Operating Features - Guide to Cleaner
The wide variety of non-cyanide strippers makes it difficult to generalize
about operating parameters. Some strippers are designed to operate at
ambient bath temperatures, whereas others are recommended for
temperatures as high as 180°F. Stripping processes range from acidic to
basic. In general, the same equipment used for cyanide-based stripping can
be used for non-cyanide stripping. With acidic solutions, however, tank
liners might be needed to prevent corrosion.
Personnel trained in the use of cyanide-based strippers should also be able
to use non-cyanide strippers. For example, the U.S. Air Force reported that
higher skill levels were not required for the non-cyanide metal strippers
implemented at Kelly Air Force Base.
Non-cyanide strippers will have some impact on costs:Waste treatment costs will be reduced when switching to
non-cyanide strippers. If cyanide-based solutions are not
used elsewhere in the facility, the cyanide treatment system
can be eliminated.
A large capital outlay is not required when switching to a
non-cyanide stripper because the equipment requirements
are generally the same.
The costs of the makeup solutions will increase slightly.
Non-cyanide strippers have been available for many years. Major
drawbacks of this new technology include lack of speed, etching of some
substrates, and the need for electric current. As the disposal costs of
cyanide-based strippers continue to escalate, however, many companies
have switched to non-cyanide stripping methods. Production cycles have
been adjusted to account for the slower stripping speed.
A partial list of companies that supply non-cyanide strippers is found below.
This list does not constitute a recommendation.
Circuit Chemistry Corp.
Metalline Chemical Corp.
Frederick Gumm Chemical
Kiesow InternationalMacDermid Inc.
Patclin Chemical Company
Cyanide based strippers typically contain chelating agents and strong metal-
cyanide complexes that make waste treatment of spent strippers and
rinsewater extremely difficult. The use of non-cyanide based strippers
improves waste treatment, making it easier and more efficient.
At least one proprietary non-cyanide stripping process can crystallize
stripped nickel coatings. Crystallization extends the life of the stripping
solution indefinitely and creates a product that is readily recycled by
Non-cyanide metal strippers have the following benefits:
Significant potential for reducing waste treatment costs.
Often easier to recover metals from spent solutions.
Bath life is longer because higher metal concentrations can
One of the main incentives for eliminating the use of cyanide-based
stripping processes is to reduce health hazards to personnel. Although
cyanide in solution is itself very toxic, one of the main dangers for
electroplaters is the accidental addition of acid into the cyanide bath,
resulting in the formation of hydrogen cyanide gas, HCN. Dermal contact
with dissolved cyanide salts is less dangerous than inhaling HCN or
ingesting cyanide, but it nonetheless will still cause skin irritation and
Facilities that consider switching to non-cyanide strippers must consider the
health and safety aspects of the substitute, such as higher operating
temperatures, corrosivity, and so on.
Non-cyanide metal strippers have some disadvantages:
For some strippers, the recommended process temperatures
are high enough to cause safety problems. Operating at
lower temperatures can slow down the stripping reaction
and result in a loss of effectiveness.
Stripping rates for certain coatings might be lower than for
Some strippers can produce undesirable effects on substrate
metals, even if the stripper has been recommended by the
manufacturer for the application in question.
The removal of nickel coatings is a major use for non-cyanide strippers.
Advances in non-cyanide alternatives for nickel have been spawned by the
difficulty of treating nickel-cyanide waste streams. Opportunities for further
improvement still remain, however, as non-cyanide processes are
significantly slower than cyanide processes (8 hours versus 1 hour). Future
development will focus on speeding up the process and adjusting the
product to handle different metal coatings (e.g., silver) and substrates.
Janikowski, S.K., et al. 1989. Noncyanide Stripper Placement Program. Air
Force Engineering & Services Center. ESL-TR-89-07. May.
