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Printed Circuit Board fabrication via Resist / Etch


It is possible to make good quality circuit boards using some form of echant resist on copper board (iron, then wetting the laser print and loosening the toner) then etching with Ferric Chloride, Cupric Chloride, or some other echant. If one sticks to 0.030" PCBs then they can be cut using regular scissors. For double sided boards / or single sided with through hole parts, center punch then drill with a dremel on a drill stand or stick to SMT / single sided and solder on wire-wrap wire for bridges.

Be aware that there are some problems with this method, chiefly due to incomplete or light traces. You'll need to check the board carefully after you make it.

For very thin copper (1/2 oz) scrubbing the copper with a sponge as it etches can make a significant difference in the etching speed. Etching times as little as one minute have been achieved. 1 The effect is much less pronounced with thicker copper or when using persulfate etchant. Spraying or otherwise moving the etchant over the board surface provides the same benefit, but the sponge allows one to etch without a tank.

PCB's can also be made on non-traditional stock such as thermal tape (see: video material) which is then mounted to stock or directly to a heatsink for excellent thermal dissipation.

Also see echant resist methods:

Etchants

Ferric Chloride

Tony Nixon says:

I've been using Ferric Chloride for years now and it serves my purposes well. If you look at the method I use at http://www.bubblesoftonline.com/projects/pcb.html, you will find that the solution lasts a long time with excellent results. I've been using the same batch for years. I don't know if it's recylable, but all I know is, when it turns green, it's dead.

Robert A. LaBudde says:

You should be able to regenerate the solution electrolytically by using iron and a copper electrodes. Iron will oxidize from one electrode and copper will plate out on the other. So the copper electrode is the cathode and the iron one is the anode.

I would suggest connecting a ammeter in series and increasing the driving voltage up from zero until current starts flowing, then stop. The necessary voltage should only be ~ 1 V.

Too high a voltage and you'll electrolyze the water or hydrochloric acid present. So stop quick if you see any bubbles on the electrodes, and don't breathe any funny colored fumes!

The standard potential for the cell


        Fe | FeCl3 | CuCl2 | Cu

is -0.78 V, with the driving EMF cathode at the Fe electrode and the anode connected to the Cu electrode.

Unfortunately, it takes a lot of current to plate out the copper. A double-sided, 12-sq.in. board at 1 oz/sq.ft./side contains 4.7 g Cu. Therefore it takes 2.4 amp-hrs of current to plate it out!

Using iron nails as electrodes, you can drive about 0.1 A, so the process would take about 24 hrs for each circuit board. For totally spent etchant (i.e., 200 sq. in. per pint) the process could be up to 15x longer!

Obviously a larger surface electrode is needed to allow more current flow.

But now there's the problem of an efficient, high current, low voltage power supply.

Anyone got any ideas on how to efficiently generate 1 A @ 1 V?

No, but I can generate .997 V @ around 100 A using a Ordinary "Instant On" soldering iron like those sold by Weller or Radio Shack IE a 100 W soldering Iron. Take two HEAVY copper wires, and mount in place of the tip and connect to a 25 Amp or higher bridge rectifier. This should do the trick.+

By the way, a double-sided 3" x 4" pcb will use about $.20 of etchant, if you buy in large containers (e.g., 1/2 gal.), so this is more an intellectual exercise than a major cost-saving issue.

Muriatic acid and Hydrogen Peroxide

This is a /very/ fast and /very/ dangerious etchant. Always use outside or with very good ventilation and wearing protective gloves, goggles, long sleved shirt or jacket, etc...  lots of HCL fumes due to the exothermic reaction. Can foam, bubble, and even pop or spash.

1 ounce Muriatic acid from the hardware store
1 ounce BAQUACIL Oxidizer^ from pool supply store (27% H2O2) A chlorine-free liquid oxidizer of 27% specially-stabilized hydrogen peroxide used to clarify pool water by oxidizing organic compounds (swimmer waste).

As an example, this will remove all copper from a 2 inch by 4 inch, 1 ounce single sided board at room temperature in about 10 seconds! The down side is that because the material is removed at such a rapid rate, it can be very difficult to stop the etch before the protected traces are undercut.

