Substitutes for Ozone Layer-Depleting Solvents in the Printed Circuit Board Industry

Fact Sheet #7
July, 1992


What's New

Newsletter

Free Offers

Order Forms


Automotive

Dry Cleaning
Wet Cleaning

Electronics

At Home

Labs

Marinas

Metal Finishing

Metal Working

Paints and
Coatings

Printing

Recycling

Solvents

New scientific information suggests that ozone-depleting chemicals are causing a thinning of the ozone layer over the northern hemisphere as well as Antarctica. This information prompted the U.S. government to accelerate the phase-out of ozone-depleting chemical production from the year 2000 to the year 1995.


Many industrial cleaning processes have relied heavily on the use of chlorinated solvents, specifically 1,1,1- trichloroethane (TCA) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113). They are regulated as hazardous wastes. These chlorinated solvents also have been identified as ozone-depleting chemicals and are being phased out under the Clean Air Act Amendments of 1990. President Bush has requested that the phase-out schedule be accelerated under terms set forth by Section 606 of the Clean Air Act Amendments. Rising tax costs and the decreasing availability of these solvents is prompting manufacturers, especially those in the printed circuit board industry, to seek alternatives.

At this time, there is no common or simple substitute for the wide variety of solvent uses. This is despite the fact that a substantial amount of money and time have been invested in research to find alternatives to chlorinated solvents. There are, however, a number of general methods that have been found to work well for certain applications.

The number of variables involved with different cleaning systems requires that each application be investigated and studied for a compatible substitute. Issues such as cleaning effectiveness, toxicity, flammability, material compatibility, and cost need to be addressed when searching for a solvent alternative.

Historically, benign or non-aggressive fluxes have been used in the circuit board assembly process. Advances in surface mounted devices and more densely "wired" circuit boards, have caused a demand for more aggressive fluxes. The same level of solderability generated by the previously used fluxes must be maintained by the more aggressive fluxes. The corrosive nature of these fluxes is putting a higher demand on cleaning systems to effectively remove them after the soldering process is complete. The following is a brief description of four alternatives to chlorinated solvent use for printed circuit boards. These are: aqueous cleaning, water soluble and low solids fluxes, inert gas soldering and carbon dioxide.

Aqueous Cleaning

Aqueous cleaning systems can be used for most electronic circuit boards, including both surface mount and through hole technologies. In general, aqueous cleaning systems consist of a wash cycle, a rinse cycle, followed by one or more drying cycles.

Aqueous cleaning solutions are water based and can contain a combination of water conditioners, alkalinity builders, and a variety of organic surfactants. The alkalinity builders help neutralize the acidic nature of applied fluxes. The surfactants displace particulates from surfaces that are being cleaned. Tap water is usually sufficient for the initial stages of aqueous cleaning. Rinse stages should use deionized water. Ions such as calcium and magnesium present in the water during the rinse stages can cause corrosion problems.

Currently there are no industry standard levels of water deionization. Through experimentation it is possible to find an adequate deionization level for a particular application. Agitation during the wash cycle of aqueous cleaning systems dramatically increases cleaning efficiency. Agitation can be achieved with the use of ultrasonics, mechanical agitation, or jetting actions. These processes promote the loosening of particulates and increase the effectiveness of the solution detergents.

There can be many rinse tank arrangements for an aqueous cleaning system, but designs that incorporate counter current rinsing will reduce water use.

For example, if a cleaning system is using three rinse tanks, overflow from the final rinse tank is fed into the intermediate rinse tank. At the same time, overflow from the intermediate tank is fed into the first rinse tank. System make-up water is supplied to the final rinse tank and overflow from the first rinse tank is disposed of in an environmentally sound manner.

Along with the use of automated cleaning systems in production lines, manual "wash stations" can be used to clean parts such as reflow soldering masks or other contaminated tools. An elaborate "wash station" set-up is not necessary. One might simply consist of a solution, a rinse tank, and a brush.

Aqueous cleaning offers an effective alternative for most electronic printed circuit board cleaning but does have disadvantages. When using water, it is important that electronic devices are sufficiently sealed to prevent leakage that would render the device useless. In addition, drying cycles are required to remove all moisture from the cleaned boards.

Because particulates removed from the circuit boards are present in the wash and rinse baths, it is necessary for the baths to be processed to remove the contaminants. Certain types of contaminants present in the cleaning baths may render them a hazardous waste. These materials include heavy metals and some organic chemicals.

As one example, Digital Equipment Corporation was using just under a million pounds of CFCs in 1988, in its manufacturing process. In 1992, the company uses less than 85,000 pounds a year. This is partly a result of Digital's Microdroplet Module Cleaning Process which is used to clean fine-pitch surface-mount circuit boards. Digital defined the angle of impingement of water and the water droplet size as the key parameters that make the aqueous cleaning process effective.

