Written By Matt Hughes – President – Semicore Equipment, Inc.
PVD stands for Physical Vapor Deposition. PVD Coating refers to a variety of thin film deposition techniques where a solid material is vaporized in a vacuum environment and deposited on substrates as a pure material or alloy composition coating.
As the process transfers the coating material as a single atom or on the molecular level, it can provide extremely pure and high performance coatings which for many applications can be preferable to other methods used. At the heart of every microchip, and semiconductor device, durable protective film, optical lens, solar panel and many medical devices, PVD Coatings provide crucial performance attributes for the final product. Whether the coating needs to be extremely thin, pure, durable or clean, PVD provides the solution.
It is used in a wide variety of industries like optical applications ranging from eye glasses to self-cleaning tinted windows, photovoltaic applications for solar energy, device applications like computer chips, displays and communications as well as functional or decorative finishes, from durable hard protective films to brilliant gold, platinum or chrome plating.
The two most common Physical Vapor Deposition Coating processes are Sputtering and Thermal Evaporation. Sputtering involves the bombardment of the coating material known as the target with a high energy electrical charge causing it to “sputter” off atoms or molecules that are deposited on a substrate like a silicon wafer or solar panel. Thermal Evaporation involves elevating a coating material to the boiling point in a high vacuum environment causing a vapor stream to rise in the vacuum chamber and then condense on the substrate.
What Makes PVD Coatings Highly Durable, Corrosion and Scratch Resistant?
Being able to apply coatings at the atomic level using PVD allows control of structure, density and stoichiometry of the films. Using certain materials and processes, we can develop specifically desired attributes of the physical vapor deposited film like hardness, lubricity, adhesion and more.
These coatings can reduce friction and provide a barrier against damage. The applications for these coatings are ever expanding. Aerospace, automotive, defense, manufacturing and more where long lasting durability is crucial.
This type of physical vapor deposition coatings can also be highly resistant to tarnishing and corrosion, enabling them to be used for a wide range of decorative finishes with colors that do not fade. A PVD gold or platinum coating produces brilliant finishes that make watches highly resistant to scratches and scrapes that cause less resilient processes to wear off.
Titanium nitride and similar coatings offer beautiful finishes that are also very resistant to corrosion and wear. This makes them widely used on household items such as door handles, plumbing fixtures and marine fixtures as well as machining tools, knives, drill bits, etc. It produces coatings with superior hardness, durability and resistance to wear.
Are PVD Coatings Safe?
Physical Vapor Deposition processes are an environmentally friendly or “plating” technique that greatly reduces the amount of toxic substances that must be used, manage and disposed of as compared to other “wet” processes that involve fluid precursors and chemical reactions used to achieve the same result. Because it is capable of producing extremely pure, clean and durable coatings, Physical Vapor Deposition is the technology of choice for the surgical and medical implant industry.
How are PVD Coatings Applied?
Whether the specific application process is Sputtering or Thermal Evaporation, both physical vapor deposition processes are fundamentally high vacuum techniques, vaporizing a source material to a plasma of atoms or molecules and depositing them on a wide range of substrates. Carried out in a high vacuum chamber with a pressure approximating outer space at 10-2 to 10-6 Torr (102 to 104 millibar), the process usually takes place between 50 and 500 Degrees C.
The object to be coated is secured in a fixture and placed in the vacuum deposition chamber. The chamber is pumped down to the optimum pressure depending upon the coating materials, substrate and process requirements used, and the object to be coated is often preheated and plasma cleaned.
What are Common PVD Coating Target Materials?
The coating material that is going to be sputtered or vaporized is known as a “target” or “source material”. There are hundreds of materials commonly used in PVD. Depending on what the end product is, materials range from metals, alloys, ceramics, compositions and just about anything from the periodic table.
Some processes require unique coatings like carbides, nitrides, silicides and borides for specialized applications. Each have special qualities tailored to specific performance requirements. Graphite and titanium for example are often used in high performance aerospace and automotive components where friction and temperature are crucial success factors.
To achieve a uniform thin film coating thicknesses that are often a few atoms or molecules thick, parts to be coated are often rotated on several axis at a uniform speed, or placed on conveyor belts moving past the deposition material’s plasma stream. Single or multi-layered coatings can be applied during the same deposition cycle.
Why is Argon Gas Used for PVD?
Argon is an inert gas which means it cannot chemically combine with other atoms or compounds. This assures that the coating material remains pure when it enters the vapor phase in the vacuum chamber before it is deposited on the substrate.
Additionally, reactive gasses such as nitrogen, oxygen or acetylene can be introduced into the vacuum deposition chamber to produce compounds that create a very strong bond between the coating and substrate when it’s deposited. Although the thin film depositions can be several angstroms to many microns thick, they form an extremely adherent coating that performs well in many applications like decorative finishes, electrical and other functional coatings. The applications are limitless!
Of all of the benefits of the PVD Coating process that produce some of the toughest, most brilliant and cutting edge technology of our time ranging from microchips to solar panels, none is more important than the fact that PVD Coatings can be applied with no toxic residues or byproducts which degrade our planet’s environment.
The two most common techniques of Thin Film Physical Vapor Deposition or PVD are Thermal Evaporation and Sputtering. Thermal Evaporation involves heating a solid material that will be used to coat a substrate inside a high vacuum chamber until it starts to boil and evaporates producing vapor pressure. Sputtering involves the bombardment of a target material with high energy particles that are to be deposited on a substrate like a silicon wafer or solar panel. Each thin film deposition process has advantages and disadvantages depending upon the specific application… Read More
Thermal Evaporation involves heating a solid material inside a high vacuum chamber to take it to a temperature which produces a vapor pressure. Inside the vacuum chamber, even a relatively low vapor pressure is enough to raise a vapor cloud. This evaporated material now constitutes a vapor stream, which traverses the chamber and hits the substrate, sticking to it as a coating or thin film…. Read More
Sputtering is a thin film coating technique where a target material to be used as the coating is given an electrical charge causing it to be bombarded with ionized gas molecules in a vacuum environment causing atoms to be “Sputtered” off into the plasma. These vaporized atoms are then deposited when they condense as a thin film on the substrate to be coated… Read More