What is PVD Coating?

PVD stands for Physical Vapour Deposition and is a process done in a Vacuum Chamber that enables the deposition of exotic materials on all types of Metal, Plastic and Ceramic objects. The material to be deposited is Vapourised and then deposited on the target object either in the same elemental form or after it has reacted with some gas to form some other molecule that has some desirable properties. Titanium is a commonly used material in PVD coatings and is vapourised from a Titanium Target , then made to react with Nitrogen to form TiN (Titanium Nitride) which is then deposited on the object. Molecules like TiN have desireable properties like Hardness that protect the coated object from wear besides having a gold like colour that closely matches that of gold.

PVD machines comprise of two broad subsystems:

Vacuum Chamber and pumps: Better systems are designed to prevent the formation of leaks thereby reducing downtime. Secondly the Sizing of the Vacuum pumps must be done judiciously to reduce the time for Vacuum formation. This enables more cycles to be run each shift.

Electrical controls and power electronics for performing the actual coating in Vacuum. The actual Arcing/Sputterring, which are the two mechanisms of PVD coating is done by accurate control of current and voltages that keep the process stable and repeatable. In LKBT machines Solid State Thyristorised current control is used. Moreover all the sequence of operations is controlled by PLCs and optionally by Full Computer control.

A typical cycle for Coating an object could be something as follows:

• Load objects into the PVD Chamber.

• Create Vacuum.

• Clean the objects in Vacuum using high energy Argon Bombardment.

• Deposit TiN on the objects to the desired thickness level.

• Deposit a small layer Gold on the TiN surface to get a perfect colour match (Assuming the object has to be Gold Plated)

• Remove Vacuum and take out objects.
  
  The TiN layer below the gold layer protects the gold layer by allowing the softer gold particles to get lodged between the valleys and crests of the TiN layer. This mechanism will let the layer look like Gold for a longer period while actually using a very small quantity of gold.
  
  Importance of Cleaning of items to be coated:
  
  Of prime importance in the PVD process is the pre-cleaning of Objects to be coated. This aspect of PVD coating is sometimes overlooked and consequently results in rejections. Cleaning and other pre treatments are of vital importance to the successful running of any PVD coating process.
  
  Advantages of PVD over conventional coating processes:

1. PVD is a non polluting process.
    

2. It is done in Vacuum which is a clean environment and hence the process is very repeatable.
   

3. High performance films like TiN, ZrN , for abrasion and corrosion resistance, can be made in PVD which are not possible otherwise.
    

4. Coatings on various base materials like Plastic, Metals, and Ceramics can be done with minor modifications in the process.
    

5. Thinkness of coatings are typically under 1 micron and hence the surface of the object being coated is faithfully reproduced.
    

6. Multilayer coatings can be made for getting multiple advantages.
   
   Disadvantages of PVD Coatings:
   
   Thickness of the layer cannot be built up since it is extremely hard .This can be a disadvantage where thickness is desireable, as in the case of levelling provided by a thick layer of nickle plating.