1 2 3 4 5 6

Operating Features - Guide to Cleaner

Hajmi356.97 Kb.

Operating Features

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.

Section Three


A partial list of companies that supply non-cyanide strippers is found below.

This list does not constitute a recommendation.

Operational and

Product Benefits

Circuit Chemistry Corp.

Metalline Chemical Corp.

Electrochemical, Inc.

Metalx Inc.

Frederick Gumm Chemical


Kiesow International

MacDermid Inc.

OMI International

Patclin Chemical Company

Witco Corporation

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

commercial firms.

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

be tolerated.

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




Section Three

Hazards 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

cyanide-based counterparts.

Some strippers can produce undesirable effects on substrate

metals, even if the stripper has been recommended by the

manufacturer for the application in question.

Summary of

Unknowns/State of


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.


Pollution Prevention


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

Page 22

Section Three

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


Reported Applications

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

a substitute.

Operating Features

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.

Page 23

Section Three

Page 24

Section Three

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

Page 25

Section Three

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 alternative

processes. 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.

Reported Applications

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

Page 26

Section Three

advertisements appearing 

in trade journals 


as Metal Finishing, Plating

and Surface Finishing, 


Products Finishing.

Operational and

Product Benefits

Hazards and


Summary of

Unknowns/State of


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

many applications.

Zinc-nickel alloys have better wear resistance than


Zinc-cobalt deposits show good resistance to atmospheres

containing SO,.

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

based processes.

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.

Page 27


Blunden, S.J. and A.J. Killmeyer. 1993. Tin-zinc alloy plating: a non-

cyanide alkaline deposition process. 1993 


pp. 1077-1081.

Brooman, E. 1993. Alternatives to cadmium coatings for

electrical/electronic applications. 

Plating and Surface Finishing. 


pp. 29-35

Budman, E. and R. Sizelove. 1993. Zinc alloy plating. 

1993 Products

Finishing Directory. 

pp. 290-294.

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. 

Products Finishing. 

April. pp.


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). 

p. 125l-8.

Zaki, N. 1993. Zinc alloy plating. 

1993 Products Finishing Directory. 




Pollution Prevention


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

Page 28

Section Three

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

copper method.


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


Operating Features

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.

Process Comparison

PWB manufacturers typically use the electroless copper process to plate

through-holes. The electroless copper process consists of the following

operational steps:

Page 29

1. Acid cleaner

2. Rinse

3. Micro etch (sodium persulfate


4. Rinse

5. Activator pre-dip

6. Catalyst

7. Rinse

8. Rinse

9. Accelerator

10. Rinse

11. Electroless copper bath

12. Rinse

13. Sulfuric acid (10 percent) dip

14. Rinse

15. Anti-tarnish dip

16. Rinse

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

2. Rinse

3. Blackhole alkaline conditioner

4. Rinse

5. Blackhole bath

6. Dry

7. Micro-etch

8. Rinse

9. Anti-tarnish dip

10. Rinse

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).

Page 30

Section Three

Figure 1

Blackhole Technology Plating Line

Hollmuller Combistem CS-65

Source: MacDermid Inc.

Page 31

Section Three

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

conditioning step.

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.

Do'stlaringiz bilan baham:

©2018 Учебные документы
Рады что Вы стали частью нашего образовательного сообщества.