COMMUNICATION EQUIPMENT AND APPARATUS # 16

Background

The manufacture of printed wiring boards (PWBs), the building blocks of the electronics industry, requires using substantial amounts of water and energy, and some hazardous chemicals that pose potential environmental and health risks. To facilitate the evaluation of alternative manufacturing technologies that reduce both environmental risks and production costs, EPA has entered into a partnership with the PWB industry through its Design for the Environment (DfE) Program. One of the goals of this cooperative effort (involving EPA, industry, trade associations, and public interest groups), is to generate and disseminate information on viable pollution prevention alternatives so that the industry can further explore cleaner manufacturing methods.

This case study focuses on the benefits of etchant regeneration systems, and how they can reduce the impact of etching processes on the environment while reducing costs.

This case study provides an overview of the different types of systems currently in use in the U.S. and is based on product literature, and on interviews with both equipment manufacturers and PWB manufacturers using the systems. The information is offered only as an introduction and has not been independently validate by EPA. For more information on any of these systems, contact the manufacturers at the numbers listed above.

Mention of trade names does not constitute endorsement or recommendation for use. Instead, the reader is encouraged to contact the individual companies for more information on their products.

Cleaner Production Principle

Recovery, Reuse and Recycle; New technology

Cleaner Production Application

In the process of making PWBs using the "subtractive" process, the circuit pattern is created by chemically etching copper from the unprotected (non-circuit) areas of the copper-coated panel, leaving circuit traces protected with photoresist. Etching can be accomplished with acids or bases, depending on the etch rate and the line width required. The ammoniacal etchants, either ammonium chloride or ammonium sulfate, are most commonly used. Cupric chloride is also used, even though it often requires chlorine gas, a significant health and environmental concern.

Approximately 60% of the copper on the board is removed in the typical etching process. As the copper content of the etchant increases, the etchant cannot effectively remove the copper from the board, and it is considered spent. The copper-saturated, spent etchant is stored in drums or a tank, and is ultimately shipped off-site for reclamation. Even in situations where the copper is recovered and the etchant is regenerated by the waste hauler, this waste stream may be an environmental hazard. Transportation of the spent etchant and its ultimate disposition may pose environmental risks and result in increased liability for the PWB facility. In many plants, the spent etchant is the largest waste stream generated, making it a prime pollution prevention candidate. The costs of managing spent etchants and the danger they pose to the environment can be reduced dramatically with an on-site regeneration system.

Ammoniacal etchant regeneration:

Alkaline etchants (ammonium chloride or ammonium sulfate) are the most commonly used types of etchants in PWB manufacturing. Without an etchant regeneration system, an optimal copper concentration is maintained by replacing spent etchant with fresh etch solution and shipping of the spent etchant off-site.

The Mecer System, manufactured by COGNIS, Inc., regenerates ammonium chloride, recycles rinse water, and recovers copper using a process of solvent extraction and electrowinning. The regeneration and recovery occurs in several stages:

Units are sized based on the total throughput of the etching line, best estimated by your current consumption rate of replenishes. Ten different size systems are available depending on the facility's annual replenisher volume, ranging from 14,300 gal/year to 380,000 gal/year.

The Elo-Chem Alkaline Regeneration Module and Copper Recovery System distributed by Atotech, regenerates ammonium sulfate and recovers copper in a closed-loop system. Although using ammonium sulfate allows direct electrolysis of the etchant, it also has a slower etch rate than ammonium chloride. The Elo-chem system consists of two separate regeneration circuits: an etchant recycling module and a copper recovery module. Etchant is regenerated utilizing atmospheric oxygen and ammonia to restore the copper in the spent etchant to the ionic form needed for etching. A portion of the solution is guided to the electrolytic cell, where copper is deposited on the cathodes. After electrolytic deposition of the copper is completed, the copper can be pulled off of the cathodes as a copper sheet.

The system works with a wide range of production capacities. The same equipment is used for all size facilities, and multiple plating cells are added to accommodate facilities with larger production capacities.

Cupric Chloride Regeneration:

Many PWB manufacturers use a cupric chloride etchant to achieve fine line width etching, although it typically has a slower etch rate than ammonium chloride. Without an etchant regeneration system, manufacturers would typically purchase bulk chemicals to blend etchant and spent etchant would be shipped off-site. With etchant regeneration and recovery systems, saleable copper is recovered from the spent etchant and off-site shipments f spent etchant are eliminated. The types of regeneration equipment available include the FSL system, which recovers copper and regenerates etchant; and the Chemcut system, which regenerates etchant but does not recover copper.

The FSL Electrolytic Regeneration system, distributed by Finishing Services Limited, is a closed-loop system that regenerates etchant and plates out the copper.

The smallest FSL Regeneration system available is a module that removes 2.2 pound of copper per hour; by joining these modules together, FSL can supply a system large enough to accommodate hundreds of pounds of copper per hour. As system capacity increases, however, so does the size of the system.

Combined system - cupric chloride/ammonium chloride:

Many PWB manufacturers use both cupric chloride and ammoniacal etchants. These sites incur the costs associated with off-site shipments of spent etchant and chemical purchases for both types of etchant. However, they can also realize the benefits from etchant regeneration and copper recovery from both types of systems. These manufacturers are in a position where they can evaluate the benefits of purchasing either two individual etchant regeneration systems, or a combined cupric chloride/ammoniacal etchant regeneration and copper recovery system.

ARS, which distributes ARS Resource Recovery, has recently installed its first integrated etchant regeneration and copper recovery system at one of the largest PWB manufacturing facilities in the country. At start-up, the system will allow this facility to process, on-site, its flows of cupric chloride spent etchant and ammoniacal spent etchant. In the future the facility plans to use the system for recovery of copper from all copper dumps in the facility.

The initial system installation described here was designed for a large, high volume PWB manufacturer; however, ARS is currently developing the integrated regeneration technology to meet the needs of mid-sized companies.

Environmental and Economic Benefits

The benefits of etchant regeneration and copper recovery included:

Although the technology may not be suitable for all operations, on-site etchant regeneration systems have successfully prevented pollution both in very small, prototype board shops, and in some of the highest volume PWB manufacturers in the country.

Ammoniacal Etchant Regeneration:

Mecer System :

Elo-Chem System

Both large and small facilities have installed the Elo-chem system for etchant regeneration and recovery. The average copper recovery capacity of the system is 5.5 lb/hour, with a maximum hourly capacity of 6.6 lb. One customer who runs a prototype board shop (using fewer than 10,000 gallons of etchant/year), describes this as the "ideal" system for their operation. They expect the system can eliminate the time and resources associated with shipping spent etchant off-site, reduce the space required for storage of fresh and spent etchant, decrease chemical purchase costs, eliminate safety issues associated with handling drums, and improve etching process control. Ammonia gas, a proprietary rate accelerator (added at 0.25 liter/plating hour), and small quantities of ammonium sulfate crystals (from an industrial chemical supplier) are needed to operate the system; actual quantities required depend on the carry-over losses.

Cupric chloride regeneration:

 FSL System: