John Wells, M5AML. QTH: Derby, IO92GW.

ETCHING PRINTED CIRCUIT BOARDS

The simple method I use to create PCBs

 

Firstly the PCB (printed circuit board) design is printed or drawn onto paper.  This paper is then taped to the copper-clad board that will be the etched PCB.  

Using a punch or nail, and a hammer mark through the paper onto the copper where each hole should be drilled.  Once this is done remove the paper template.  You should then have a copper board with marks on it.

Then take an etch-resistant pen such as an OHP pen (Stabilo etc.), a laundry marker or even a gardening tag marker (i.e. free with Spalding catalogue) and draw your tracks on the board. Make the tracks as dark and as thick as you can especially where the holes will be drilled. Try to cover most of the board with tracks so that you don't have to etch too much copper off.


Let the ink dry then inspect the design for any faults and re-ink any parts that look bare. You may find that some pens tend to drag the ink off the board so this is the best time to go over the bits that have been missed.  If you make a mistake you can scratch ink off using a sharp tool such as a nail or meter probe.  If you are making a double-sided PCB with one side as a copper ground plane then cover the ground plane side with masking tape.

Once you are happy with the board its time to prepare your etchant.

I have used Ferric Chloride but I found this to be messy especially when dribbled or spilt!
I now use Sodium Persuphate.  Like Ferric Chloride it is corrosive so take care!  I always have some kitchen roll to hand to wipe my hands and my glasses protect my eyes to some degree.  It is also wise to have some running water nearby or a tub of clean water in case you end up covered in etchant!

Sodium Persulphate can be purchased in bags to make 500ml of solution.  I use a suitably labeled and washed glass pickled onion jar to store the solution in.  Once you've finished with the solution the lid can be put on the jar and it can be re-heated next time.

To heat the solution put some warm water in an enamel coated pan on the cooker, place the jar of solution in the pan with the lid off the jar!  Turn on the gas, low, and monitor the temperature with a thermometer in the jar.  

Study the photograph on the left.

Do not heat the jar up too quickly - it will crack!!! (I have proved it)
Do not leave your Sodium Persulphate unattended!!!  

Once the solution reaches 50°C its time to etch!  But first wipe off the thermometer so that it doesn't corrode, and carry the pan with the jar and water still in it to your workbench.  Lift the jar out of the pan onto your bench. The steam coming from the pan will be hotter than you think and so will the jar!  It is best to transport your solution in this way to avoid accidents. Take care!


Now this is the fun part!  With your jar of warm solution on a comfortable, well ventilated, uncluttered bench and with some kitchen roll on stand-by it is time to watch your design materialise in front of your eyes!

Pour some of the warm solution into an old plastic margarine tub (or similar).  Place the PCB to be etched in the margarine tub. Now gently rock the margarine tub from side to side to excite the solition - this helps the etching process.  Don't worry if your board moves about in the solution.  The photo on the right shows a board that has been put into some solution in a margarine tub ready for etching.

You need to watch your board carefully as you etch because the copper can disappear very quickly.  At first nothing seems to happen except a few bubbles forming on the board but suddenly the un-inked parts of the board begin to disappear, rapidly!  I find it best to rest the tub lid on top of the tub to help keep some of the heat in but visually check the PCB every 30 seconds or so.    If the etching PCB is left unattended too much copper can be etched off and your board will be ruined! 

As soon as the tracks have been formed pour the solution back into the jar (put the lid on!) and take the PCB out of the margarine tub.  Rinse it off, sand it down and buff it up to remove ink.
Now using the punched marks you can drill the holes for your component legs to go through.  A 1mm drill will do but 0.75mm holes work better for the majority of components.  I use a small variable-speed Como motorised drill.

I find it is a good idea to go around the tracks with an ohmmeter to make sure there aren't any minute breaks or shorts.  Any shorts can be removed with a knife, meter probe or pin.  Any small gaps can be wired across,


The sodium persulphate solution can be used many times but will take on a blueish tinge with use.
 

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