Water Soluble and Low Solids Fluxes

Cleaning requirements can be dramatically changed with the use of different fluxes. Water soluble fluxes, usually of a very aggressive nature, can be cleaned with deionized water and applied in similar methods as with the above mentioned aqueous cleaning solutions. These types of fluxes produce excellent solderability conditions. However, proper care should be taken to ensure that the fluxes are adequately removed from the circuit boards to avoid corrosion. Water rinses have disadvantages similar to aqueous cleaning systems.

The use of low solids fluxes (LSFs) is gaining wider acceptance in the printed circuit board industry. Their most attractive asset is that they eliminate the need for cleaning. When the circuit board undergoes the soldering process the flux is consumed. Not only does this remove a manufacturing step for cleaning, it also eliminates the use of cleaning solvents and solutions altogether and reduces the use of flux materials. LSFs are usually used with through hole technologies and require that flux application be controlled for deposition consistency.

Consistently controlled LSF deposition ensures minimal use of flux material and reduces post soldering flux residues. AT&T Bell Laboratories has conducted long-term corrosion tests on circuit boards using LSFs. They have found that excessive flux residues can cause corrosion effects that lead to current leakage.

To minimize flux residues, Bell Laboratories developed a low solids fluxer that consistently controls flux deposition rates. These rates are set by the machine operator, through the use of an air assisted self-cleaning airless spray nozzle. Use of this machine results in a repeatable, uniform application of flux to the board and is not limited to the exclusive use of an LSF. AT&T's Columbus facility has used LSFs in its printed circuit board manufacturing process with successful results.

The controlled application of LSF produces reliable circuit boards without the use of ozone-depleting solvents, reducing hazardous waste management costs. Savings include the elimination of one or more manufacturing steps and reduced uses of flux material. Cost savings at AT&T's Columbus facility are estimated at approximately $145,000 per year. Several no-clean fluxes are available on the market. These fluxes contain 1-5% nonvolatile material by weight. This is considerably less than the conventional fluxes that typically contain 25-35% nonvolatile solids by weight. Extensive research by AT&T has shown that the use of these LSFs without special application methods may cause problems in product reliability.

An initial capital investment associated with application machinery is one of the few disadvantages associated with the use of LSFs. In addition, LSFs currently are not allowed under military specifications, but an effort is being made to address this problem.

Inert Gas Soldering

Inert gas soldering uses an inert gas environment for soldering to prevent contamination during the soldering process. Inert gas soldering units do not use a flux but "shield" the area to be soldered with a blanket of nitrogen or other inert gas. The gas blanket prevents particulates or other contaminants such as metal oxides to decrease the solderability of the product. The major drawback to using inert gas soldering is the high capital investment of soldering equipment.

Dry Ice Blasting

One recently developed cleaning technology is similar to grit blasting. It uses small, uniform pellets of solid carbon dioxide as a blasting medium. The system's cleaning ability is due to the pellets' kinetic energy and thermal effects. The pellets disintegrate and release into the atmosphere leaving only the removed contaminant for disposal. Process parameters such as pellet size, hardness and quantity are easily controlled by the operator. This accommodates a wide range of application needs.

The system has proven effective for cleaning unpopulated printed circuit boards, test fixtures and deflashing molded plastic parts. The cleaning process is inert and therefore nonconductive, making it ideal for electrical and electronic applications. Research is being conducted on flux removal of populated boards to address the potential problems of integrated circuit shadowing and electrostatic discharges.

Solvent Containing Products

The majority of ozone-depleting solvents are associated with cleaning processes, but these chemicals are also used in products such as surface mount adhesives and component coatings. Ask your vendor if solvent-free products are available. If they are not offered with your particular vendor, check with a different one.

Several product vendors are attempting to produce full product lines of solvent-free surface adhesives, coatings, and encapsulants. Using products such as these can further reduce the overall use of ozone- depleting solvents associated with the printed circuit board industry.

Conclusion

Effective technologies and methods are being developed that will replace ozone-depleting solvents. In 1991, Northern Telecom eliminated its use of CFC-113 by adopting new soldering processes which make cleaning easier. Just two years earlier at its Bramalea plant, Northern Telecom was using 59 tons of CFC-containing solvent.

Companies should actively seek these technologies and implement them. Smaller companies that cannot afford extensive research resources can request assistance from companies that have already incorporated such technologies. They can also ask their vendors and state technical assistance programs if they offer alternatives to chlorinated cleaning solvents and toxic and hazardous solvents. Alternative technologies do exist. Compatible uses of these technologies for certain applications need to be examined until desired results are achieved. Some suppliers and vendors would be interested in helping with this type of "test market." With the phase-out deadline approaching fast, and the costs associated with chlorinated solvent use rising, cleaning alternatives cannot be incorporated too soon.


Sources:

Alternative Technology

Archie Kontos
AT&T
Engineering Research Center
P. O. Box 900
Princeton, NJ 08540
(609) 639-2232

Bob Carter. 1992. Solvents- The Alternatives. Waste Reduction Resource Center For the Southeast, Raleigh, NC 27609

Environmental Program Office, City of Irvine. July 1991. CFC Alternatives. Irvine, CA

Raymond Pickering
Digital Equipment Corporation
500 Civic Center Drive
Augusta, ME 04330-9417
(207) 623-6511

U. S. EPA. 1991. Aqueous and Semi-Aqueous Alternatives for CFC-113 and Methyl Chloroform Cleaning of Printed Circuit Board Assemblies. EPA 400/1-91/016. Air and Radiation, Washington, D.C.