Alloys of zinc can be used to replace cadmium coatings in a variety of
applications. Cadmium is a heavy metal that is toxic to humans. In addition,
electroplated cadmium coating processes normally are performed in plating
solutions containing cyanide. Cyanide is highly toxic to humans and animal
life. The use of both cadmium and cyanide can be eliminated by
substituting an acid or non-cyanide alkaline zinc-alloy coating process for
a cyanide-based cadmium electroplating process.
How Does it Work?
Both zinc and zinc-alloy electroplating processes are very common and have
a long history in the electroplating industry. Recently, however, these
processes have been considered as possible replacements for cadmium
coatings (Zaki, 1993). Viable replacements for cadmium should provide
equivalent properties, such as corrosion protection and lubricity, at an
affordable cost. The ideal cadmium coating replacement is also a
non-cyanide-based process, because this also eliminate cyanide waste and
associated treatment costs.
Among the zinc and zinc-alloy processes evaluated as cadmium
replacements, the most promising are the following:
Zinc alone can provide corrosion protection equivalent to cadmium at
plating thicknesses above 1 mil. For thinner deposits, however, cadmium
will outperform zinc. Additionally, zinc coatings cannot match the other
properties for which cadmium is valued, e.g., lubricity. For this reason, zinc
is not considered to have wide potential for replacing cadmium (Brooman,
1993). Similarly, alloys such as zinc-iron may not qualify because they
cannot match cadmium’s appearance attributes. Tin-zinc is a potential
substitute for cadmium (Blunden and Killmeyer, 1993) but will probably
remain prohibitively expensive for most applications.
Table 3 compares relevant properties for several zinc alloys. The
identification of zinc-nickel and zinc-cobalt as the alloys with the greatest
potential for as a cadmium substitute is based on their properties and on the
range of applications for which these alloys have already seen commercial
use (see below).
Why Choose this
The ability of any alternative coating to replace cadmium depends on the
properties required by the application in question. Some zinc alloys have
as good and in some cases better resistance to corrosion, as measured in salt
spray tests. Few match cadmium for natural lubricity in applications such
as fasteners, however. In addition, where cadmium is selected for its low
coefficient of friction or for its low electrical contact resistance, none of the
candidates mentioned above may be suitable. Table 3 indicates that
applications requiring heat treatment would eliminate zinc-cobalt alloys as
Some of the operating features of the zinc-nickel and zinc-cobalt alloys are
listed in Table 4. Both zinc-nickel and zinc-cobalt can be plated from acid
or alkaline baths.
Acid zinc-nickel delivers a higher nickel content than the alkaline bath (10
percent to 14 percent versus 6 percent to 9 percent). Corrosion protection
increases with nickel content up to about 15 percent, thus favoring the acid
bath. Acid solutions, however, tend to produce deposits with poorer
thickness distribution and greater alloy variation between high and low
current density areas. Alkaline baths produce a deposit featuring columnar
structures (which tend not to favor applications that require bendability), as
opposed to the laminar structure deposited by the acid system. Alkaline
baths are simpler to operate and are similar to conventional noncyanide zinc
processes (Budman and Sizelove, 1993).
Zinc-cobalt deposits contain approximately 1 percent cobalt with the
remainder made up of zinc. The acid bath has a high cathode efficiency and
high plating speed, with reduced hydrogen embrittlement compared to
alkaline systems. Thickness distribution of the acid bath varies substantially
with the current density.
Existing electroplating equipment can be used for any of these alternativeprocesses. Therefore, a large capital expenditures would not be required to
switch to an alternative process. Conversion to an acid bath, however, does
require existing tanks to be relined. With older equipment, new tanks might
possibly have to be installed to provide the necessary corrosion resistance.
The costs associated with cyanide waste treatment can be eliminated for any
process line in which a cyanide-based cadmium process is replaced.
