When you think
of thin film coatings, you aren't likely to envision industrial
equipment such as drills bits, fasteners, stampings and other parts
and pieces that would go into heavy-duty applications. When you
think of these types of parts, you are more apt to think of heavy-duty,
thick coatings, something tough and strong. Not so at IonBond Inc.
(Madison Heights, MI). It provides customers all of these benefits
in a thin film. Strong, wear-resistant coatings are applied using
state-of-the-art cathodic arc physical vapor deposition (PVD), enhanced
arc PVD, unbalanced magnetron sputtering, chemical vapor deposition
(CVD) and plasma assisted chemical vapor deposition.
"We have seven coating centers throughout the United States,"
explained David Johns. "Each center has practical and technical
expertise in thin-film coating, surface conditioning and industrial
applications. The technical and engineering staffs at each facility
support the Corporate Technology Group in Madison Heights, which
develops new coatings and applications and provides failure analysis
and analytical services."
This can be seen in the QSFV (quality, speed, flexibility, value)
program within IonBond. The company has invested in its own fleet
of trucks to help with pickup/delivery and JIT requirements of its
customers. Also, IonBond has invested in a customized system for
monitoring the business. "We worked with a firm to customize
the software to fit our needs," commented Rajiv Ahuja, president
and CEO.
This specialized management tool is called "MAJIC." MAJIC
is designed to track a customer product and record processing history,
while monitoring a whole range of operational parameters, like product
turnaround times and capacity utilization. Structured around the
ISO 9000 quality system, MAJIC tracks a tool from the time it enters
a facility to the moment it is delivered. "Managing several
service centers from a central location can be difficult. We needed
a way to maintain the data in a centralized location so that everyone
could access it anytime. Any of our employees in the country can
call in and check the status of a job," said Mr. Ahuja.
Although it has been challenging to meet the needs of customers,
IonBond has found that educating customers is its greatest challenge.
"Our most significant challenge has been customer education
and awareness," stated Mr. Ahuja. "These coatings (CVD,
PVD) have been around for 30 years; however, they are only now seeing
significant activity in the market. People do not realize what these
coatings can do for their tools, plumbing fixtures, drill bits and
more." Even though the coating costs more initially, it is
more cost-effective because it lasts longer.
Determining which deposition process to use depends on the end use
of the product. PVD is used for close tolerance tooling, such as
milling tools, round shank tools, trim tooling, plastic molds, punches
and brazed carbide tooling. PVD uses low temperature, line-of-sight
operation. Parts rotate within the chamber, and it can be used on
most metals and requires no post-heating.
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High
Rate Thin-Film Production
The Missile Defense Agency (Alexandria, VA) recently reported
on a pulsed laser deposition process that produces high-quality
thin films at high rates. With funding from the Ballistic
Missile Defense Organization SBIR funding, AMBP Tech Corporation
has developed laser-assisted molecular beam deposition (LAMBD).
This method can be used to create uniform, high-purity films
from 50 angstroms to 10 microns with very flat morphologies.
LAMBD simplifies the production of complex films such as carbide,
nitrides and metal alloys. Similar to pulsed laser deposition,
the LAMBD source uses a laser to rapidly heat a target, generating
a cloud of evaporated target material. This cloud simultaneously
combines with a pulse reactant gas, often oxygen or hydrogen.
The ablated target material and gas form a chemical reactor
from which nanoparticles can be generated or from which films
can be deposited.
Product molecules are expelled from the pressurized LAMBD
source into a vacuum chamber and deposited on the substrate.
With each pulse, a known amount of material is deposited.
By adjusting the laser power, the amount of material deposited
by each pulse can be varied. Regulating the total number of
pulses used in the deposition process allows for precise control
of film thickness. Deposition rates are hundreds of angstroms
per minute.
A prototype system with 3-inch wafer capability has been developed.
Work has started to find ways to spread material over larger
areas. For more information, contact Dr. James Garvey, AMBP
Tech Corporation, 716-639-0632; www.ambptech.com.
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CVD is used
on loose tolerance tooling. The process involves high temperatures
and a gaseous environment. With CVD, everything is coated, and masking
is almost impossible. Often heat treating is required after CVD,
and there are material restrictions.
