Ferric Chloride

[Wendymott]

Hi Peeps..... Spent a wonderful saturday afternoon re building my PCB etching tank....obviously replacing the ferric chloride.
The question is.... how do I decide how much quantity of crystals per litre of water.
To say these crystals are old is to put it mildly... they were bought in the early 80's and have been used and stored, Im on the last pack now, Now a days Ferric is bought in liquid form, ether diluted or requiring a 30% dilution.
My tank holds just over a litre.
Any ideas please.... say Grammes per Litre...
Being in storage for so long, even in polythene bags and a plastic container, the crystals are more like lumps, so I guess there is some moisture.
There must be some sort of ideal mixture, but I have no idea what...originally we used to mix it till it seemed "right"

[Bazz4CQJ]

Hi Wendy, I use a solution of 70g of chloride in 100cm3 water, warm that up to 40-50'C, and that usually takes ~15-20 minutes with typical clad board. I cannot recall where those numbers came from and I guess other people may well be using other concentrations.

B

[Terry_VK5TM]

Depending on where you look (on the 'net), the average concentration is 40g per 100mL or 500g per litre on some other sites.

[Wendymott]

Thanks peeps .... Bit "Variable" then Terry....... at present my concentration gives me a 10 minute ech at 30 deg C so I am about right...... Obviously if its too fast you get over cut, so I think its about right.

[Terry_VK5TM]

Sounds pretty good.

I had to go looking as I changed to Ammonium Persulphate a long time ago and now don't bother at all.

[Wendymott]

Hi Terry . As I mainly do "one offs" for personal use.. I dont use PCBWAY, however if I have a double sided project then its easier to use PCBWAY.

[Terry_VK5TM]

I'm just getting lazy (plus, in the middle of summer, it's no fun making pcb's in 40C heat in a tin shed or in single digit temps in the middle of winter )

[David G4EBT]

I'm surprised that Ferric Chloride remains the 'etchant of choice' for so many home-brewers.

It's more expensive than other options such as sodium persulphate, is messy and opaque, so to see how the etching is progressing, you have to keep lifting the board out of the etchant. About the only benefit that I can see is that while the optimum temperature for fast etching with ferric chloride is 47C, a concentrated solution will still work at room temperature, whereas sodium persulphate really needs to be at 40 to 45C.

Whichever etchant is used, for the occasional one-off PCB, a small quantity of warm solution can be made then dispensed with.

In contrast to ferric chloride, sodium persulphate is white crystals rather like salt or sugar.

When first dissolved into warm water it makes a clear liquid. In use, as copper is etched away, the etchant turns light blue. (See pic below). If stored at room temperature it will keep for many months. The solution I'm still using was made in March 2018 and I guess since then that I've made 25 - 30 small PCBs. The etchant is still clear light blue with no sludge. It doesn't keep well in cold temperatures as for some odd reason, large crystals start to form, as large - if not larger - than ice cubes, but they're not ice and don't dissolve even when hot water is poured on them.

For comparison:

Ferric Chloride crystals, £13.99 for 200g post free:

https://www.ebay.co.uk/i/26285297661...26pg%3D2386202

To quote the suppliers instructions:

'For a strong etching solution, the compound is mixed in a ratio of 1 to 1 with water. Gentler applications may be etched with a solution of 1 to 4 with water. The ideal fast etching temperature is around 47 degree centigrade but the solution works very well at room temperature.'

End quote.

Sodium Persulphate crystals - 1kG for £15.99 post free (five times the quantity than ferric chloride for £2.00 more):

https://www.ebay.co.uk/itm/1kg-Sodiu...3D220721707800

To quote the supplier:

'Used for etching printed circuit boards laminated to copper. Consumes very evenly, providing sharp contours and minimizing Undercutting paths. Etching should be done at about 40 ° C. The optimal solution for etching plates are obtained by dissolving 100g in 0.25 to 0.5 litres of water'.

End quote.

Thus, 1kg will make 2.5 to 5 Litres of etchant.