Acid baths have been used for some time in zinc and zinc alloy plating. The
desire to eliminate cyanide from the plating process has resulted in the
development of non-cyanide alkaline baths and chloride-based baths for zinc
coatings. The use of zinc-nickel alloys has gained ground because of their
potential to replace cadmium, particularly in Japan and other countries
where the use of cadmium coatings has been curtailed or prohibited for
several years. Zinc-nickel alloys have been introduced in Japan and
Germany in the automotive industry for fuel lines and rails, fasteners, air
conditioning components, cooling system pumps, coils and couplings
(Budman and Sizelove, 1993). Improved warranty provisions from vehicle
manufacturers such as Honda, Toyota and Mazda further boosted
applications for zinc alloys. Chrysler followed with new specifications for
zinc-nickel and zinc-cobalt in 1989, and Ford developed specs for alkaline
zinc-nickel to replace cadmium in 1990 (Zaki, 1993). Additional
applications include electrical power transmitting equipment, lock
components, and the maritime, marine, and aerospace industries. Zinc-
nickel coatings have also reportedly been substituted for cadmium on
fasteners for electrical transmission structures and on television coaxial
cable connecters (Brooman, 1993).
Zinc alloy plating systems are commercially available from numerous
Suppliers can be identified through articles or
in trade journals
as Metal Finishing, Plating
and Surface Finishing,
Replacing cyanide-based cadmium coating with one of the processes
described eliminates workplace exposure to both cadmium and cyanide, and
reduces environmental releases of both these chemicals.
Additional operational benefits may result depending on the properties of
the alloy relative to the cadmium deposit being replaced:
Corrosion resistance for zinc is as good as cadmium for
Zinc-nickel alloys have better wear resistance than
Zinc-cobalt deposits show good resistance to atmospheres
As discussed, the desired properties for the application must be matched to
the properties of the alloy.
Zinc and zinc-nickel alloy electroplating processes have the following
Electrical contact resistance is higher for zinc than for
Zinc and zinc-nickel alloy coatings do not have the
lubricity of cadmium coatings.
Acid zinc coatings have comparatively poorer throwing
power than cadmium, and deposits are not fully bright.
In general, plating with non cyanide-based plating
processes requires that parts be cleaner than for cyanide
The processes outlined above are well-developed and are available from
numerous vendors. These alternatives, however, have only recently been
considered as replacements for cadmium coatings. Industry recognizes that
the move away from cadmium plating is well underway and zinc alloys are
expected to play an important role as substitute (Zaki, 1993). Nonetheless,
more work needs to be done to compare these alternative coatings to
cadmium for specific applications.
Blunden, S.J. and A.J. Killmeyer. 1993. Tin-zinc alloy plating: a non-
cyanide alkaline deposition process. 1993
Brooman, E. 1993. Alternatives to cadmium coatings for
Plating and Surface Finishing.
Budman, E. and R. Sizelove. 1993. Zinc alloy plating.
Courter, E. 1990. Zinc-nickel alloy electroplating of components: corrosion
resistance is selling point for autos.
American Metal Market.
May 17. p. 17.
Dini, J.W. 1977. Electrodeposition of zinc-nickel alloy coatings.
on Alternatives for Cadmium Electroplating in Metal Finishing.
Gaithersburg, MD (October 4). Washington: U.S. Dept. of Energy. 38 pp.
Hsu, G.F. 1984. Zinc-nickel alloy plating: an alternative to cadmium.
Plating and Surface Finishing.
April. pp. 52-55.
Sharples, T.E. 1988. Zinc/zinc alloy plating.
Sizelove, R.R. 1991. Developments in alkaline zinc-nickel alloy plating.
Plating and Surface Finishing.
March. pp. 26-30.
Wilcox, G.D. and D.R. Gabe. 1993. Electrodeposited zinc alloy coatings.
Corrosion Science. 35(5-8).
Zaki, N. 1993. Zinc alloy plating.
1993 Products Finishing Directory.
The Blackhole Technology Process is an alternative to the electroless copper
method used in printed wire board manufacturing. The following qualities
make it environmentally attractive:
Fewer process steps
Reduced health and safety concerns
Reduced waste treatment requirements
Less water required
Reduced air pollution
How Does it Work?