"Vacuum coatings offer more flexibility. I see large potential
for growth, particularly in the decorative business," stated
Mr. Ahuja. "But it depends on how fast we educate designers
and engineers and push down prices. We also have to continue to
develop new coatings, such as diamond-like coatings that are good
for cutting tools and other components. We have to remind engineers
to design products with the coating in mind. That way, they will
have a more effective product than if they simply adapted a coating
to product."
Bernex® PaCVD is a new process for depositing amorphous coatings
consisting of diamond-like carbon (ADLC). The coatings are deposited
by a plasma activated CVD process. The patented process enables
the deposition of smooth, adherent coatings at temperatures below
200C. This opens a new field in the coating of steels in hardened
and tempered conditions and aluminum and titanium alloys, since
the mechanical properties of the base material are not affected.
Here is a brief tutorial on the different deposition processes a
summarized from IonBond's website, www.ionbond.com.
Physical Vapor Deposition.
PVC
includes a number of vacuum-coating processes during which material
is physically removed from a source by evaporation or sputtering
and then transported through a vacuum using the energy of the vapor
particles and finally condensed as a film on the substrate. All
PVD processes can be separated into three stages: 1) Emission from
a vapor source; 2) Vapor transport in a vacuum; and 3) Condensation
on the substrate.
The IonBond PVD process uses a vacuum arc to evaporate material
from a cathode to produce a stream of highly active and excited
coating material. The coating units consist of a vacuum chamber
and a number of arc evaporation sources that are arranged in the
chamber walls. Each source is about 63 mm in diameter, although
some are larger.
A number of metals, alloys and electrically conductive, semi-conductive
and insulating compounds can be deposited. PVD is used almost exclusively
to deposit films 0.03-5mm thick. The use of PVD hard coatings, particularly
titanium nitride (TiN), on cutting tools and other wear components
has grown because it has a hardness of greater than Rc 80, increasing
the wear rate. The TiN coating also provides chemical resistance,
because it is a stable coating. It prevents chip welding in cutting
tools because of the anti-galling properties of the coating. TiN
also has a lower coefficient of friction than hard chromium.
The most commonly used PVD processes are ion-assisted processes:
vacuum arc evaporation, electron beam evaporation and high-rate
magnetron sputtering. These can be deposited using reactive and
non-reactive methods.
Reactive PVD. During reactive PVD, carbides, carbonitrides,
nitrides, oxides and other compound types are deposited by introducing
a reactive gas such as nitrogen or oxygen into the physical vapor
stream. Reactions between the gas and vapor occur at the substrate
surface, in transit or at the source surface, as well as on the
chamber walls and other surfaces. The primary reaction site is the
substrate.
Plasma Enhancement. Plasma enhancement increases the
number of ions, electrons, fragmented molecules and excited neutrons
in the gas or vapor. To use plasma enhancement, inert and/or reactive
gases must be present at pressures that can maintain a gas discharge.
When used with a negative substrate bias, the increased ion bombardment
generally results in improved film properties, since the atoms,
molecules and molecular fragments react more readily with the growing
film.
The electrode attached to the auxiliary discharge supply is the
plasma enhancement device. High frequency voltage applied to this
electrode is another way to create a gas discharge. Another way
to generate plasma enhancement is to accelerate electrons from a
thermionic filament through the transport region to the auxiliary
anode.
The voltage needed is about 100-1000v at pressures of 10 to 30e
-5 torr. Once started, the gas discharge clamps the voltage at a
level determined by the electrode geometry, surface composition
and gas pressure and composition.
Enhanced Arc. This system is a patented deposition
system that uses high strength magnetic fields in direct line-of-sight
configuration to suppress macro-particle emission. This results
in the enhancement of plasma ionization, energy and density and
the near elimination of macroparticles in the deposited film. High
ionization assists in the substrate conditioning and promotes adhesion,
particularly when depositing amorphous diamond.
Ion Bombardment. Ion bombardment produces films with
extremely high adherence and good physical properties. In most ion-assisted
PVD processes, ions gain energy because of a negative bias voltage
applied to the substrates. For nonconductive substrates or coatings,
a high frequency bias voltage is applied and positive ions are accelerated
toward the substrates during the negative phase. Electrons neutralize
substrate charging during the positive phase of each cycle. In most
PVD processes, ion bombardment is supplied by argon or reactive
gas ions from a gas discharge.
