Etchant

[mstechca]

I'm starting to not be impresed with my etchant.

So far, my last bit of etchant from the bottle was poured into a plastic container about 3 weeks ago. I now tried to use it for yet another circuit. Most of the copper comes off the circuit board, but the copper surrounding my design is too stubborn to come off, and I see it as copper!

So what I am trying is to add salt and sticking the container next to a boiling kettle where the steam comes out

It seems to work very slowly.

Before anyone suggests buying new etchant, I was wondering if there is a common household item I can use that works just like etchant, but faster. and if there is, what kind of store can I buy it in?
Also, I don't want the next chemical to strip the etch-resist. My etch-resist is the green stuff that is sprayed on the copper on the circuit board.

 

[JimB]

There is a chemical rection between the Ferric Chloride (I assume) and Copper.

The ferric chloride turns into copper chloride and ?? (too many years since I studied chemistry).
When the ferric chloride is gone it is gone, you need some more.

If you want a subsitute which will etch copper, you could try the battery acid from your car battery.

Disclaimer: I do not recommend this as a practical soloution and accept no responsibility for acid burns on you, your clothing or the carpet!
Also, acid used to etch copper may not work very well if you put it back in the battery! :shock:

JimB

 

[MikeHibbett]

Hi mstechca,

I used to have huge problems with etching, and actually gave up for over 10 years until I came across a method that works very well for me.

1) Before transferring the image to the copper, make damm sure that the copper has been rubbed down with wet & dry, and then cleaned with something like isopropyl alcohol to remove all residue.

2) Ferric Chloride works best at around 45 - 55 %C. What I do is place a plastic tray holding the fluid in a tub of recently boiled water.

Using those techniques I went from failing to etch simple PCBs to being able to etch complicated SMD designs using 0.8mm pitch QFP packages and 0603 parts.

I'm currently using pressnPeel for artwork transfer, but I dont think that has had any effect on the etching process. Clean bare copper and warm etchant means the process is fast enough that the etchant doesn't work it's way through (or under) the artwork. And my artworks tend to have large amounts or bare copper, so the etchant is working 'harder'.

Hope that helps,


Mike.

example here: **broken link removed**
not very complicated, but the connector is on a 0.05" pitch.

 

[hjl4]

I have to agree with you Mike,
I also leave most of the copper on the board, and remove only in between traces. I find the etchant to last 10X longer, and I also first preheat in microwave to 55Celsius and fill the sink with hot water,put bowl containing the acid in there, and voila. No magic trick here.

 

[justDIY]

I also leave most of the copper on the board, and remove only in between traces.

I'll add my agreement too

if the copper's not bothering anything, leave it masked ... the difference between having to eat away the 10-15 mills between traces (or 8 to 12 mills between pads) or having to eat away eveything except the traces really saves the etchant.

I'm not sure what cad program you're using, but in eagle, theres a good command called polygon, which can be used to fill in the 'gaps' of open space between components or traces.

I normally connect the fill to ground (seems like a good idea), but sometimes there are orphaned areas (turn orphans on) which aren't connected to anything. also turn thermals off (thermals are little fingers that reach out from the fill to connect to a pad), so the fill covers your pads (dont worry, the hole will show up when you print), it often makes them 'sturdier', so they're not as likely to be eaten away or ripped off when drilling.

also, if you panelize a PCB layout using (a graphics editor) to make several on a larger piece of PCB, make sure you use a black background, so the unused and inbetween space on your panel are left masked.

as far as heat ... my feelings are mixed on that ... I find the etchant works faster when hot, but doesn't last any longer ... the amount of FeCl3 in solution is limited, heat makes the reaction take place faster, but won't get you any more FeC3l... heat can actually ruin the etchant too, it breaks the Fe*Cl3 bond, releasing tastey chlorine gas and iron oxide percipiate. From personal experience, if you're heating your etchant, do it outdoors!!!! chlorine gas isn't something you want in the house.

