Ferric Chloride

[Onoff]

I need to do some PCB type etching, well actually etch into the face of some 1mm copper sheet. I've a couple of old 2L coke bottles of ferric chloride solution I made up from dry granules/crystals a while back.

Used, I can't remember which bottle is the newest. Is there any way of testing the strength?

Similarly can it be strained, sieved, rejuvenated in some way?

Cheers

 

[Hotstuff]

Litmus paper or PH meter.

 

[Agroshield]

You can use a (Baume) hydrometer to measure the specific gravity, which correlates with strengh. If you look at suppliers of the chemical, they tell you the relationship.

 

[voipio]

The easiest way to test the strength of ferric chloride is to ensure the solution is up to a reasonable etching temperature, or at least to room temperature, make a couple of test strips of printed circuit board with the copper exposed, or some thin copper foil, and putting them into the solution, and noting how long it takes to remove the copper.

Another way to test the strength of the solution is to use an ORP meter, which measures the reduction potential of the solution, giving a readout in millivolts. It's possible to get fishtank water quality testers that can make ORP measurements. An ORP reading of 580-605mV represents the useful range for ferrich chloride.

As for regeneration, in the past, I've just added a small amount of hydrochloric acid, which speeds up the etching reaction, but also leaves a dull finish to the etched copper surface. This is by far the simplest, and least hazardous method.

This is more for academic interest, but there are several ways ferric chloride solution can be regenerated. Not all of them are really recommended for home use. Bubbling chlorine gas through the solution will do it. Appropriate safety precautions are absolutely necessary for this! Adding sodium chlorate solution (pool bleach) and hydrochloric acid, is another method. The ingredients have to be carefully added separately (with the emphasis on separately). Adding HCl to the mixture liberates chlorine, so suitable precautions will need to be taken. A by product of regeneration by this method is sodium chloride, which can form troublesome crystals.

 

[Misterg]

can it be strained, sieved, rejuvenated in some way?

You can't make it stronger, but if you let it settle, you can decant the clear (well, greenish) stuff away from the brown sludge.

 

[chunkolini]

quite simple then.
Some well informed people on here

 

[Onoff]

You can't make it stronger, but if you let it settle, you can decant the clear (well, greenish) stuff away from the brown sludge.

So the clearer liquid sat on top is the good stuff, the sludge contains copper from the etching?

 

[Kram]

Yes it can be done, you need some basic chemstry kit, involves a few steps of distilation which are not ideal to do at home - needs to be outside.

Its cheap stuff, is it worth the effort when you can buy new?

 

[Misterg]

So the clearer liquid sat on top is the good stuff, the sludge contains copper from the etching?

Yes, although the liquid gradually gets less and less effective.

 

[Ross365]

I don't think there's an easy way of measuring the effective concentration. I'd just decant the liquid off from the sludge and do a trial run. Remember that warming it will increase the rate of reaction and I usually put some in a glass container and microwave it to something like 40'C. If it's large sheet of copper maybe that too could be warmed. I just love the smell of ferric chloride - takes me back to decades ago when I was an active radio ham . Eye protection at all times of course and the tiniest splash will make a hole in most clothing!

 

[voipio]

The easiest way to test the strength of ferric chloride is to ensure the solution is up to a reasonable etching temperature, or at least to room temperature, make a couple of test strips of printed circuit board with the copper exposed, or some thin copper foil, and putting them into the solution, and noting how long it takes to remove the copper.

Another way to test the strength of the solution is to use an ORP meter, which measures the reduction potential of the solution, giving a readout in millivolts. It's possible to get fishtank water quality testers that can make ORP measurements. An ORP reading of 580-605mV represents the useful range for ferrich chloride.

As for regeneration, in the past, I've just added a small amount of hydrochloric acid, which speeds up the etching reaction, but also leaves a dull finish to the etched copper surface. This is by far the simplest, and least hazardous method.

This is more for academic interest, but there are several ways ferric chloride solution can be regenerated. Not all of them are really recommended for home use. Bubbling chlorine gas through the solution will do it. Appropriate safety precautions are absolutely necessary for this! Adding sodium chlorate solution (pool bleach) and hydrochloric acid, is another method. The ingredients have to be carefully added separately (with the emphasis on separately). Adding HCl to the mixture liberates chlorine, so suitable precautions will need to be taken. A by product of regeneration by this method is sodium chloride, which can form troublesome crystals.

Thought it better to correct my booboo. Sodium chlorate is not pool bleach, which is sodium hypochlorite. Sodium chlorate is more commonly known as a weedkiller, though it's sale for this use is now forbidden.

 

[jmp49]

15 quid for a litre on Amazon, I'm picking my battles what I dig into of late, so I'd go for that option...

https://www.amazon.co.uk/1000ml-Ferric-Chloride-Solution-Strenght/dp/B00X2W4EFK

 

[sako243]

£18 for 5 litres

5L-FERRIC, Ferric Chloride Etching Chemical for Etching in Liquid | RS

uk.rs-online.com

Just saying...

 

[Onoff]

£18 for 5 litres

5L-FERRIC, Ferric Chloride Etching Chemical for Etching in Liquid | RS

uk.rs-online.com

Just saying...

Remarkably cheap for anything "RS"!

 

[Ross365]

I think that I'd prefer to store ferric chloride as a solid rather than a solution. Think it will keep better, and presents less of a hazard.

 

[sako243]

Remarkably cheap for anything "RS"!

Like most places RS tends to offer discounts to account holders and long standing customers etc. They've quite often dropped their price on big ticket items if you phone up and speak to a rep. Farnell is the same, knocked £1000 of an oscilloscope for me based from their website price.

Best I had was when working for a previous employer we met up with the head of Xilinx UK as I was investigating a new FPGA for a number of products (as yet wasn't even in preproduction). They, straight off the bat, offered us 80% off distributor prices. Admittedly as part of the larger company we did buy a lot of high end Xilinx FPGAs.

 

[Morris]

I think that I'd prefer to store ferric chloride as a solid rather than a solution. Think it will keep better, and presents less of a hazard.

Having had a spill that went unnoticed in my workshop I would agree with that. It ate through some stainless dairy pipe and some of the floor.
I still can't find the pack of solid that I put away safe though.