The only downside to using sodium persulphate if stored for re-use is the need to heat it up to 40 - 45C. I do that with two 75W aquarium heaters with the thermostats disabled. I use a plastic cereal container for an 'etching bath' and an aquarium air stone and pump to bubble the etchant. I monitor the temperature with an infra red thermometer. I appreciate that for the occasional PCB, most homebrewers won't want to go to those lengths, any more than they'd want to gear up for the negative UV dry film process, but will seek simpler techniques such as cold or hot toner transfer methods which are very enticing and need no investment in equipment. (The search for the 'holy grail' continues!).

Hope that's of interest.

[Radio Wrangler]

There were also those NC 'engraver' type machines which would mill away copper for making PCBs. Another option for those feeling flush enough to tool-up.

They could be slow if large areas needed clearing, or else you milled the periphery and left the centre, though this could suffer from RF coupling.

They got used by the RF development community for making small prototype boards.

[Wendymott]

Hi David and David. I have a permanent tank setup.... ex Maplin.....I acquired it when I worked in the returns dept..... commercial scrap, amateur resurrection.
The ferric is the remains of production prototypes in the 80's.. and being of yorkshire extraction loathed to not use it.
My tank runs at approx 30 deg C with air injection. The solution is now ok... got half a bag of crystals left, so eventually I will buy Sodium persulphate.
Thanks both for your inputs... David.. re the miller/router..... totally out of my scope.

[Bazz4CQJ]

Originally Posted by David G4EBT

I'm surprised that Ferric Chloride remains the 'etchant of choice' for so many home-brewers.

Well, this is a Vintage Radio forum, and that distinctive smell which ferric chloride has instantly takes me back to the sixties, so it will be in use here as long as I can buy it.

The smell of Dalo pens does the same thing.

B

[Radio Wrangler]

Ah! Dalo!

David

[Bazz4CQJ]

I still have a couple of genuine Dalo pens; pretty rare now

B

[Oldcodger]

I used to use Dalo pens till I spent time in Zimbabwe, where Dalo pens were expensive, but the large permanent markers were not and more tolerant of indifferently prepared copper.
Terry- having spent some time in warmer climes ,I'd have thought that UV would suit you better, especially in the hot season. No need for UV boxes.
Only problem with FeCl is the strength and heat of the solution. It works faster and undercuts the resist when the heat/strength compromise is exceeded.

[ColinTheAmpMan1]

Originally Posted by Oldcodger

Only problem with FeCl is the strength and heat of the solution.

Oops, there is no such compound with that formula that I know of. Ferric chloride is FeCl3 (Iron(III) chloride) and ferrous chloride is FeCl2 (Iron(II) chloride).

Colin (pedant hat removed).

[David G4EBT]

Originally Posted by Wendymott

Thanks peeps .... Bit "Variable" then Terry....... at present my concentration gives me a 10 minute etch at 30 deg C so I am about right...... Obviously if its too fast you get over cut, so I think its about right.

With homebrew PCBs, especially if designed using free software provided by firms who want you to use them to produce PCBs for you by commercial techniques, many designs seem to me to use tracks which are thinner than they need to be, and pads that a smaller in diameter than they need to be. During etching, what tends to happen is that it first takes place adjacent to tracks and pads, and then continues to etch away the larger areas. Often, the areas around the tracks and pads will be fully etched several minutes before the larger areas are fully etched. But of course, all the time that those large areas are being etched away, the etchant is also etching away at the edges of the tracks and pads beneath the etch resist.

The thicker the tracks, the larger the diameter of the pads, (as far as is practicable) and the more copper that is left on the board, the quicker will be the etching time, and the risk of undercutting the etch resist will be reduced. Etching double-sided boards poses additional challenges because as often as not, one side requires a much larger area of copper to be etched away than the other side. If both sides are etched at once, the side with the most tracks and pads will be fully etched before the side with a larger area of copper, so undercutting of the tracks beneath the resist will occur until the board is fully etched.

