How to etch printed circuit boards (PCBs) at home

June 14, 2007

I've been wanting to make my own printed circuit boards for a couple years now and anyone who's seen my spaghetti mess of soldered wires that are my usual circuit boards can understand why. My friend Jerry and I have been experimenting off and on with transferring PCB designs onto copper clad boards for a year or two. Being the frugal people we are, we tried several methods suggested on the Internet. These all consisted of using different types of paper, but the basic method is the same. You print out your PCB design (copper traces) on a laser printer. Then through heat and pressure you transfer the laser printer toner onto a copper clad board. This is generally done with an iron for most hobbyists. Our success was not the most encouraging as we often ended up with several traces missing or incomplete.

A couple months ago my friend Justin, while dwelving into electroecthing metal, asked if I wanted to split an order of Press'n'Peel PCB Blue film. This is special "film" that works just like I described above, but is specially designed for transferring PCB designs. I took him up on the offer and tried it out. It works wonderfully! At least compared to all the other papers I'd tried. So now I had a printed circuit design on some copper clad board. The next step is the actual etching, to get rid of all the unwanted copper and just leave our signal traces.

WARNING! This process involves very dangerous chemicals! All safety precautions must be taken when etching PCBs! This includes eye, hand and skin protection! Due to toxic fumes, it must be done in a very well ventilated area (ie outdoors)! All etchant solution must be disposed of properly! Do NOT pour it down the drain!

The basics of etching a PCB are very simple. You place the copper clad board with the toner resist on the traces into a solution of etchant. The etchant will dissolve the copper, except where the resist is located. Once all the extraneous copper is dissolved, remove the toner resist with some acetone and bingo, you've got a PCB. The only thing left is to drill some holes.

Step 1: Transfer your design to the copper clad boards.


When done, your boards should look similar to this. Note in the second board there is one spot (circled in green) where the toner did not transfer and there was a break in the trace. I used a Sharpie marker to bridge the gap and complete the trace. This quick fix works to correct any small errors in the toner transfer.

Step 2: Setup your etching supplies and work area


Here you can see about everything you need to etch. I'm using a small plastic container I bought from the dollar shop to do the actual etching in. The plastic "cage" you see in the left middle I made out of another $1 basket and will be used to hold the boards in the solution. On the right middle is an airation unit. This one is specifically designed for PCB etching as it has a block at the end of the hose with 5 small holes drilled in it. This block is placed at the bottom of the container to provide agitation and help speed up the etching process. On the top left are all the chemicals you need. The muriatic acid can be bought at most hardware stores. Muriatic acid is 31.45% hydrochloric acid, so be VERY careful with it. The hydrogen peroxide (3%) you can get at any supermarket or drug store. The baking soda is for neutralizing the etchant after we're done. The yogurt cup is for measuring the chemicals. The recipe we're using is 3 parts hydrogen peroxide to 1 part muriatic acid.

Step 3: Setup air pump and add hydrogen peroxide to container


Step 4: Add muriatic acid to container and put the boards in the holder


Step 5: Into the acid it goes!


Generally it takes about 5-7 minutes to etch the boards.

Step 6: Now the waiting begins.


Below is what the solution looks like after one minute. You'll note a distinct blue color, that is from the copper being dissolved. Below are a series of shots of the boards as time progresses.






Step 7: Remove the boards and neutralize the etchant


In the first picture, you can see the pH of muriatic acid using litmus paper. It's around 1-2, which is a VERY strong acid.
So lets SLOWLY add some baking soda to the etchant until it gets back to a pH level of near 7 (neutral). When you add baking soda to the solution, it will foam up quite a bit, so do it slowly. Oddly it seems the most foam and violent shortly before it's reached neutrality.


Step 8: Test the etchant


When the etchant stops reacting with the baking soda, test the pH. Keep adding baking soda until it's close to 7. You can then store the neutralized etchant for proper disposal. Contact your local hazardous waste disposal facility for information. Do NOT pour it down the drain, even though it's been neutralized. It still contains alot of dissolved copper, which is very very bad to pour down the drain.

Step 9: Success!


Here's what the boards look like after they've been etched. Note the green circle around the spot where I used the sharpie to bridge a gap in the transfer. It worked as you can see in the next picture.

Step 10: Remove the toner resist


Use some acetone to remove the toner resist. The only thing left now is to drill the holes!

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