Hydrochloric acid and Hydrogen Peroxide aka Cupric Chloride

Chuck Knight says: ^

"The recipe was simple. 2:1 ratio of H2O2 to HCL. The HCl was 20% concentration, in a toilet bowl cleaner called "The Works" that I purchased at WalMart for $0.94. The H2O2 was also from WalMart, from the pharmaceuticals section. Whatever they had...

The etchant works impossibly slow at first...threw in a sacrificial bit of copper wire, and let it dissolve all night. Once it turned from blue to emerald green, it worked beautifully for 4 boards. Took several hours to etch the boards. It did, however, turn into an ugly olive green that needed to be refreshed with a capful of H2O2, 3/4 of the way through the process."

Erik Knise advises: "At 20% concentration of HCL and 3% (standard over the counter pharmacy) H2O2 you should have a ratio of ~1:3 by weight (volume is about the same). So you would need 3 times as much H2O2 to HCL. The board should have etched within a few minutes."

DANGER: With 20% HCL (from a pool supply) and 30% H2O2 (hard to find, try a chemical supply store) mixed 2:1, once a little of the copper gets into the solution, the copper will literally foam off the board and the etching will be done in a minute! ^

Erik L. Knise's Cupric Chloride Echant calculator helps you design the perfect CuCl2 echant for your needs.

Other

Gary says:

I Electro-etch most boards. (Reverse Electroplating) Than just a bit of Ferric Chloride to finish them off at the end as  it is impossible to Electro-etch the last little bit. This Reduces my cost to almost Nothing.

I am using Old Sulphuric Battery Acid, Deluted 4 to 1 with water! This concentration, as well as spacing between electrodes and plate sizes, All determine current draw at any specific supply voltage! Most Other kinds of Acids may be used, but Sulphuric Acid is quite common. And usually available for Free from places that Recycle Car Batteries as they need to remove it before processing the lead. The Wire Lead soldered to the Circuit Board is an Enamaled Wire. The Enamal and Solder will protect this wire from being etched away!

Here I am Using a Power Supply, current limited to 4 amps, but this is a nominal current. The amount of current will determine how fast the etching goes. But it will also determine how hot the solution gets! Too hot is a problem! Additionally, too much current will result in poor etching. The Collector Plate (NEGATIVE) Electrode I am using is Stainless Steel, Because it stands up better over time! But almost any type of metal plate can be used! The PCB connects to the POSITIVE Wire.

It is useful to determine a good current level for etching with your particular solution. Once you have successfully etched a board, Divide the current by the area in Sq Inches. This will give you a Nominal Operating current "Per Sq Inch" of circuit board. You can now easily and relialably etch any size of board by multiplying its Sq Inches by this figure.

Reverse Plating can continue until most of the copper is removed from the board. As the copper gets etched away to almost nothing, the etching will automatically come to a stop. Once you are at this stage, you can now "Finish" the board in a "Ferric Chloride Solution".

See:
http://www3.telus.net/chemelec/Projects/Etching/Etching.htm

Also: Instead of using the "Tin Solution" to coat your boards, I would suggest you look into an "Electrolysis Nickel Solution". It does a MUCH BETTER JOB and Does Not Oxidize like the tin does. It is also a Good Electrical Conductor and adheres to the solder very well.

Nevr-Dull as a PCB cleaning aid seems to improve toner adhesion and a super clean surface with little effort.

Earl T. Hackett, Jr. says: "Many anti tarnish compounds contain amines that form very strong bonds to copper and often act as a base for adhering other materials. They are commonly used in photoresist compositions to enhance adhesion. Toner may (note I said may) actually stick better to an amine treated surface. Amines are readily removed in acidic etching systems so they shouldn't cause any problems in later processing steps."

Try electrocleaning PCB in say 5% sodium hydroxide, sodium carbonate or caustic dishwashing detergent. Dennis Hayes, during the very early days of Hayes Microsystem's was literally making modems on his dinning room table. He used to tin his boards, populate them with plastic dips and then run them through the dishwashing machine (On cold with NO heated dry...). Then he took them out and dryed them....

See also:

Archive:

Questions:

To retouch etch resist errors prior to etching, try a Tree House Studio #564815
fine tip Paint-Marker
+

Interested:


file: /Techref/pcbetch.htm, 17KB, , updated: 2013/1/30 12:37, local time: 2014/9/2 23:58,
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