Grantee Research Project Results
Final Report: Etchant Recovery System
EPA Contract Number: EPD05019Title: Etchant Recovery System
Investigators: Sallo, Jerome S.
Small Business: Republic Anodes Fabricators, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2005 through August 31, 2005
Project Amount: $68,200
RFA: Small Business Innovation Research (SBIR) - Phase I (2005) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Hazardous Waste/Remediation , SBIR - Waste
Description:
testIn the manufacture of printed circuit boards (PCBs), etchants are used to dissolve unwanted copper. The most commonly used etching solutions are cupric chloride and ammoniacal etchant. The copper ion content of the etchant is maintained at a constant value, pH is controlled and a “bleed and feed” system is used to remove excess etchant formed as the system runs. This excess etchant is stored and eventually hauled away as a hazardous waste. In the case of cupric chloride, the system is very high in hydrochloric acid. The ammoniacal etchant is very high in ammonia content.
Each system requires reoxidation of the etchant in order to maintain a constant etch rate. The oxidants used, such as chlorine gas, are hazardous and may be accidentally released into the environment. The ammoniacal etchant is reoxidized by air and, therefore, must be maintained at a very high pH to increase the rate of air oxidation. This increases the rate of evolution of ammonia gas.
Republic Anode Fabricators Inc. (RAF) has previously developed a commercial device for regenerating ferric chloride etchant. Although rarely used in the printed circuitry industry, ferric chloride is widely used in photochemical machining. The existing device uses electrochemical technology. In operation, ferrous ion is converted to metallic iron at the cathode and ferrous ion is oxidized to ferric ion at the anode. Thus, the etched metal is recovered as a nonhazardous salable scrap metal and the spent etchant is regenerated at the anode. The metal is deposited non-adherently on disc-shaped cathodes, and continuously removed mechanically so that it cannot redissolve in the etchant. This forms a closed-loop system and eliminates the need for oxidant and disposing of hazardous materials.
The successful operation of the unit depends upon the presence of ferrous ion at the anode. In the absence of ferrous ions, chlorine gas will be liberated. Efforts to utilize this technology on either cupric chloride or ammoniacal etchant result in substantial chlorine gas liberation. Even so, when cupric chloride or ammoniacal etchants are run, the present device will produce a copper powder at the cathode that is nonadherent and easily removed.
The purpose of this Phase I research program was to provide the PCB industry with a means of utilizing standard etchants with the following improvements:
- Hazardous spent etchant eliminated by use of a closed-loop system
- Use of hazardous oxidants replaced by clean, safe electrical power
- Lower pH for ammoniacal etchant to minimize ammonia evolution
- Lower cost of operation
- Automatic recovery of the etched copper as a metallic powder
- No membranes to separate the anolyte and catholyte
- Potential for capacity suitable for PCB production needs, 2 to 6 pounds of copper per hour, at reasonable voltage (i.e.,10 to 12 volts)
RAF planned to accomplish this by modifying the existing ferric chloride device so as to capture the evolved chlorine gas and cause it to react with the spent etchant. This must be accomplished without liberating any chlorine gas into the environment.
Summary/Accomplishments (Outputs/Outcomes):
A sealed plating cell was designed based upon the existing ferric chloride system, but on a greatly diminished scale. The working system includes a small (6 inch diameter) disc as the cathode and two anodes. The cathode rotates to facilitate removal of the deposited copper. The rotating shaft is connected to the rectifier by means of a commutator. The initial cell did not have scrapers for automatic copper removal. The lid of the cell is sealed to the body of the cell with O rings, and the inlet and outlet tubes are sealed with adhesives. There are pumps to circulate the spent etchant through the cell from a holding tank. A 55-gallon drum of spent cupric chloride etchant from an actual etching process was obtained for experimental purposes.
The major design effort was the problem of containing the chlorine gas within the system and causing it to completely react with the spent etchant. To ensure that this was accomplished, and to maintain the safety of the environment, a chlorine detector capable of detecting 0.5 parts per million of chlorine was used. In order to provide a sufficient interaction between the evolved chlorine gas and the spent etchant, a long tube was designed that would be filled with flowing spent etchant. The evolved chlorine along with spent etchant was introduced into the bottom of this tube and allowed to flow to the top along with the circulating spent etchant.
Some of the features of the final cell design were not compatible with the use of ammoniacal etchant. Therefore, the research was limited to experiments with cupric chloride etchant.
The initial runs with this system were marginally successful. At 25 amperes of current, the system could be run for 5 minutes before chlorine began to escape. The chlorine escape took place where the spent solution returned to the holding tank after passing through the long tube. When the experiment was terminated by turning off the rectifier, the chlorine escape ended. The absence of chlorine when the system is not operating is a major safety feature. At 50 amperes, chlorine escape began after only 2 minutes. During these experiments, a considerable amount of copper was deposited on the cathode disc, and the oxidation reduction potential (ORP) of the spent etchant solution rose, indicating that the spent etchant is undergoing regeneration, as expected.