Vacuum Arc Deposition. During vacuum arc evaporation,
metal evaporates from a cathode source as a result of intense localized
heating by arc spots that move randomly across the cathode surface.
The vapor source remains solid while the major portion of the metal
vapor is ionized.
Because this type of PVD is highly localized, cathodes can be used
in any position, allowing for greater flexibility in designing systems
with multiple sources for coating large parts or large quantities
of parts. Also, the metal vapor is used for heating the substrate
and surface preparation as well as coating. Substrates are heated
using metal-ion bombardment and operating one or more arc sources
while applying a voltage to the substrates. This heats the parts
and conditions their surfaces to increase film adhesion.
Reactive deposition occurs while operating arc sources in the presence
of a reactive gas using substrate bias voltages -75 to -400v. This
produces dense stoichiometric films with high adhesion.
Electron Beam Reactive Deposition. The current electron
beam industrial processes are thermionically enhanced triode-ion
plating, hollow cathode discharge and coaxial. In each process,
an electron beam heats metal, evaporating it from a molten pool.
The substrates collect the vapor from bottom-mounted sources. Substrates
are usually rotated to increase film thickness. The reactive gas
pressure is closely controlled to achieve good film stoichiometry.
Thermionically
enhanced. Once the chamber is pumped down, substrates are
heated to at least 570F using argon ion bombardment. An argon
ion discharge is used to sputter clean the substrate surface.
The thermionic electrons accelerated from the hot filament enhance
the strength of this discharge. During coating, a bias of several
hundred volts is applied to the substrate, and the reactive gases
are introduced into the chamber. The electron beam is a high-voltage,
low-current unit the produces little ionization.
Hollow cathode discharge. This process is similar to thermionically
enhanced triode ion plating. The hollow cathode discharge gun
produced a high-current electron beam that strikes the metal source
at about 100 eV. About 10-20% of the metal vapor is ionized as
it passes through the electron flux.
Coaxial
electron beam. This reactive deposition process differs from
the others. The electron source contains magnetically enhanced,
thermionically supported discharge that emits a high electron
current along with ionized gas. The substrates are heated using
electron bombardment. The positive side of the discharge supply
is connected to the substrate. When the substrate temperature
reaches 570F, electrons from the source are accelerated to the
auxiliary anode and then sputter cleaned with argon ions. During
cleaning the substrates are biased negatively.
High
Rate Reactive Magnetron Sputtering. During this process,
metal vapor is sputtered from cathode sources by an intense inert
gas discharge that is confined to a region within four inches of
the cathode source. The vaporization rate per unit area is relatively
low, but large single sources and multiple sources can be used.
The arrangement of the components and gas inlets maximize the amount
of molecules that will react on the substrate before reaching the
cathode. It is necessary to balance the flow rate of reactive gas
with the metal vaporization rate to achieve film stoichiometry while
maintaining a clean cathode surface. Argon ion bombardment is often
used to sputter clean the substrate and provide additional heat.
Chemical Vapor Deposition.
This is a different process from vacuum evaporation, ion plating
or sputtering. It is a heat-activated process that relies on the
reaction of gaseous chemical compounds with heated substrates. The
main reactive vapor can be chloride, bromide, iodide or fluoride,
or a metal. Generally, deposition of a pure metal from the halide
occurs either by hydrogen reduction at a specific temperature or
by direct pyrolytic decomposition at a higher temperature.
Whenever carbide, nitride or borides are desired, the metal halide
vapor is accompanied by an additional reactive species such as methane,
nitrogen or boron trichloride. The addition of reactive species
lowers the free energy of the reaction products so that the compound
is formed in preference to the pure metal. Manipulation of the reactor
pressure, temperature and/or reactant composition can also influence
the deposition products.
Advantages. CVD is a versatile process that can be
used on a wide configuration of substrates. It produces high density,
high purity and high strength coatings. The strength is dependent
on crystal structure and size, purity, density and internal stress.
CVD deposits are usually more ductile because of their purity and
have comparable or higher mechanical strength than wrought material.
However, not all materials exhibit high strength. Pure tantalum
and pure columbium have low yield strengths and high ductility in
the vapor deposited condition.
Coatings Deposited. A number of pure metals, carbides, nitrides,
borides, silicides and oxides of metals can be deposited using CVD.
