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Old Jan 26, 2006, 01:28 PM
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Elmwood Park,NJ, United States
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PCB etching problem

I have been trying to make PCB,s for about a month now, and i have had many un-explainable results. this next one just baffles me. if you look at the picture below, you will see my newest copper board after etching. when i ironed the toner to the PCB, the toner transfered almost perfectly. there were only about 15 (almost microscopic) holes where the toner didnt stick.


i then threw the board in a container of etchant, which was then surrounded by hot water. after about 35 minutes of etching, i rinsed the board off with water. ALL of the toner was still on the board. none of it came off in the etching process. i then rubbed the toner off with acetone, and to my surprise, there were MANY holes in the board. you can see the holes in the left picture. the right picture is the back of the board. there are fewer holes on the backside. the holes on the backside are where the toner didnt stick to the board in the ironing process.

how come i have many holes on the front side, and fewer on the backside? this cant be a toner pronblem. if it was, then there would be an equal amount of holes on the front and backside. it is almost like most of the holes are only halfway deep

also, if you look close enough, my board is VERY red in some spots with alot of holes. it is almost like rust. it is harder to see in the picture.

i know the baord should still functiuon good, but i am just curious of why this happened.
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Old Jan 26, 2006, 01:46 PM
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Texas, Plano, USA
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It could be a couple of things.

1) It could be the transfer paper - the toner is only as good as the paper, make sure you are using good photo or glossy paper.

2) You are etching too long


Copper doesn't rust like iron, it can oxidize and become green.
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Old Jan 26, 2006, 01:50 PM
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i am using the Pulsar TTS paper. the image transfered fine. it was very dark, with very few holes.
when i took it out of the etchant, there were no noticable holes. all of the toner was still on the board. when i took the toner off with acetone, there were holes under the toner, but they werent noticable form the back of the board.
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Old Jan 26, 2006, 02:09 PM
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Did you touch up pcb with a sharpie before etching?

Maybe to hot an iron during transfer.

I think you are also etching to long.

Dave
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Old Jan 26, 2006, 02:45 PM
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Quote:
Originally Posted by jonathan8388

how come i have many holes on the front side, and fewer on the backside? this cant be a toner pronblem. if it was, then there would be an equal amount of holes on the front and backside. it is almost like most of the holes are only halfway deep
The only holes you will see on the rear of the PCB are those where the copper has been etched right the way through because the copper is protected by the epoxy glass at the rear. On the copper side you are just seeing pits. Before etching it is very difficult to see pinholes in the toner because they only need to be very small to cause the problem and the contrast between copper and toner is not very high.

I agree with Dave that you are etching for two long, it should only take a few minutes especially if you are heating the etchant. It is better to keep taking the board out to rinse and inspect than to leave it in for long periods.

Graham
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Old Jan 26, 2006, 04:18 PM
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Does this mean that the Etching is my problem? what i did was i filled a tupperware container with boiling water. then i took a smaller tupperware container with the etchant and PCB, and put it in the boiling hot water. after about 15 minutes, i replaced the water with fresh boiling water. then i took the PCB out after 35 minutes.

when i took the PCB out of the etchant, and rinsed it off, i inspected it CAREFULLY with a 16X magnification jewelers magnifying glass. all of the toner was still on the board. it was very dark, and i only saw a few VERY small pinholes that were caused in the ironing process. how could the etchant make many more pin holes buried under the toner?
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Old Jan 26, 2006, 05:09 PM
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You may not see the holes, but they are "large" enough to allow etchant through. I hope the tupperware you are using will not be used for food . As stated previously, the contrast between toner and copper is poor. There should be NO pinholes at all. Your iron may be set too hot, or the toner is not coming off smoothly. The pinholes may "connect" under the toner to spread the etchent. I would certainly reduce the time etching especially if it is heated.
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Old Jan 26, 2006, 05:22 PM
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The faster you etch the less pitting and undercutting you will see. Heating the etchant is not enough - you need to either move the etchant around or move the object being etched. Not sure what etchant you used but be aware that an etchant like ammonium persulfate does not work well if it becomes too hot. 40C is a good temp to aim for.

