Electroplating metal connections


People have suggested that you cannot electro deposit silver directly onto Lead Dioxide and that it must be sprayed on or painted on.
You may be able to use an "electroless" silver plating tank to plate silver onto the PbO2. This is a plating tank that does not use plating current to but the silver onto the object to be plated. The silver deposits onto the object of its own accord. It is not the same as silvering mirrors, where a similar thing happens. The silver baths that are used for silvering mirrors will only put on a very thin deposit of silver and then will STOP plating. The true electroless plating tanks will go on depositing silver and build up a layer of silver of the required thickness that you want. Be very careful with silver electroless plating baths. If they are left lying around after the plating job is complete, very explosive compounds can form and will cause an explosion as soon as you touch the container. The following electroless silver plating baths are taken from US Patent No. 3,318,794. See http://ie.espacenet.com/ for the patent.
In the patent they discuss silvering the inside of a hollow cylindrical powdered Lead Dioxide/plastic polymer anode with silver using the following process:
Solution A:
15 g. silver nitrate in 1500 ml solution with enough ammonia so that the final pH is 10.

Solution B:
1 gram silver nitrate and 0.83 grams Rochelle salt in 500 ml water, boiled for 20 minutes and filtered

The anode cavity is washed with 5% NaOH and then filled with 460 ml A and 90 ml B

Electrolysis is carried out with a silver electrode hanging in the center (recall that this is plating the inside of a hollow PbO2 cylinder). The silver is plated on the Lead Dioxide until the process ceases, then a new solution is prepared and used to plated, etc. several times until a decent layer is deposited.
After this, copper is plated over the silver using with a bath made of 200g/L CuSO4 and 50g/L H2SO4.

Plating copper

Copper sulfate/sulfuric acid is the preferred copper plating bath in the electronics industry. Copper concentration in the 12-18 g/L range, sulfuric acid in the 200-250 g/L range and chloride in the 30-60 ppm range. Levelling/carrier agent such as 2,000 polyethylene glycol and brightening agent such as an alkyl sulfonate both in the ppb/ppm range are essential for macro and micro level grain refining to enhance the hardness and tensile strength of the deposit. Without these additives the deposit will be matt in appearance and have both lower ductility and be more susceptible to cracking under thermal stress.
The proper control of these components is most easily determined using a Hull cell which allows you to visually compare the appearance of the deposit over a range of current densities. This is accomplished by angling the cathode at 45 degrees WRT the anode in a small plating cell (I can't recall the dimensions off the top off my head). These later two components are typically proprietary in nature and sold by electroplating chemical specialists such as Lea Ronal/Shipley, MacDermid Chemical, Atotech USA.
The cathode is the piece that is being plated the anode in this case would be a copper bar or basket with copper balls or chips.
The bath must be aerated at the cathode to prevent burning (soft powdery copper deposition). The cathodic current density is typically in the 12 to 18 ASF (13 to 19mA/cm^2) range for the Cu/H2SO4 ratio outlined above.
Regarding the chloride...it's use pertains to a copper sulfate plating bath. The purpose is to aid in uniform dissolution of the copper anode as the cupric ions are deposited onto the piece your plating. Chloride becomes a component of the black film that forms on the anode (along with the organic additives). The film forms as the copper in the anode dissolves to replace the cupric ions as the plate onto the cathode (your product). It is usually added in the form of HCl but NaCl works as well.

Copper plating by TB

Purifying sterling silver

Dissolve your sterling silver in nitric acid; a bit of heat will help if your acid is dilute. Next, precipitate the silver as the chloride, AgCl, by adding an excess of NaCl solution. Wash your precipitate and then reduce it to metallic silver by one of the following methods:

1) Add an excess of NaOH solution and heat to boiling/ nearly boiling. Add either glucose (dextrose) or formaldehyde solution, a little at a time, until all the AgCl is reduced to metallic silver. (The resultant silver powder is grey. not shiny) This method only takes less than an hour.

2)Add some pieces of zinc to your AgCl under water. The zinc will slowly reduce the AgCl to silver metal. The excess zinc can be dissolved in HCl. This method takes a few days.

3) Dry your silver chloride and intimately mix it with an excess of Na2CO3 (soda ash). Heat this mixture with a propane torch (this is normally done on a block of charcoal) until the silver melts to form a button of pure silver.

I prefer the first method as I have used it on several occasions in the past. I have never tried this, but you might be able to make your own conductive epoxy by adding the silver powder obtained in methods (1) or (2) to some normal (not 5 minute!) epoxy. The idea is to use the epoxy to bond some copper strip to the electrode. This will only require a small amount of epoxy. It might also work if you add graphite powder rather than silver although I expect the resistance to be higher.

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