PCB etching problem - Page 2 - RC Groups
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Jan 27, 2006, 11:59 AM
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Jan 27, 2006, 12:21 PM
osmium_192's Avatar
Hi all

Ive actually done a few etched boards, and i am always watching it. I move it around sand take it out every few seconds so i can remove the board at the last few seconds just when the last bit of unwanted copper is removed. BUT I still get pits in my copper.

The way i do my boards is pretty tedious. (I use Ferric cholride).

Firstly i design my board on computer. Once im happy i print one out and i use it as a drilling template. I drill my holes first, and then i draw the tracks with permaneant marker, making sure the ink is thick. This bit needs just patience since im drawing the design by just estimation to join the holes. Once done i put the board into the etchant and wait with it. At 15 deg(C) i normally just stand around watching it for about 45 mins. Usually this results in a pretty neat etching, but the ink still gets slowly dissolved by the etchant and where the ink is thin the ink is dissolved quiclky and that part gets etched.

Large pits show through, while shallow ones are pinkish in colour. That pink colour is just the colour of copper when it has a matte finish. It seems to stay pink simply because you cant sand it smooth.

Atached is a pic of the computer schematic of my small 12V amplifier at about 4 times larger. Ill add a pic of the underside tommorow.

Jan 27, 2006, 01:04 PM
Registered User
Guys, here is my experiment. this image was made just with an ink marker. you can still see a few traces. these traces wew because some ink seperated from the board during the etching process. other than this, there are no pit holes that formed under the marker. this means that the ironing, or the printing is my problem . is my problem more likely to be the printing , or the ironing?

right now, i am printing on high quality TTS paper on a 1200X1200 DPI setting. then i iron the paper onto the board with the iron on the HOTTEST setting. (on my iron, the hottest setting is linen) then i iron the paper to the baord with medium pressure for 2 1/2 minues. right after this, i submerge the board in hot water, and the TTS paper automatically seperated by itself.

the file on the right is the board printed on regular paper on the 1200 X 1200 DPI setting. it looks a little crude, but does it look dark enough?

Owen, your board looks pretty cool!
Last edited by jonathan8388; Jan 27, 2006 at 01:16 PM.
Jan 27, 2006, 01:23 PM
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bmutlugil's Avatar
Hi jonathan,

I can't suggest anything on the toner transfer method, never having tried that, but can suggest an alternative etching solution that works at room temperature and is very clean. The solution can be used many times, by replenishing its hydrogen peroxide, until it gets saturated with copper. I keep the same solution until too much hydrogen peroxide or acid is neded to keep it etching - this is a sign of copper saturation.

This is the etching formula suggested by Contact Chemie, that used to produce the Positiv20 brand of spray photoresist. It should not attack permanent ink like that from Sharpies. I used to make corrections using permanent markers.

The formula goes as:

330 ml. (cc) concentrated hydrochloric acid (%36 I guess - not sure)
70 ml. hydrogen peroxide (%35)
the rest water to make 1 liter (1000ml. or cc).

I don't know the formula in fluid ounces, etc.. I don't know if you are accustomed to the metric units ml. or cc..

If you use more acid and peroxide, the etching time gets shorter but the solution becomes somewhat unstable - the first one I made had around 250 cc. hydrogen peroxide, it kept blowing the cap off of the bottle The etching time should be less than 20 minutes with the standard solution, probably less than 10 minutes as well, but I am not sure. I have not used this since many years, nowadays we use a professional system at work - produced by Think&Tinker USA. This setup works using a sulphuric acid plus peroxide etchant.

When the used solution starts getting dark during etching, a little hydrogen peroxide is added and the process continues.