Michael
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Old Jan 26, 2006, 05:51 PM
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Epilot, i am using Ferric chloride. can we confirm that this is an etching problem, and not an ironing problem?
when ironing, i iron the board for 2 minutes with the iron at ists hottest setting. i then soak the board in water, and the toner transfer paper automatically seperates from the board within 2 minutes. after the paper seperated from the board, i noticed a few pin holes where the toner didnt stick to the copper. could the etchant have seeped through these very tiny holes, and traveled through out the board?

if this is true, would quicker etching solve the problem?

i didnt move the board much while etching. the only time it moved, is when i checked it every 7 or 8 minutes.

How long SHOULD the average etching process be?
should it be 10 minutes if the etchant is heated and agitated?
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Old Jan 26, 2006, 07:45 PM
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I finished another board. this one i ironed for 2 1/2 minutes. after i ironed, and seperated the paper, the toner had a few small holes. i touched up ALL of the holes with a black permanent sharpie. i even touched up places that didnt have holes, so i basically touched up the WHOLE board with the marker.

my only choice was to do the etchant outsied in 30 F temperatures. with the etchant surrounded by hot water, and constantly (and aggressively) agitated, i found that the MINIMUM etching time was 20 minutes. when i finished etching, i took the toner off with acetone. the board basically looked the same as my first one. it looked like swiss cheese.
as a last ditch effort, i scrubbed the board agressively with a scotchbrite pad for about 5 minutes. this lessened the appearance of the holes.
i dont want to beat a dead horse here(expression ), but why am i still getting holes in the copper? i touched up the whole baord with a sharpie, and etched for only 20 minutes.
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Old Jan 26, 2006, 09:31 PM
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Shoot and post a pic of the board with the copper cleaned up and before you iron on the mask. The pitting may be there before you iron on the mask.

You won't get perfect boards etching them at home and at some point they are "good enough for who it's for" or "close enough for government work" etc. The pits will provide a porus surface for the solder to really get a good grip

I wouldn't knock myself out striving for perfection and solder that sucka up already.
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Old Jan 27, 2006, 05:02 AM
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Tim is correct . To know if its the ironing or the etching I would do a small experiment. Get a scrap peice of copper clad and draw on it with a sharpie. Now etch that in room temp, do not use the heated water. Etch it for about 8-10 minutes, then remove the sharpie with acetone. If you have pits, its the etching. If you have no pits, its the ironing.

That last board John, looks pretty good to me (better than mine). It doesn't have to look pretty it just has have continous traces without short circuits. You can use a multimeter with a continuity tester if you have a doubt.
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Old Jan 27, 2006, 07:58 AM
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Part of it depends on the thickness of the copper. US made boards are rated in ounces, the only real way to be sure is to look at the packaging. In room temp fresh ferric chloride, with constant gentle agitation, a piece of 1/2 ounce board takes 20 minutes. One ounce board takes about 35 minutes. FWIW, I do not like heating fc, it give off nasty fumes. I know it speeds etching up, but when things go faster, they go wrong faster too. Until you get dialed in, faster etching reduces the time latitude between over and under etched, less margin for error.

Dave
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Old Jan 27, 2006, 08:49 AM
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try it cold, perhaps the heat is affecting the sharpie and toner. Fundementally acid must be getting past the mask. Bear in mind that the holes in the mask may be much smaller than the pits seen in the board because the acid will undercut the toner.

Cleaning the board well before adding the toner will help a lot with the etching time and toner adhesion and another thing to check is that you are not leaving clay from the paper between the toner on the board after ironing. I rather like Bob Baileys technique of using PTFE plumbing tape as it avoids that problem.

Graham
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Old Jan 27, 2006, 10:56 AM
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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.
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