When you see an automobile in the rain, its paint looks like it’s sweating because water and other small particles get trapped beneath the paint’s surface. That’s why companies use protective metal coatings on so many surfaces—from cars to semiconductors.
These coatings must be thin and strong to protect their substrates from damage, and they need to keep moisture or other potentially damaging substances out while still letting in light and air.
Vapor deposition is a passivation process that uses deposition techniques to achieve this. There are multiple ways to achieve this result, but we can classify them as either chemical deposition or physical deposition methods.
Both are useful for protecting substrates, but each has its own advantages.
What is Vapor Deposition?
A protective metal coating is a thin layer of metal that protects its substrate from corrosion or damage, applied through a passivation process using either physical or chemical vapor deposition. Technicians place the substrate inside a vacuum chamber, depositing a thin metal layer onto its surface through chemical or physical processes. Once applied, heating the coating and substrate allows the vapor to flow more freely and the coating to adhere more thoroughly.
Physical Vapor Deposition
Copper
This process vaporizes and condenses copper into liquid when it hits the substrate. The substrate is first coated in a thin layer of a material called a seed, then exposed to a stream of copper vapor.
The copper vapor particles adhere to the seed material, which serves as a base upon which they can grow, and when the growing particles slow down when hitting the seed, and grow into a thin layer of copper on the seed surface. As they remove the seed material from the surface, it reveals a thin layer of copper underneath.
Nickel
In this process, a nickel seed is first deposited on the substrate. Next, a carbon source forms a layer of hydrocarbon molecules on the nickel seed material, which is exposed to a stream of nickel vapor that cools down as it approaches the surface.
The nickel vapor condenses into a liquid as soon as it hits the hydrocarbon molecules, which serve as a base for the growth of a thin layer of nickel. Techs heat the substrate when the nickel layer approaches the seed layer and, by slowly removing the seed material from the surface, reveals the thin layer of nickel underneath.
Gold
This process vaporizes and condenses gold into liquid when it hits the substrate. The substrate is first coated in a thin layer of gold and deposited on the substrate. Meanwhile, heating the substrate to a temperature reduces the surface tension of the gold, causing it to flow freely.
The gold flows over the substrate and continues to build until it reaches its surface tension once again, at which point it stops growing. Slowly removing the gold from the surface reveals the thin layer of gold underneath.
Since gold is a precious metal, it’s not commonly used.
Chemical Vapor Deposition
Copper
In this process, a copper seed is first deposited on the substrate. This process requires sending a mixture of gases through the vacuum chamber, heating them to where copper atoms break off from the molecules, and depositing them onto the substrate where the copper seed is located.
Heating the substrate allows the vapor to flow freely and the copper atoms to adhere more thoroughly. After cooling the substrate, slowly removing the copper seed from the surface reveals the thin copper layer underneath.
Nickel
In this process, a nickel seed is first deposited on the substrate. This process requires sending a carbon source through the vacuum chamber, heating them to break it down into hydrocarbon molecules, and depositing them onto the substrate and the nickel seed.
Heating the substrate allows the vapor to flow freely and the hydrocarbon molecules to adhere more thoroughly. After cooling the substrate, slowly removing the nickel seed from the surface reveals the thin nickel layer underneath.
Platinum and Iridium
In this process, an iridium or platinum seed is first deposited on the substrate. This process requires sending a mixture of gases through the vacuum chamber, heating them to break platinum or iridium atoms, and depositing them onto the substrate and the platinum or iridium seed.
Heating the substrate allows the vapor to flow freely and the iridium or platinum atoms to adhere more thoroughly. After cooling the substrate, slowly removing the nickel seed from the surface reveals the thin iridium or platinum layer underneath.
In Sum
The benefits of coatings on metal surfaces have been around for a long time, and using vapor deposition to achieve surface coating is a modern technology.
Depending on the coating chosen and the type of metal surface, vapor deposition makes metal surfaces more resistant to scratching, making them easier to clean and maintain and perform better under abrasive conditions. It also protects metals against dyes and other chemicals, thus increasing their corrosion resistance.
The most popular types of metal surfaces that use vapor deposition include:
- Copper: Copper is popular because of its high conductivity and ability to conduct electricity. It’s also very malleable and doesn’t rust easily.
- Nickel: Similar to copper, it has high conductivity and malleability and doesn’t rust easily.
- Gold: Gold is a precious metal with great corrosion and tarnish resistance and is highly malleable.