A review of the data convinced RAF of the need to provide more dwell time between the evolved chlorine and the spent etchant. Several methods were considered, including the addition of glass wool or glass beads, and lengthening the tube by adding a spiral or circuitous path for the chlorine escape. Finally, a section of glass wool was added to increase the surface area where the initial reaction of the chlorine and spent etchant first occurs.
Experiments with this arrangement were very successful. After running at lower currents as trials, several runs were made at 70 amperes; this was RAF’s targeted current density. Each run was terminated after 8 minutes to prevent the copper accumulated on the cathode from becoming thick enough to contact the anode. There was no escape of chlorine. Chlorine gas evolution could be visually observed in the cell and the copper accumulation on the cathode. After the cell was opened following the run, a substantial amount of copper was collected. The copper was sent out for analysis, and various lots ran between 99.8 percent copper to 99.9 percent copper. The ORP rose substantially during each run, indicating successful regeneration of the spent etchant.
Following this successful verification of the concept, RAF decided to make quantitative measurements. This required the continuous removal of the copper powder from the cathode disc while the cell was in operation. Scrapers were fabricated and attached to the cell adjacent to the disc to remove the copper. Since the deposited copper is very heavy and sludge-like, a technique for manually pulsing water onto the scrapers was added. This permitted the flow of copper from the scraper surface into the receiving area, and allowed RAF to make longer runs and collect most of the copper produced. RAF’s quantitative collection experiment showed a minimum of 90 percent efficiency in copper collection compared to theoretical possibility (Coulomb’s Law). RAF was unable to quantify the regeneration of the etchant at the anode other than by ORP measurement. Since there was no chlorine escape, it is known that all of the chlorine produced was consumed in etchant regeneration. While RAF does not know the efficiency of chlorine generation at the anode, it should be very high because the next possible reaction (water to oxygen) occurs at much higher voltage.
Subsequent to these experiments, RAF was able to find techniques for better mixing of the chlorine gas and the spent etchant. Using the improved methodology, RAF was able to operate successfully without the glass wool or the long etchant-filled tube. Chlorine gas did not escape from the system and the 90 percent efficiency for copper collection was confirmed. RAF now has this unit as a working system to demonstrate the concept.
Conclusions:
RAF has proven the technical feasibility of the concept. The firm has built an experimental cell that regenerates spent cupric chloride etchant without liberation of chlorine gas into the atmosphere at a level of 0.5 parts per million of air. Copper has been recovered at 99.8 percent purity at 90 percent efficiency. RAF has a working model of the system. The firm believes that the concept is ready to be designed and expanded into a commercial etchant regeneration system.
The experiments have shown the system to be capable of meeting the original goals of:
- Hazardous spent etchant eliminated by use of a closed-loop system
- Use of hazardous oxidants replaced by clean, safe electrical power
- Lower cost of operation
- Automatic recovery of the etched copper as a metallic powder
- No membranes to separate the anolyte and catholyte
- Potential for capacity suitable for PCB production needs, 2 to 6 pounds of copper per hour, at reasonable voltage (i.e.,10 to 12 volts)
The system RAF has developed will not operate with ammoniacal etchant. RAF has failed to achieve that original goal.
RAF has contacted a number of potential users of the concept, and has received many positive responses. In particular, one major corporation has expressed interest in working with RAF in the development and prototype phases. This company has offered to allow RAF to attach its experimental cell to that company’s operating etcher. That company’s system uses chlorine gas to regenerate the etchant. RAF’s system would provide the chlorine gas in situ, and avoid the safety issues involved in the storage of liquid chlorine under pressure. The existing system does not recover the copper and requires the hauling away of hazardous wastes.
In addition, a market survey was done for RAF by Foresight. Its report validated RAF’s concepts. All of the outside experts and users contacted by Foresight confirmed the need for this concept in the industry. Foresight’s report indicates that the sales price of a production unit is compatible with RAF’s initial estimates of the production costs of the unit. Foresight has also indicated an appreciable market size for the units.
Supplemental Keywords:
printed circuit boards, etchant, ammoniacal etchant, hazardous waste, ferric chloride, ferrous ion, chlorine gas, cupric chloride, photochemical machining, sealed plating cell, oxidation reduction potential, glass wool, anode, cathode, anolyte, catholyte, scraper, EPA, small business, SBIR,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, TREATMENT/CONTROL, Sustainable Industry/Business, POLLUTION PREVENTION, waste reduction, Environmental Chemistry, Sustainable Environment, Technology, Technology for Sustainable Environment, Hazardous Waste, Environmental Engineering, Hazardous, environmentally benign manufacturing, waste minimization, clean technologies, cleaner production, environmentally conscious manufacturing, recovery, environmental sustainability, etching, printed circuit boards, alternative materials, closed loop recycling, environmentally begin etchants, copper, environmentally benign alternative, ammonia etchant alternativesSBIR Phase II:
Etchant Recovery SystemThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.