Great Post!
Really looking foward to see your spray etcher design.
--- In Homebrew_PCBs@yahoogroups.com, <benscale160@...> wrote:
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> You may want to purchase some Copper oxide and add that to your mix. There are several sources on ebay that sell anywhere from 1/2 lbs to 20 lbs bags. Copper oxide reacts directy with HCl to produce CuCl. The more you add the higher the specific gravity goes. If you overshoot, add some water.
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> For solution maintenance, adjust your acid molarity first, then your ORP (solution color), then the specific gravity. If the SG is a little to low, dont worry, it will raise as you etch.
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> I bought a 10 lbs bag and made all the etchant I will ever need in about 4 hours.
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> For my aplication, I wanted the capabilty to etch brass and phosphor bronze plates .010 thick to make detail parts for Model Railroading as well as PCBs.
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> From the figures from the Seychell document, I calculated that I needed about four gallons of fresh etchant per cycle to do the job to etch a 6"x6" piece of brass or bronze by 50%.
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> I ended up building an etching spray tank. I will go into detail about this unit in a later post. It cooks a 6x9 PCB in about 2 minutes. It cooks the 6x6 brass or bronze in about 6 minutes. I just keep the acid, and orp in the specifed tolorances and it cuts very good each time.
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> You may be able to adopt the below procedure to streghthen your solution.
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> I must caution you that the reaction from the below procedure generates lots of heat and HCL fumes. Use a suitable container incase of a boil over. I only make 1 liter batches at a time. Wear appropriate PPE (personal protective equipment, gloves, glasses, long sleevs, face shield, resperatior, etc). Have a nuetralizer availble (ie. sodium hydroxide) incase of a spill. Have a source of running water for rinsing. Do this out doors and not on concreate (the wrath of the wife is not an option). HCL etches concreate.
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> Materials:
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> two medium sized polypropylene cereal containers (walmart)
> one large sized polyproylene cereal container (walmart
> 37% Hcl (pool supplier, home depot, etc)
> 35% H2O2 food grade (natural medicine websites, google search)
> Copper oxide (ebay)
> measuring cup
> Battery hydrometer, glass (auto parts store)
> sturring stick (I used an aycrlic rod)
> deposible plastic spoon.
> 1 gal pvc containers (us plastics)
> Plastic funnel
> fiberglass window screen
> thin paper towels/filter paper
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> Procedure:
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> Start by measuring out 500 to 750 mL of HCL and pour it carefuly into one of the medium sized containers. Put a couple of spoon fulls of the copper oxide into the solution. Careful of splashes. Use care not to get any on your hand. I have found that copper oxide will not desolve in water. Keep your spoon dry.
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> The solution will start to bubble and generate heat. Use the stiring stick to aid in desolveing the copper oxide. In additon, the second medium cereal container can be used transfer the solution back and forth as another means of desolving. The transfer method will also help get all the copper oxide that stuck to the side of the containers as well. Allow the solution to cool a bit before adding more copper oxide.
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> Repeat the above prodecure until the specific gravity is at your desired level. If you overshoot, not a big deal, simply add water.
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> Use caution with respect to the temperature of the solution when taking specific gravity readings with the hydrometer. A hot solution may subject the glass instrument to thrmal shock and shatter it.
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> Once you get to your desired specific gravity, the solution still may not look right. It will look like a muddy olive color, no problem, it is just CuCl 1. Add some 35% H2O2 and the emrald green color we are looking for will emerge. Again, use caution with this step as you are pouring into an acidic solution. Another caution here is more heat will be generated as the H2O2 reacts.
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> Pour the finished soluton into the large cereal container for cooling. Once the large cereal container is full and cool take your specific gravity readings, check your acid levels and solutoin color. Make adjustments as needed. Pour into pvc storage or equivilant bottle.
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> I also found that there was some sort of white buildup at the bottom of the containers. This may be some impurites that were in the copper oxide powder. I first used a piece of fiberglass screen material in the funnel to filter out any large impurities. I then ran the solution through a thin paper towel in the funnel for a second level of filtration. When all was said and done, there was a layer of sludge left on the paper filter.
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> Hope this helps, Please, please, please be very careful. And have fun.
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> Ben
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