Why Choose this
The chemistry in the Blackhole process avoids the use of metals (copper,
palladium, tin) and formaldehyde used in electroless copper processes. The
smaller number of process steps reduces the use of rinse water, decreasing
waste treatment requirements.
The Blackhole Technology Process uses an aqueous carbon black dispersion
(suspension) at room temperature for preparing through-holes in printed
wire boards (PWBs) for subsequent copper electroplating. The carbon film
that is obtained provides the conductivity needed for electroplating copper
in the through-holes. The process steps are described in the following
paragraphs and compared with the process steps used for the electroless
The Blackhole Technology Process eliminates the need for electroless
copper metalization of through-holes prior to electrolytic plating in the PWB
industry. Formaldehyde, a suspected carcinogen and water pollutant, is an
ingredient of the electroless copper plating process. The Blackhole process
eliminates this waste stream and avoids costs and environmental/health risks
associated with disposal or treatment of spent electroless copper plating
PWBs must be pretreated for desmear/etchback in both the Blackhole
Technology and electroless copper processes. Permanganate is the preferred
desmear process for Blackhole Technology because of its wide operating
conditions and the resulting hole-wall topography.
PWB manufacturers typically use the electroless copper process to plate
through-holes. The electroless copper process consists of the following
1. Acid cleaner
3. Micro etch (sodium persulfate
5. Activator pre-dip
11. Electroless copper bath
13. Sulfuric acid (10 percent) dip
15. Anti-tarnish dip
17. Deionized water rinse
18. Forced air dry
These steps are performed in order on a process line that uses an automated
hoist to move racks of parts from tank to tank. All of the rinses are single
use and generate large quantities of wastewater that contains copper. The
rinses following the electroless copper bath (from Step 11 on) contain
complexed copper, which is hard to treat using typical wastewater treatment
technology, such as metal hydroxide precipitation.
The Blackhole Technology process replaces the electroless copper process
for through-hole plating with a carbon black dispersion in water. The
Blackhole Technology process consists of the following process steps:
1. Blackhole alkaline cleaner
3. Blackhole alkaline conditioner
5. Blackhole bath
9. Anti-tarnish dip
l l . D r y
Steps 1 through 6 are performed, then repeated. Steps 7 through 11
complete the process. All process steps are performed automatically on
either a horizontal conveyor system or using existing hoists and bath
systems (see Figure 1).
Blackhole Technology Plating Line
Hollmuller Combistem CS-65
Source: MacDermid Inc.
The Blackhole Technology Process first uses a slightly alkaline cleaning
solution containing a weak complexing agent. The solution is operated at
135°F (57°C) to remove drilling debris from the hole-wall, to clean the
copper surfaces, and to prepare the hole-wall surface for the subsequent
A second alkaline solution containing a weak complexing agent serves as
the conditioner. This solution is applied at room temperature. The condi-
tioner neutralizes the negative charge on the dielectric surfaces, which helps
to increase the absorption of the carbon in the next step.
The Blackhole Technology step uses a slightly alkaline, aqueous carbon
black-based suspension operating at room temperature. The viscosity of the
solution is very close to water. The carbon particles have a diameter of 150
to 250 nanometers (1500 Angstroms to 2500 Angstroms).
Conventional plating tanks and horizontal conveyorized systems can be
used for the Blackhole Technology Process.
Material and Energy Requirements.
Compared to electroless copper, the Blackhole Technology Process uses
fewer individual process steps. Some process steps are repeated, which
reduces the floor space needed for the process baths. The number of
chemicals used also is reduced. The energy requirements should be about
the same, because both processes use a drier and several heated solutions.
Required Skill Level
The skill level required of system operators running the Blackhole process
is the same as or less than that for electroless copper processing.
If existing process equipment is used, the only installation cost is the
disposal of the electroless copper solutions, cleaning of the tanks, and
replacement with the Blackhole Technology process solutions.
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