Etching copper: some questions

[pkelecy]

I am developing an electrical device which uses a machined piece of copper for an electrical conductor. This is done for packaging efficiency. Because the machining process leaves some sharp edges and burrs, I thought I would soak it in Ferric Chloride to remove these prior to insulating. I've performed a few soaking tests on some sample strips of copper and am a little puzzled by the results. Although the Ferric Chloride is removing the burrs and sharp endges, it is also leaving a dark, grayish film on the copper. I was expecting to see a nice shiny piece copper come out of the etchant, once washed off. But that isn't the case as all. If I look at the surface under magnification, it looks very rough. This leads to my questions.

1. What is this film? Some by product of the etching reaction?

2. Is there a better etchant to use for what I'm try to accomplish? I was hoping to remove burrs and round edges, as well as clean the copper surface with this soaking process. That way the part would be ready for insulating without needing any further treatment. But at this point it's not looking too promising.

Thanks for any help with this. I appreciate it.

Pat

 

[svtiss]

Try this
**broken link removed**,

it leaves cooper shiny ,

 

[3v0]

The OP did not tell us where he was from. The good news is that this is a MG Chemical product which is widely distributed.

 

[Aiden1015]

I may be mistakened but I've made a few circuit boards using ferric chloride and the darker color is from the solution starting to eat away the copper in parts you may not want.what you could do is coat the perimitter you want to keep with a sharpie or nail polish. afterwards you can use a solvant to remove the resist.

but why don't you just sand the burrs off by hand?

 

[jpanhalt]

I would consider electropolishing or tumbling to get rid of the burrs. Tumbling is a very common method and is self explanatory. The object can be actually tumbled with the abrasive or in a vibrating vessel.

For electropolishing (reverse plating), the metal object to be polished is the anode. The sharp corners are "plated off" first. Bath chemistries get complicated and many are proprietary for fine polishing, but if all you want to do is remove sharp corners, I would just use an acid bath. Google will have lots of methods on electropolishing.

John

 

[pkelecy]

Thanks for all the replies.

Coincidentally, I had purchased some Ammonium Persulfate when I purchased the Ferric Chloride (both from MG Chemicals). I thought it might be a cleaner alternative. But I decided to start with the Ferric Chloride, since it was already premixed. The Ammonium Persulfate comes as a crystal powder which has to be mixed. I'll try it next and see how it does. Does anyone know the proportions of powder to water (by volume) with this?

I tried electropolishing, as someone suggested. I sent a part out to ExtrudeHone to test in their "CoolPulse" system. The results didn't look any better. The ExtrudeHone rep said that to get the best results with electropolishing an "image plate" is needed - a plate that closely follows the contour of the part you're electropolishing. That makes sense, but wasn't practical in this case, which is probably why the results didn't look any better than acid soaking.

Someone suggested tumbling, which is an interesting idea. I'm not sure if that would work in this case, as the part is rather delicate. I probably gave the impression that it is some solid block of metal. It's not. It's actually a long thin ribbon (~0.030" thick and 0.5" wide) wound in a certain shape. Still, I'll probably look into than if I can't get any better results with the ammonium persulfate (or some other).

Thanks again for the suggestions. Any others are welcomed and appreciated.

Pat

 

[svtiss]

1kg to 4 liters water or less and warming the solution will boost the etching
if you want it fast , it should be around 80 or degrees or 176f

 

[Vivian Soh]

I am new in this PCB etching process. I am trying out few methods but I still prefer using environmentally free method. Does anyone can advise me the best environmental friendly method for PCB etching?
1) Chemical etc
An environment friendly etchant.

o Possible substitute is 1 : 2 solution of Hydrochloric Acid(38%) : Hydrogen Peroxide

o Advantage is material can be easily purchased and can be INFINITELY stored and reused.

o However, no evaluation carried out yet as currently still using Ferric Chloride to cater to immediate need.

 

[jpanhalt]

Look up cupric chloride etch. It is supposed to be like yeast starter and can be regenerated continuously. It keeps growing in volume, but doesn't wear out. The copper that is etched from the PCB simply adds to the etchant.

There are various ways to make the initial etchant. Copper(II) oxide dissolved in HCl is one way. To replenish, you can just use plain air or hydrogen peroxide to reoxidize the copper(I) that is formed or use chlorine gas (which is easily made at home or available commercially). If you use air or peroxide, you need to periodically adjust the "free" acid concentration with additional HCl. Free acid should be around 1 to 2 moles per liter of etchant. The copper content is about 2.5 moles per liter.

See: Chemcut Corporation, which has a nice description of various methods for etching, including copper(II) chloride, on its site. You can also find DIY directions at: **broken link removed**

John

 

[Vivian Soh]

Hi John, thanks a lot for your helpful information. I have another question. I would like to try other chemical etching. Like Sodium Persulphate etching and Ammonium Persulphate etching. Can you draft me the procedure of the process? Please advise me the actual volume needed. Thanks a lot.