Jan 27, 2006, 03:13 PM
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caseyjholmes's Avatar
even with the toner process and sharpie markers..
I get a pitted PCB or two once in a while. This was attributed to over-etching for me, and I'm positive on this, as under etching did not yield the same results, or anything close. I use heated etchant, in a MG chemicals etching/agitiation tank (the big one)
While making the first set of Koichi transmitters, I had a board or two that were pitted, even using the photo exposure process and not the toner transfer process. I'm almost positive now, that this is an over etching problem in one way or another. It can also relate to the style of toner. Toner is porous by nature (as the TTS paper directions describe) and require a sealing layer of GREEN TRF... also sold by pulsar with their TTS paper. This should ifx the problem, and I Regret not sending some along with the TTS paper.
See if the green TRF will help you, it is made for sealing pitts in toner to prevent your problem you are having As you can see, My Koichi TX boards, although done by photo exposure, stil have a layer of green coating over the copper.
Jan 27, 2006, 03:18 PM
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Dave Wulff's Avatar
Originally Posted by jonathan8388
Guys, here is a piece of clean copper before ironing.
Dave, i am not sure how much my board weighs. all i know is that its thickness is 0.0064". i etched it outside in 35 F temperatures. it was submerged in boiling water, and constantly and aggresively agitated. it took a minimum of 20 minutes to etch. then again, i didnt put JUST the board in the etchant. i left about 1/2 an inch of copper around the board and etched.
I don't think you understood my post. It is not how thick the board is or how much it weighs, but how thick the copper coating is. The thicker the coating the more etching time. Re-read my post. Most small boards are coated with either 1/2 ounce or 1 ounce copper material, one being twice as thick as the other and requiring almost twice the etching time.
Jan 27, 2006, 03:18 PM
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caseyjholmes's Avatar
Also jon,
Be sure you print your images in black. A laser printer prints any images done in other colors as dotted lines, and not complete filled lines. This may mean changing the view of your pcb cad editior to view everything you drew as black.

Jan 27, 2006, 03:27 PM
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caseyjholmes's Avatar
I beleive the board I sent jon was 1/2oz copper
Jan 27, 2006, 05:04 PM
Registered User
so basically, i am leaving the board in the etchant too long, right? the minimum time that i could etch the board was 20 minutes, and that still meant pitted holes in the board. what do you recommend that i should do?

the toner MUST be the problem, becuase i got better results when using an ink marker. this means that the etching shouldnt be the problem.

how would i use the GREEN TRF? do i spray it on the image after printing? or do i spray it on the image afer ironing?
Last edited by jonathan8388; Jan 27, 2006 at 05:14 PM.
Jan 27, 2006, 07:25 PM
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caseyjholmes's Avatar
you iron it onto the toner image you applied to the pcb. =)
as if you were ironing on another toner image of the last one. But this time, it requires no printing of toner on the TRF. Just heat up the TRF with the iron on top of the pcb, peel it back, and viola! the TRF stuck to the toner applied to the pcb, just as you stuck the toner on to the pcb. It comes in a large folded sheet. you can cut a sheet the size of your pcb so you don't waste any TRF. The good new is the stuff is only $7
try circuitspecialists.com ... or search for circuit specialists website. They have excellent on time service, every time, no order problems or delays.
Jan 27, 2006, 09:06 PM
osmium_192's Avatar
Ive used toner before, and i find that thats always given me problems. Toner ALWAYS gave me pits, even with PCB extraction from the etchant just seconds after completion of the board. I think its a matter of how toner is just made of dust particles that are melted onto paper, So when you heat it up with an iron to transfer the toner becomes a sticky compound again, but when you pull off the paper the toner forms peaks and troughs, like what happens if you have grease between two surfaces and you pull them apart.

I find that pens give me better results, BUT you will need to draw the line and then "dot" the line over again to make the ink really thick. Its really tedious but most of the time is pretty good.

My amplifier board has alot of pits in the tracks, which is really annoying, and is a result of the thinning ink allowing etchant to come into contact with the copper.

Jan 27, 2006, 11:07 PM
Registered User
Originally Posted by caseyjholmes

digikey sells this stuff also. if it is the same, i might as well order it from them to save on the shipping cost. the part # is 182-1021-ND

can you safely say that it will get rid of most of the pits?
Jan 28, 2006, 12:56 AM
ClearView Rocks!
Quacker's Avatar
Here is a trick that I have never heard of, but discovered one day, that may help. No matter what process you use, a clean-very clean board is best for toner or resist or marking pen. Clean the board with Comet or similar abrasive cleaner. Never touch the surface after using the Comet. Rinse well. Then drop the bare board into your etchant for 10-20 seconds. Pull it out an immediatly rinse very well and dry. The pre-etched board will be cleaned right down to the atoms and have a smooth, dull surface that most things will adhere to extremely well. You can also get a hot electroless tin plating to finish the board and enhance soldering/prevent oxidation from: http://www.philmore-datak.com/DATAK.htm (bottom)

Good luck!
Jan 28, 2006, 11:56 AM
osmium_192's Avatar
NOW THATS AN IDEA.... the rough surface should take up pen and toner more readily, with more surface area and "micro pits" to help grip onto the ink.

Will try that for my next project.



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