SURFACE COATING BY PHYSICAL VAPOR DEPOSITION

Revision Date: 4/03
Process Code: Navy/Marines: IND-004-03; Air Force: MT03; Army: ELE, MTF
Usage List: Navy: High; Marines: Medium; Army: Low; Air Force: High 
Alternative For: Certain electroplating processes like cadmium plating
Compliance Impact: Not applicable
Applicable EPCRA Targeted Constituents and CAS Numbers: N/A


Overview: Physical Vapor Deposition (PVD) comprises a group of surface coating technologies used for decorative coating, tool coating, and other equipment coating applications. It is fundamentally a vaporization coating process in which the basic mechanism is an atom by atom transfer of material from the solid phase to the vapor phase and back to the solid phase, gradually building a film on the surface to be coated. In the case of reactive deposition, the depositing material reacts with a gaseous environment of co-deposited material to form a film of compound material, such as a nitride, oxide, carbide or carbonitride.

There are three basic process categories considered as PVD technologies: ion plating, evaporation, and sputtering. All utilize the same three fundamental steps to develop a coating. Each of the PVD technologies generate and deposit material in a somewhat different manner, requiring equipment unique to each process. The three fundamental steps include:

1. Vapor phase generation from coating material stock by -
  • Evaporation 
  • Sputtering 
  • Arc Vaporization
  • Chemical vapors and gases

2. The transfer of the vapor phase from source to substrate by -

  • Line-of-sight 
  • Molecular flow 
  • Vapor ionization by creating a plasma 

3. Deposition and film growth on the substrate

These steps can be independent or superimposed on each other depending on the desired coating characteristics. The final result of the coating/substrate composite is a function of each materials individual properties, the interaction of the materials and any process constraints that may exist.

The selection criteria for determining the best method of PVD is dependent on several factors;

  • The type of material to be deposited 
  • Rate of deposition 
  • Limitations imposed by the substrate, such as, the maximum deposition temperature, size and shape 
  • Adhesion of the deposition to the substrate 
  • Throwing power (rate and thickness distribution of the deposition process, i.e., the higher the throwing power, the better the process ability to coat irregularly-shaped objects with uniform thickness)
  • Purity of coating materials 
  • Equipment requirements and their availability 
  • Cost 
  • Ecological considerations 
  • Abundance of deposition material 

PVD is a desirable alternative to electroplating and possibly some painting applications. PVD can be applied using a wide variety of materials to coat an equally diverse number of substrates using any of the three basic PVD technologies to deposit a number of desired finishes of variable thickness with specific characteristics.

The application of PVD surface coating technologies at large scale, high volume operations will result in the reduction of hazardous waste generated when compared to electroplating and other metal finishing processes that use large quantities of toxic and hazardous materials.

 

Compliance Benefit:

PVD is a desirable alternative to electroplating and possibly some painting applications because it generates less hazardous waste and uses less hazardous materials (i.e., no plating baths).

The reduction of hazardous waste helps facilities meet the requirements of waste reduction under RCRA, 40 CFR 262, Appendix, and may also help facilities reduce their generator status and lessen the amount of regulations (i.e., recordkeeping, reporting, inspections, transportation, accumulation time, emergency prevention and preparedness, emergency response) they are required to comply with under RCRA, 40 CFR 262. In addition, since bath solutions are eliminated (i.e., less hazardous chemicals are used at the facility) there is less chance that the facility would exceed reporting thresholds for hazardous substances/chemicals under SARA Title III (40 CFR 300, 355, 370, and 372; and EO 12856). This technology also uses considerably less water than the traditional electroplating operations and as required under EO 12902, Energy Efficiency and Water Conservation at Federal Facilities. In addition, this type of system may require an air permit.

The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.

 

Materials Compatibility:

PVD coating processes are compatible with most metals and some plastics either as coatings or as substrates. However, temperature constraints may limit the degree to which dense coatings can be deposited on some plastics. Finally, PVD processes do not normally produce the kind of coatings that work well where lubrication is required. Thus, PVD coatings are not usually good choices for parts such as fasteners.


Safety and Health:

The safety and health issues must be evaluated on a case-by-case basis.

Consult your local Industrial Health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.


Benefits:
  • PVD coatings are sometimes harder and more corrosion resistant than coatings applied by the electroplating process. Most coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable that protective topcoats are almost never necessary. 
  • Ability to utilize virtually any type of inorganic and some organic coating materials on an equally diverse group of substrates and surfaces using a wide variety of finishes. 
  • More environmentally friendly than traditional coating processes such as electroplating and painting. 
  • More than one technique can be used to deposit a given film.

 

Disadvantages:
  • Specific technologies can impose constraints; for example, line-of-sight transfer makes coating annular shapes practically impossible.
  • Some PVD technologies typically operate at very high temperatures and vacuums, requiring special attention by operating personnel. 
  • Requires a cooling water system to dissipate large heat loads. 
  • Selection of the best PVD technology may require some experience and/or experimentation. 
  • High capital costs. 

 

Economic Analysis:

Economic considerations are probably the primary hindrance preventing conversion of plating operations to vapor deposition processes. A rough estimate of the capital cost for a new vapor deposition installation is several hundred thousand dollars. Operating costs are roughly equal to electroplating, although plating can be slightly less labor intensive.

 

NSN/MSDS: None identified.

 

Approving Authority:

Appropriate authority for making process changes should always be sought and obtained prior to procuring or implementing any of the technologies identified herein.

 

Points of Contact: For more information

Vendors:

This is not meant to be a complete list, as there may be other suppliers of this type of equipment.

PVD Product and Services Directory
Society of Vacuum Coaters
71 Pinot Place, NE
Albuquerque, NM  87122
Phone: (505) 856-7188

 

Sources: ASM Handbook, Vol. 5. Surface Engineering, ASM International, 1994.