On the few occasions when I've etched a double-sided board, I've etched one side first, with the other side covered with sticky plastic (Fablon etc). Then when the exposed side is fully etched, having removed the Fablon and drilled a few registration holes from the etched side of the board to accurately position the mask or artwork on the unetched side, I've covered the etched side of the board with Fablon and etched the second side.

It may sounds a bit of a faff, but it ensures a successful end result, especially if the PCB is quite large (say 15cms square) and the etching time is longer than a much smaller board.

To give an example of a double-sided design which - if both sides were etched together would result in undercutting - I've attached the artwork of a PCB I've picked at random from Practical Electronics (June 1980). It's 11.5cms x 12.5cms and is for a guitar tuner, but that's irrelevant. Yes, it's 39 years old, but the same principle applies to any double sided design which has many more tracks and pads on one side than the other, as is invariably the case.

Suppose both sides were simultaneously etched.

The underside (Bottom picture) has a much smaller area of copper to be etched away, so would be fully etched before the topside. By the time the underside was fully etched, the area around the tracks and pads on the topside would have etched away to an extent but there would still be a large area of 'redundant' copper to be etched on the topside. While that is happening, the etchant will be undercutting the tracks and pads on both sides of the PCB, but more so on the underside. As to the design, some (not all) of the tracks could be much thicker, and the pads larger. Unless each side was separately etched while the other side was protected as I outlined above, I think it would risk failure.

With so many pitfalls, it's easy to see why so many who have a go at homebrew PCBs throw in the towel.

[ThePillenwerfer]

When I started making PCBs I used sodium persulphate and was pleased when it ran out so I could switch to ferric chloride. I found that the former went off very quickly in storage and I usually had to make a new lot every time I needed it and it was very picky about the temperature it would work at.

I bought a litre of ferric chloride liquid for £9 and for use with copper this is diluted with 30% water so I effectively got 1.3l. I've found this suits me much better and the opacity problem is more than off-set by it's speed or action and being less fussy about temperature.

Each to their own of course.

[Oldcodger]

Originally Posted by ColinTheAmpMan1

Oops, there is no such compound with that formula that I know of. Ferric chloride is FeCl3 (Iron(III) chloride) and ferrous chloride is FeCl2 (Iron(II) chloride).

Colin (pedant hat removed).

Colin, my ancient chemistry remembrance is suitably admonished.

[Terry_VK5TM]

Originally Posted by Oldcodger

Terry- having spent some time in warmer climes ,I'd have thought that UV would suit you better, especially in the hot season. No need for UV boxes.

I did use UV, but I used to make pcb's for other people, so 40C or not, the shed it was (the gear is still in there, not used in several years now, looked the other day and the spiders are having a field day, s'pose I should clear it out).

Originally Posted by David G4EBT

With homebrew PCBs, especially if designed using free software provided by firms who want you to use them to produce PCBs for you by commercial techniques, many designs seem to me to use tracks which are thinner than they need to be, and pads that a smaller in diameter than they need to be.

When I started doing this commercially, the first software I used (which I have forgotten the name off) came on a 5 1/4" floppy and drew tracks exactly as you described, so thin, if you sneezed you could almost wipe it off the pcb.

Why they did that I'll never know ("they" will say economics or some similar lame excuse, but the amount of rework will have washed that down the drain).

I did develop a technique to fatten up the tracks with that software but then moved to other software that gave much better control over track and pad sizes.

[Wendymott]

Hi Peeps... as in all threads there are totally or nearly totally differing views, Ferric Chloride, sodium persulphate, Uv, Hot Iron, my method of UV and photo resist... the combinations are many and varied, I think its going to be a continuation of Ferric C.. and UV coated copper.... it works for me... so I will let it alone.
If as is stated sodium persulphate wears out quickly, thats not for me..until I replaced the last lot of Ferric C, it had been in the tank for ages, I only replaced it as the tank had a slight leak and wanted a repair, which involved a total dismantle and rebuild.
Another thing is that when I generate PCB artworks, I leave as much copper as I can on the board, this helps reducing contamination of the chemical with copper, it may take a little time but with my Software "Diptrace" its relatively easy.