extremely hot to the touch. The amount of time required is not much, for this setup I only heated the transfer/clad for about two minutes on the highest heat setting.

 

The paper is no longer is required and needs to be removed. A simple bath of warm water a gentle soap will begin the removal process.

 

After a few minutes the paper is now ready to be gently rubbed off. A gentle rubbing action with the thumb is all that it takes.

 

The paper is now all gone, well, mostly gone that is. As you can see there are a few fibers left sticking to the toner. This should not be a problem.

 

This plastic coated wire handle will be used to place and remove the copper clad from the etchant.

 

This is the outside makeshift work surface mostly prepped and ready to go. For safety this step was performed outside amongst cool zephyrs (well ventilated) and for body protection wearing long sleeves, rubber gloves, eye goggles, and a face mask is advised. The solution is two parts peroxide one part muriatic acid. And remember, always pour acid into water.

 

After adding the hydrochloric acid to the peroxide visual confirmation of the chemical reaction began in just a few short seconds. Also, chlorine gas was present during the reaction which really enforces the need for good ventilation and safety equipment.

 

After about five minutes we now can see the fiberglass surface begin to show. The container began to warm due to the exothermic reaction taking place.

 

Now there are only small hints of copper left to be dissolved. The board can’t be left in there too long or the acid will continue to eat away at the traces despite the toner overlayer. Also keeping the solution agitated will quicken the etching process.

 

Gently drying the board.

 

Looking great, the copper not needed is gone! You can see the paper fibers still attached to the melted toner. Now it’s time to remove the plastic toner using Acetone.

 

Here we can see the toner all removed. This being my first DIY PCB I was not quite sure how to remove the toner with the Acetone. I used a paper towel and rubbed it off. Well, the toner removed quickly but it smeared onto the fiberglass making a bad presentation of such a great outcome. So a dabbing action seems to be the trick here.

 

This broken trace is due to a low toner bad spot during the design printing process. No worries, it’s easy to rectify.

 

Remember when I said the paper fibers on the board should not be a problem? Well it turned out that there are a few areas which did not etch fully away because those said fibers blocked the etchant from reaching the copper. This problem will be avoided next time using thinner paper and by a scrupulously examining the board for any inhibiting fiber debris before the etching process begins.

 

A quick test… it works, yay! A job well done. Time to add the other drivers and the PIC MCU.

 

A close up of a few components soldered up. This was my first go at soldering SMD. With the right tools it’s easy.

 

Disposal:

If you take the time to read the chemical write up linked above you will know two things: the solution is reusable and this is not something to pour down the drain, or even onto the ground for that matter.  So be safe, mark the contents of your storage container and keep it locked away from children and really curious people that like to taste random liquids.

 

Cost:

  • Muriatic Acid (hydrochloric), One gallon (31.45%) – $6.78
  • Hydrogen Peroxide 3, One quart (3%) – $1.99
  • Acetone, One quart – 6.49
  • Copper Clad, 4.5″ x 6.3″ – $3.99 – (Enough for three boards)
  • Funnel – $1.19
  • Paper towels – pennies
  • Steel wool – pennies
  • Etching and Storage containers – pennies
  • Misc. Equipment – on hand
  • Time

If I only did this single PCB it would cost about $24.00 or so. Now considering that the etchant is reusable, the copious amounts of chemicals in reserve, and the copper clad can be found for much cheaper, the cost per board can be as low as $1.50. One online prototyping service’s PCBs cost $2.50/sq. inch, (2″ x 4.5″ x $2.50 = $22.50 plus shipping) granted those PCBs are double sided with soldermask and silkscreen, but for a simple prototype, in this case, those extras are unnecessary. The best thing about it all is the turnaround time.  A board can be designed, etched, and soldered up to have a working prototype in just a few hours!

 

Limitations:

The most considerable limitation with etching boards in this fashion is trace width. Too narrow of a trace and it will just etch away too thick and the board will not have enough space for complex layouts.

 

Conclusion:

This was my first DIY PCB and it came out great. This new capability really opens up new doors and allows more advanced projects to be taken on. Perhaps someday I will make a CNC machine and route the boards and ditch the chemicals. hmmmmmm

 

Update:

January 2010

 


All wired up and looking good, well, ‘good’ not used as an indication of beauty. =P