Introduction: Etching PCBs With Pickle Juice
When I am asked a question about science, I advise people to do the experiments or to build the device and play it safe. It’s not important if your device works or not, it is what you learn from your effort.
“I have not failed. I've just found 10,000 ways that won't work.” Thomas A. Edison
Earlier this month a young inventor lost his life during one of his experiments, he made a rocket powered skateboard.
The tragic events of that day have inspired me to add a new line to the advice I usually give.
Before you start an experiment stand back and look at what you are about to do. If it looks like anything Wile E. Coyote might do in a Road Runner Cartoon.
I look for different ways to salvage gold and other precious metals from electronics using etchants and other techniques. I came up with the idea for making etchant from pickle juice from an Instructable on etchants made from Vinegar, Salt and Hydrogen Peroxide. Two of the three main ingredients in pickling brine are vinegar and salt, the third ingredient is water.
Since etching PCBs, (Printed Circuit Board) with pickle juice tickled my repurpose bone, I decided to do the experiments, and remember my own advice.
Play it safe, do not take risks and follow safety procedures. Don’t be Wile E. Coyote or do what he might do in a Road Runner Cartoon.
I will also not be using scientific terms like thermal reactive or taction contact detonation, the big words are not as important as knowing if it gets hot it goes boom.
Step 1: Selecting a Pickle
This part can be tasty, eat the pickles and save the juice. For my experiment I chose baby dill pickles.
Saving the juice is not as easy as you might think; people do three things with pickle juice. Pour the juice down the drain, use the juice to make more pickles, and they drink it. Yes people drink pickle juice, it is reputed to cure a hangover, aid in the recovery from physical exertions, and it is loaded with electrolytes. Pickle juice is sold as an energy drink, so guard your juice.
Since I wanted to avoid unwanted chemical reactions, I chose a pickle with a minimum of additives as seen on the ingredients label. Sweet pickles can contain sugar or glucose and they have the potential to turn your mix into a smoke or stink bomb. Hot pickled peppers contain capsicum and capsicum can leach into the brine from the hot peppers. Capsicum can be vaporized into the air when heated or during chemical reactions. Unless the pickles have added capsicum, capsicum from hot peppers may not be on the label, so if you are not immune to capsicum, avoid hot peppers for this experiment, you do not want to breathe in the noxious vapors from this experiment in any case.
Step 2: Reducing the Brine
Materials and tools.
2 Bottles or containers the same size.
Portable Heat Source or Stove
Now the range hood above your stove is not a proper fume hood; some do not vent outside and most don’t capture all the fumes off your stove, so use a proper fume hood or do this outside in the fresh air.
There is not much risk in heating pickling brine, I have heated pickling brine a number of times, I do not mind the smell of vinegar or dill. However my wife makes me prepare my hot pickled peppers and my hot sauce outside. To her the hot peppers make the air unbreathable. If any of these smells bother anyone in your home do this outside or under a fume hood.
Using the coffee filter, filter out any solids in the pickle juice as you transfer the juice from one container to the other.
Put the pickle juice in a pot on the heat source and simmer until at least half or more of the water has evaporated. Since most pickling brines are one part vinegar and one part water this should get you the same vinegar percentage as white vinegar.
Let the pickle juice stand until cool, once the juice is cool pass it through a coffee filter as you transfer it to a clean container. This should capture any semisolids created by the evaporating process.
At this time you may notice your pickle juice has a color to it, in my case green. This is an indication there are other chemicals in the juice other than vinegar and salt. Green probably indicates chlorophyll from the pickles. The point to this is the mix has mystery chemicals in it.
Step 3: Something to Etch
Tools and Supplies
Blank PCB board
Schematic of a circuit
I decided not to waist a good blank PCB so I picked an LM317 adjustable power supply circuit and traced the circuit out on the blank board with a black Sharpie pen. Sharpie pens are commonly used to make custom circuit boards. You could say I am doing two experiments in one, testing the etchant and testing the Sharpie ink with the etchant.
Sorry about my poor drawing on the blank PCB, it can’t be helped.
Step 4: Supplies for Testing the Etchant
Splash guard; for this I repurposed a disposable cake cover.
Mixing container; for this I repurposed a jar.
2 measuring containers; for this I used two shot glasses.
A bowl to do the etching in; for this I used another disposable container.
Pickle juice prepared earlier.
Blank board prepared earlier.
Hydrogen Peroxide 3%.
One of the advantages of using repurposed materials is the cost should you only use them once.
Step 5: The First Step in Testing the Etchant
Setup your experiment clear of anything that might be damaged by a chemical reaction.
Prepare equal amounts of the pickle juice and Hydrogen Peroxide for mixing.
Remove all leftover materials from test area.
Done all the safety gear.
Mix the pickle juice and Hydrogen Peroxide and get clear of test area.
Ideally you should use a robot to mix the pickle juice and Hydrogen Peroxide since chemical reactions can happen quite quickly and you do not want to be near the mix if it does something unexpected. This is quite possible since the pickle juice is tainted with unknown chemicals.
I had a video camera running when I did this part, just in case something interesting happened when I mixed the pickle juice and Hydrogen Peroxide. To my disappointment and joy nothing interesting happened.
Now you wait, just as chemical reactions can happen quickly they can take their time also, so wait and see if a reaction starts. Check for heating up of the container, visible fumes, and bubbling. This delayed reaction has been the cause of many accidents, not just in the lab but in the real world also.
I was target shooting a British 303 Enfield rifle a number of years ago with a friend of mine. The ammunition I was using was old, I loaded my rifle, and aimed at the target. I chambered a round, cocked my gun, and pulled the trigger. I heard the firing pin go click and nothing else happened. My buddy looked at me and said, “I heard that.”
Keeping my rifle pointed down range, I looked at him and said, “Oh cra.” And my gun went bang before I could say anything else.
Delayed detonation happens with propellants and explosives; they do this all the time so wait until you are sure it is safe before approaching them.
Step 6: Etching
When I was sure nothing was going to happen I poured the etchant into the disposable bowl and placed the blank PCB board in the etchant. At first nothing happened and after waiting a while I added a little salt. Almost immediately the PCB board started to bubble, I added some more salt and you could really see the etchant start to work on the PCB board.
Step 7: The Finished PCB
When I started this experiment I was prepared for the results to be a royal flop. I expected elements from the pickles and spices that leached into the brine as well as the calcium chloride and polysorbate to interfere with the desired chemical reactions. To my surprise the etchant worked well.
The etchant did make its way through the Sharpie ink but I think most of that was more due to my poor application than the ink.
Next I am going to try this etchant on circuit boards to salvage the gold.