Semi-OT: Etching quetion...

[freebird1127]

Hey all,

I'm creating a 400W poweramp board out of a 6"x9" 2oz. (for extra current handling capability) copper clad single sided board... design is done and I'm ready to make the board.  Because I'm using 2oz. copper, I'm a little concerned that using ferric chloride in a container at home will not produce as good results as it will those times i've made boards with 1oz copper... what do you think?  Is this okay?  Any suggestions?

Also I was wondering, is using a glass tub for etching okay with ferric chloride?

Thanks all,
Evan

[Brian Marshall]

Glass should be fine, but i wouldnt use it if you ever want to serve food in it or something.

I'm not sure about the board its self.  I have never built anything where i had to worry about the thickness of my copper traces or anything like that.

you probably want to be very sure you that whatever you use as a resist works really good, because my guess is you'll probably have to leave it in there for an hour or so.

Brian

[freebird1127]

I plan on using PnP Blue, can't think of anything better really.  I may have to find a benchtop etcher with ammonium persulphate to use.... ugh....

[Nasse]

Maybe heating ferric chloride enough helps speeding the process, if you are worried about that

[freebird1127]

What i'm really worried about is that by the time the middle of the board is starting to etch, the ouside traces will be overeaten and pitted and scored all to hell...

[Paul Perry (Frostwave)]

What i'm really worried about is that by the time the middle of the board is starting to etch, the ouside traces will be overeaten and pitted and scored all to hell...

Not if you keep agitating it, or stirring it with a brush (no metal parts on the brush, of course!).

[David]

Evan:

Would you consider sharing that schematic?

Please?

[Mark Hammer]

If I need to speed up etching, here's what I do:

1) drill small holes in the corners of the board

2) poke toothpicks through the holes to provide "legs" to keep it suspended near the surface of the etchant (copper side down)

3) warm up the back/component-side of the board with a desk lamp, a hair dryer, or these days, the low setting on my heat gun

You don't want the etchant to boil.  rather you want whatever etchant is in direct contact with the board to be maximally efficient and then fall away once it has done its ion-exchange business.

The fact that you are using a glass dish is helpful.  I use a plastic sandwich container from the dollar store for etching, and you can imagine that poking a heat gun up close means I have to be on my toes and avoid melting.

I cannot emphasize enough how spotlessly clean the bare copper needs to be to help this along.  If there is ANY finger juice on the board, with copper this thick it will become problematic if some parts slow down with respect to copper removal.

Just out of curiosity, and as a general question to people "out there", is there any product one could spray on a board AFTER having ironed on a PnP pattern that could clean the exposed copper or at least let one gently towel off the finger juice?

[Paul Perry (Frostwave)]

is there any product one could spray on a board AFTER having ironed on a PnP pattern that could clean the exposed copper or at least let one gently towel off the finger juice?

I doubt it, because anything that dissolves the oil left by your fingers, would likely dissolve the PnP blue, or toner for that matter. Maybe try alcohol, but I'm not optimistic.
Here's an idea, though.. if you put your PCB straight into a container full of water, it will stop you "accidentally" touching it before you are ready to use it. Kind of like those "anti influenza" masks don't work by stopping droplets, but by preventing you unconsciouly transferrign germs on your hands to your mouth (in my opinion).

[Nasse]

:? Sorry to stir this topic little off original topic/question but after having some similar problems but one thing come in my mind reading this thread...

The chemical "quality" of water is variable depending what you use or where you live, sometimes it contains minerals like carbonates and is "hard" or "soft" etc. Somebody (Mark Hammer?) reported PNP irregular success some time ago, and conclusion was that sometimes local water has some properties that can produce invisible oxidation or mineral layer that is troublesome with pnp. Quess it can affect toner transfer adhesion too, and maybe somehow such oxidation can resist etchant (but not very much and not for long time)

So storing etched pcb under water is good tip

Maybe some mixture of lemon juice and salt and water could be used, I have polished copper coins and some household things made of copper with such ingredients...

[Adam Shame]

Couldn't you use those plastic (not latex) food-service gloves for handling pre-etched PCBs?  Or maybe even some rubber gloves you use for washing dishes?

[Mark Hammer]

If you want to keep them away from climatic conditions, a simple way is a regular paper envelope.  You can also use plastic food wrap, although you want the drier type...if you have a choice.

When handling the un-etched board, especially if retouching with a pen, or hand-drawing, I like to use the onion-skin paper that comes on the backing of rub-on letter sheets.   That stuff is extremely non-porous.

[freebird1127]

Good Idea Mark.  Esp/w the etching method, very clever ;-)

I'll share the schematic as soon as it's hosted on a site.  Any takers?

[RedHouse]

You should be fine if you heat the ferric cloride.

To use heated ferric cloride do the following:

-pre-heat the solution in the Microwave (in container w/lid)
-place container it in a hot water bath during etching

1.) I fill my utility sink about 1/2 way up with the hotest water my pipes dispense
2.) I put the etchant into a old tupperware lidded enclosure and heat it in the microwave for like 30 seconds or so (you will see it steam when it's hot) and it wont hurt the microwave as long as it's in the lidded container.
(this procedure hasd the approval of my wife!)
3.) Place the PCB traces-up in the clear plastic container, pour the heated etchant in and put the lid on.
4.) Place the container in the utility sink which is full of the hot water, this water will keep the tempature up in the continer through out the etching process.  

You will notice a VAST improvement in etching time, a simple 3"x5" PCB will etch in a bit over 5 minutes compared to 25-35 minutes when the etchant is at room temp.

I don't need to elevate the PCB in the etchant, for me, the way to make sure to get evenly etched traces is to rock the container while its in the hot water bath, the rocking will wash the copper away so new etchant gets at the traces, and they won'y etch undercut when you etch in hot etchant.

Just be sure to watch the board and pull it when you can se there is no more work to be done on the trace side.

This method has worked well for me for years doing small runs of PCB prototyping over the years.

[RedHouse]

(gee, I guess I need to learn how to click "Preview" instead of "Post")...

Anyway, one more thing, Ferric Chloride is a "base" chemical, when you are done etching rinse the board thoroughly in cold water, then use a acid wash to stop the chemical reaction. Ordinarily one would use a tincture of hydrocloric acid (7% HCL in water) but at home one can get very good results with white wine vinegar from the grocery store, it is acidic enough to neutralize the base.

Just pour some into a container, place the board in it and wash the board when you are done etching (I use a old toothbrush) then re-wash it in cold water after the vinegar bath. It will stop the ferric cloride reaction and make the board ready for tinning/soldering.

[PeopleHateMe7666]

ill post it on geocities... ha... lol but i want that schem too,,,