I'm trying to find the links now, but a couple different sites I've read recommend ways of 'regenerating' FeCl3 (ferric chloride etchant)

 

[monkeytree]

i gave up on using an echant ages ago cos the best i could was at best amess ( a few distinguisable tracks), and i got a small mini dril/engaver for about £25 and just cut lightly along the edges of the tracks and it works a treat
1. it doesn't leave any mess on the copper
2. it can do extremley thin traces
3.quicker for small circuits
4.cheaper in the long run
5.much less equipment needed
6.can be used to cut of sections of the board
7.can be use to drill the holes

 

[Oznog]

"Battery acid" is just sulfuric acid. It won't eat copper anytime soon.
Ferric chloride and ammonium persulfate are the only practical etching solutions. There aren't any good household alternatives.

Ferric chloride not only works faster at elevated temps, it allows you to use etchant that won't work anymore at room temp. I simply mounted a 1000W halogen floodlight at the liquid in a Rubbermaid container. Heats it nicely. When it gets too hot, it will fume which is nasty. Wear old clothes and a respirator made for acid gas. The heat can also soften some resists which could make pinholes or lift a thin trace, but generally this isn't a problem with most techniques.

Ferric chloride works best if agitated. It also works really well if the container is flat and the board placed face-down but not touching the bottom. The etchant gets heavier when it eats the copper and it sinks away, ensuring only fresh parts of the solution are in contact with the board.

 

[mstechca]

Thanks.

The boards I buy are always coated with etch-resist and a white layer which I must peel off before using it. The image transfers on fine, but the problem I seem to have is etching the 1/2mm spaces in between tracks.

I bet my transparencies or glass I am using are extra dirty and I'm not noticing it.

Has anyone tried using transpariencies, and actually scratching the image on to the board before exposing it? and is that even possible?

maybe then I can get cleaner results.

 

[hjl4]

mstechca,

You've described the exact process I use. Photothensitized copper boards.
You have your circuit image on transparancies, you go in your dark room.
Put copper board down copper face up, then your circuit image, then your clear plastic or glass plate to hold the transparancies down, expose it to UV light for 3-5 min, turn light off, and then dip in developer, then rinse, then etch, and rinse again.

Your result is a perfect and clear circuit.

I have had bad ones, because I overexposed it or the plate glass was'nt sitting perfectly flat on pcboard

Have fun.

 

[justDIY]

Thanks.

The boards I buy are always coated with etch-resist and a white layer which I must peel off before using it. The image transfers on fine, but the problem I seem to have is etching the 1/2mm spaces in between tracks.

I bet my transparencies or glass I am using are extra dirty and I'm not noticing it.

Has anyone tried using transpariencies, and actually scratching the image on to the board before exposing it? and is that even possible?

maybe then I can get cleaner results.

sounds like you need to expose for longer ... the light softens the resist, and the developer eats it away

make sure you set your laser printer to print with as much toner as possible, so the transparency is good and dark (set to highest res, turn off resolution enchancement or resolution reduction and any toner savers)

use a heavy piece of glass to make sure the acetate is completely flat on the board.

use plenty of light ... the instructions recommend a single 15w desk lamp, but the more the better, just have to work out the new exposure time

make sure your developer is fresh, if its old, it looks like its working, but the board won't etch right

 

[Oznog]

sounds like you need to expose for longer ... the light softens the resist, and the developer eats it away

make sure you set your laser printer to print with as much toner as possible, so the transparency is good and dark (set to highest res, turn off resolution enchancement or resolution reduction and any toner savers)

I agree the problem is likely residue from an incorrect exposure time.
It depends on which system he's using. I use Riston film which is hardened by exposure. Unexposed resist is the stuff that washes away.

I found using 2 transparencies was FAR better. Coming off a Kinko's copier, I got like only 85% light blockage (used a photometer under nothing but UV light and slipped the transparency between them). This appeared to be better than I got off a laser printer and WAY better than inkjet. I made a fine line alignment pattern on the corners of the original work and used them to align the two transparency copies exactly. Still, with a copier pinholes or faint streaks could be a problem, so I learned to copy to transparency once, move the artwork 1/4", copy again. Then the flaws from the copier won't align on both transparencies.

Best thing is take an exposure sample. Put a black piece of construction paper over 4/5ths the board. Expose for 8 min. Turn off the UV light, slide the construction paper back 1/5th the way, expose for another 2 min, repeat. Develop and start etching. You will see the point where it got enough exposure. Be sure you use the developer at the prescribed temperature.

