Etchant Regeneration and Copper Recovery System:
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Link to Cemco article published on www.PCB007.com
dated 11 March 2008 entitled
The Cemco Etchant 'Regen' System uses a specialised Electrolytic Cell enabling Acidic Cupric Chloride Etchant to be 'regenerated' whilst recovering the copper etched from the panel surface.
Cemco manufacture Regen systems in a range of sizes. They are built as 2kg (4.4 lb)/per hour cell modules. This refers to the recovery rate of copper per hour. Modules can grow in size to a maximum of 10 kg (22 lb)/per hour. Thereafter multiples of modules can be used in series with one another to suit any size production
RECOVERY OF COPPER
The equation for the Etching Process is:-
Cu + Cu Cl2 2 CuCl
Cu Cl2 being active Acidic
As the Copper dissolves the effectiveness of the solution falls dramatically and it must be regenerated. The traditional way of doing this is to oxidise the cuprous ion produced with Acidified Hydrogen Peroxide. During this process the volume of the solution increases steadily. The etching module will constantly produce spent chemical during the period of operation due to the necessity to re-oxidise the etching bath.
The excess or spent etchant is a hazardous waste which is becoming increasingly more expensive to remove. Spent solution is normally precipitated as Copper Oxide and discarded for landfill.
The original proposal for
recovering the copper in a high quality form came from EA Technology
Ltd. Using an electrolytic technique
involving a divided cell, simultaneous regeneration of the etching
solution and recovery of the unwanted Copper is made possible.
Special membranes act as Cell dividers
allowing current to be passed between the electrodes whilst keeping the
Anolyte and Catholyte solutions apart.
Copper concentrations are maintained using
synchronous metering pumps. Recovered Copper is collected at the cathode
as pure Dendritic flakes.
HOW DOES THE REGENERATION SYSTEM WORK?
Etchant is pumped in a closed loop between the etch module and Electrolytic Cell in high volume. A Redox Oxidation Reduction Potential controller monitors the condition of this fluid loop. The probe will activate the Electrolytic Cell dependent on the volume of work being processed through the etch module.
When activated, etchant is re-oxidised at the anodes to yield an active high O.R.P. etchant, whilst copper is being deposited at the cathodes from where it is scraped and settles in the copper collection area. The Anodes and Cathodes are separated by a semi permeable membrane which allows current transfer between the electrodes. The solution used at the Cathode is also Acidic Cupric Chloride but in a reduced state. The Electrolytic Reaction ceases when the Redox Potential reaches its required value.
Due to the high turnover rate of the etchant bath, the reaction time to chemical change is significantly faster than conventional additive dosing systems.