Chemical Substitutes

Du Bois Chemicals Inc.
225 East 5th Street, Chemed Ctr.
Cincinnati, OH 45202
(513) 762-6000

DuPont
14 TW Alexander Drive
Research Triangle Park,
NC 27709
(919) 248-5076

Kelly Stevens
Hughes Environmental Systems
Hughes Aircraft Company
(800) 262-4374

Man-Gill Chemical
23000 St. Clair Avenue
Cleveland, OH 44117
(216) 486-5300

Maher Tadros
Martin Marietta Corp.
1450 S. Rolling Road
Baltimore, MD 21227
(301) 247-0700

Michael E. Hayes
Petroferm Inc.
5400 First Coast Highway
Fernandina Beach, FL 32034
(904) 261-8286


Dry Ice Blasting

Alpheus Cleaning Technologies Corp.
Ohio Distributor-Stanley Industries
Jay Cusick
19120 Cranwood Parkway
Cleveland, OH 44128
(216) 475-5000

Cold Jet, Inc.
455 Wards Corner Rd
Loveland, OH 45140
(513) 831-3211

John Whalen
Waste Minimization & Containment Services Inc.,
2140 Scranton Rd.
Cleveland, OH 44113
(216) 696-8797


General Information

G. M. Wenger, L. A. Guth and D. A. Dickinson. March 1990. Advances in Cleaning of Surface Mount Assemblies. Circuit World. v.16 (#3).

Katy Wolf. 1992. An analysis of Alternatives to Ozone Depleting Solvents in Cleaning Applications. Pollution Prevention Review, Vol. 2, No. 1, Spring 1992.

Mitchell Kennedy. 1992. The Solvents Bazaar: A Cooperative Effort Between Government and Industry. The Office of Technical Assistance for Toxics Use Reduction (Executive Office of Environmental Affairs), Boston, MA

Richard Quenneville
Industrial Hygienist
Northern Telecom Canada Ltd.
8200 Dixie Road
Brampton, Ontario L6V 2M6
(416) 452-4414

Source Reduction Research Partnership (Metropolitan Water District of Southern California, Environmental Defense Fund). 1991. Source Reduction of Chlorinated Solvents: Electronic Products Manufacture. Alternative Technology Division, California Department of Toxic Substances Control, Sacramento, CA

U. S. EPA. 1991. Achievements in Source Reduction and Recycling for Ten Industries in the United States. EPA/600/2-91/051. U. S. EPA, Office of Research and Development, Washington, D. C.

U. S. EPA. 1990. Manual of Practices to Reduce and Eliminate CFC-113 Use in the Electronics Industry. EPA 400/3-90-003. Air and Radiation, Washington, D.C.

Waste Reduction Assistance Program. 1992. Ozone Depletion: U. S. Picks Up Pace. WRAP Sheet, Vol. 2 No. 1, Spring 1992. The University of Tennessee's Center for Industrial Services, Knoxville, TN


LSFs

Barbara C. Thompson and
Girish D. Parikh
AT&T Manufacturing Division
6200 East Broad St
Columbus, OH 43213
(614) 860-5594

Emerson & Cuming
77 Dragon Ct
Woburn, MA 01888
(800) 832-4929

Technical Assistance

Cleveland Advanced Manufacturing Program (CAMP),
17325 Euclid Ave.
Cleveland, OH 44112
(216) 531-8359

Industry Cooperative for Ozone Layer Protection (ICOLP)
1440 New York Ave., SW.,
Suite 300
Washington, D.C. 20005
(202) 737-1419

Institute of Advanced Manufacturing Sciences, Inc.
1111 Edison Dr
Cincinnati, OH 45216
(513) 948-2009
(800) 345-4482

Office of Pollution Prevention
Ohio Environmental Protection Agency
P.O. Box 1049
Columbus, Ohio 43216-1049
Phone (614) 644-3469
Fax (614) 644-2807

This is the 7th in a series of fact sheets Ohio EPA has prepared on pollution prevention. For printed copies of this or other pollution prevention publications distributed by the Ohio Environmental Protection Agency, Office of Pollution Prevention, please call the Office of Pollution Prevention at (614) 644-3469.

A printed copy of the Office of Pollution Prevention publications distribution list, "Pollution Prevention Information Available from Ohio EPA", may also be ordered by calling (614) 644-3469.

Office of Pollution Prevention
Ohio Environmental Protection Agency
P.O. Box 1049
Columbus, Ohio 43216-1049
Phone (614) 644-3469
Fax (614) 644-2807


Back to the Ohio EPA Home Page
Back to the Ohio EPA, Office of Pollution Prevention Home Page