 

[mstechca]

expose it to UV light for 3-5 min

I have had bad ones, because I overexposed it

I expose mine for at least one hour, because 1/2 the time when I do it between 10 and 30 minutes, the etch-resist is very faint, and the chances of it disappearing after developing are higher.

I expose mine under a halogen lamp. It is brighter than an incadescent bulb.

I think someone needs to find me a better exposure time, because 5 minutes to me is way too low.

 

[Nigel Goodwin]

I expose mine under a halogen lamp. It is brighter than an incadescent bulb.

I think someone needs to find me a better exposure time, because 5 minutes to me is way too low.

You need to use an ultra-violet light, visible light doesn't contain enough UV to do the job.

 

[justDIY]

I found using 2 transparencies was FAR better.

exactly!

i've done that in the past, especially when making a board with fine (less than 16 mil) traces or tight smd patterns ... but its a real chore to line them up exactly.

i recently made some 4x6 panels; one last weekend, one last night, the first came out excellent, the second, took longer to develop and etch, it had some residue problems ... admittedly I took shortcuts, but all the pcbs in the panel came out good, the residue luckily only effected marks I use for cutting.

I attribute the residue to using developer which had been mixed on Sunday, used once, and left in a 'somewhat' sealed plastic container until last night, and used again... the developing process seemed to be normal, but inspection of the board under a bright light showed an odd residue/film on it ... it etched, but took a long time... I probably won't try stretching the developer that long again, I get the packets to mix 1l batches for something like 50 cents each, time to order more.

 

[stevez]

A friend of mine uses cupric chloride for an etchant and insists it's better. One advantage is that it can be refreshed or regenerated. I mention this just as a matter of interest.

Personally, I'd stick with ferric chloride and follow the suggestions posted here so you make the most of what the process can deliver. Ferric chloride has the advantage in that you'll have lots of 'experience' available to you from others - and the hazards are limited and fairly well understood.

 

[chemelec]

When using Ferric Chloride, I heat it in a plastic container on top of a "Coffee Warmer" that I bought at a Second Hand Store for about $2.00. Works Very Well and keeps it at a Constant Hot Temperature.

However most of the time I Reverse Electro-Plate the coppper off of the boards, than just use a little ferric chloride to finish the last little bit.
See my article here:

**broken link removed**

However you Must have a Good Resist. I'm Not sure if those Laser Printer Transfers are good enough. Never tried that resist process, nor have I used the Peel and Stick stuff.

Take care.....Gary

 

[hjl4]

1 Hour under halogen?

You're nuts.

I have 15watt fluorescent light and anything over 5 minutes, and you went too far.

Change your setup.

Also i use transparancies made for inkjet printers, and with photoblack ink, it works beautifully.

Its all in your setup I guess.

 

[zevon8]

You may have a halogen bulb that has been coated to reduce its UV output, sometimes done to help prevent fading of whatever material the lamp is shining on. Also, halogen lamps tend to output less UV over time, so the exposure time gets longer. The cheaper bulbs are the worst, they get coated on the inside of the glass envelope ( opposite of how they are supposed to function ) and this drastically reduces their UV output.

 

[Oznog]

Standard flourescent has little UV in it. Black light flourescent (not the stupid light bulb painted purple) has tons of UV in the right range.

As mentioned halogen actually puts out lots of UV, but most come in a quartz or other shield which stops UV.

Sunlight can be incredibly strong at exposing stuff, but it's hard to regulate.

There are of course any number of ways to do copper, but ferric chloride is realistically the easier, cheapest, safest thing. Having to perform chemical analysis of solutions, deal with chlorine gas or strong hydrogen peroxide is not an amateur thing. These are unlike the weak peroxide you find in stores, 50% peroxide is somewhat expensive and can set stuff on fire.
http://www.pcbfab.com/iepart5.html
http://www.thinktink.com/stack/volumes/voliii/consumbl/etchmix.htm

 

[hjl4]

No oznog.

The fluorescent bulb I use is standard 15watt bulb you can buy for fish tank or desk lamp.(standard frosted fluorescent bulb)
Try it and you'll see.
And I know the numbers don't match, but yeah it works very well.

When exposing to the light, it is about 12inches away from board.

This setup,( i wish my camera worked ), is to simple and works everytime.