Coating thickness ranges from 0.0002-0.050 inch. Co-deposition of
TiC and TiN to form titanium carbonitride using the Bernex Moderate
Temperature CVD process is expanding in use. Chromium deposition
on steel substrates, resulting in carbides of chromium and iron,
(CrFe)7C3, provides excellent resistance to corrosion and cold welding.
Applications. The greatest application for CVD is
the hard coating of tools fabricated from high-speed steels, stainless
steels and cemented carbides. Both TiC and TiN enhance the life
of carbide cutting tools and high-speed punches and dies. The process
is also used to coat tungsten, platinum and rhenium used in electronic
hardware, as well as integrated circuits for microelectronic application
and solar cell fabrication.
The Process. Important aspects of the process include
gas pressure; temperature and velocity; reactant composition; material
composition; substrate cleanliness and temperature; storage flow
and recovery systems; scrubber systems for the by-products; and
the composition and construction of the vessel.
Substrates must be free of grease and oil. IonBond uses aqueous
cleaners, sodium hydroxide and ultrasonic cleaning. The substrates
must tolerate intense heat, since temperatures in the chamber vary
from 400-3600F. Small pieces are much easier to heat up than large
pieces. Small pieces may have to be racked or rotated. Because the
surface temperature is critical, and cracks, crevices and recesses
frequently maintain a higher temperature, deposits will be easily
formed in these areas. However, the reactant gases are limited in
their ability to penetrate crevices. This tends to offset the effect
of temperature on the deposition rate.
Gas systems. CVD systems require a gas feed system
so that the active material can be injected into the deposition
chamber and exhaust products removed.
Reaction temperature. Temperature must be maintained
during the process to prevent excess coating buildup on tanks as
well as on parts. When decomposing the metal compound, the substrate
is held at a substantially higher temperature than any other part
of the system. Because of this, the reaction chamber may be more
of a high temperature problem than any other part of the system.
Most reactions occur in an anhydrous and anaerobic environment,
often at sub-atmospheric pressures.
Temperatures during deposition range from 1500-2200F. Temperature
and pressure depend on what properties are wanted in the deposit.
The deposition rate can vary from 0.07 mm/min at low temperatures
to 25 mm/min at higher temperatures. Thick uniform coatings with
refined grain structure are also the result of deposition temperature.
Low temperature processing is usually desirable, although a tradeoff
with deposition rate is often made. Fewer CVD reactions occur at
temperatures below 1500F; however, exposing the substrate to electrical
plasma in the gas phase during coating can lower the temperature
(plasma enhanced).
Reaction pressure. Deposition at sub-atmospheric pressure
improves the uniformity, grain size and composition of most CVD
films. Special pumping systems are required because the gases are
hot and often corrosive. One way around this is to trap the gases
and cool them before they reach the vacuum pumps. If pressures greater
than 50 torr are used, water jet exhausters or watering pumps can
be used. Inexpensive polyvinyl chloride exhausters can be used if
gases are cooled before entering the equipment. Toxic by-products
should be neutralized or eliminated.
"The coating processes take a lot of time," explained
Babu Mamidipally, engineer. "From a customer service standpoint
it is often difficult to explain the time involved, since the customer
wants the part as soon as possible. But these parts are not just
sitting around the shop. Most customers have learned, however, that
the process is better for their tools and equipment. It is just
that they don't turn it over to us until they are 'at the end of
their rope.'"
IonBond is a pioneer in the thin film coatings industry. More than
20 years ago the company made high performing low-cost TiN coating
a reality. It designed and built the first commercial cathodic arc
PVD systems. The patented enhanced arc source is another IonBond
technical advancement. The enhanced arc reduces the macro particles
in cathodic arc coatings, providing a smoother, defect-free thin
film and allows deposition of innovative materials like TETRABOND®
tetrahedral amorphous carbon.Over the years, the company's technical
developments have expanded the scope of PVD and CVD coating applications.
It invented the recoating concept that is used to extend the life
of perishable tooling and pioneered the use of PVD coatings on medical
devices. When it became apparent that the company's TiN did not
meet all customer needs, it developed Cathodic Arc TiAIN, AITiN,
TiCN, CrN and ZrN coatings. And it continues to meet its customers'
needs by developing new coatings and application technologies.
