Russell wrote:
> twb8899 wrote:
>
>>Adam's comments are correct concerning the use of a sulfuric acid
>>based copper plating system. It will work even better if
>>a "brightner" chemistry is added to the tank. This helps to level out
>>the plating and increase the "throwing power" which is very important
>>when plating in the holes. Do a search on "throwing power" to learn
>>more about this.
>>
>>When plating large flat areas the center of the panel will receive
>>the minimum amount of plating while the edges and corners will get
>>the most. Brightner chemistry helps to level this out and also
>>increase the efficiency through the holes. What is needed is a 1:1
>>thickness ratio between the hole wall and surface thickness and this
>>is almost never achived but you can get very close.
>>
>>The copper anodes should contain a small amount of phosphorus to
>>plate properly in an acid copper tank. These anodes will be
>>marked "CU-PHOS"...
>
>
> What is the phosphorous for?
> I've found that hard-drawn copper shim etches much more difficult
> in FeCl than the copper on circuit boards. Why? (i've tried cleaning
> any preservatives off first)
>
I've read that grain structure has an effect copper etching speed. The copper on
PCBs is made from electroplated foil over stainless steel drums is then hot
rolled to the epoxy sheet. My guess is they want softest copper.
The phosphorous in copper anodes is to produce correct erosion of the anodes. I
think its quite complicated, but when using a typical PCB plating bath
containing brightening additives, and high acid/copper ratio then if you use
normal copper anode they tend to erode with loose film of copper particles. The
bath soon builds up a sediment of copper power. However with using copper with
0.05% phosphorous (anodes for acid copper plating) then a dark, almost black,
film develops over the anodes and does not produce powdery copper. The anodes
are "bagged" with a polypropylene fabric to minimize solution flow and upsetting
the delicate black film on the copper anodes.
When I first started doing experiments with copper plating I used much lower
acid/copper ratio (no additives) as this was described in most old texts. Using
plain copper anodes didn't produce even a tenth as much power as they did with
the PCB bath above. Some copper powder was released but not enough be a big
problem. The PCB plating bath is superior to standard plating bath because of
the improved "throwing power" as Tom explained. Without additives you will have
a hard time trying to get uniform plating. Also without additives, the deposts
get very rough with increasing plating thickness.