Polymer Seals for Semiconductors
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Polymer Seal Options for Semiconductors

The manufacturing of semiconductors and semiconductor-related products requires reliable, high purity seals that can survive harsh operating conditions. The right sealing solution can reduce downtime, increase production efficiency, reduce power requirements, and increase process reliability

Seal Environments in Semiconductor Applications

The operating environments for seals in semiconductor applications are challenging to say the least. They may be exposed to fluorine and oxygen plasmas, as well as chlorinated gases, at extreme temperatures or vacuum conditions. Semiconductor seals are typically exposed to highly aggressive, corrosive fluids, such as acids, bases, amine-based strippers, and solvents. Such operating environments can quickly lead to seals that fail prematurely or experience rapid degradation. In addition, because of the delicate nature of semiconductors with respect to contamination, most applications require ultra-high levels of purity.

Semiconductor Applications for Seals

  • Semiconductor processing systems
  • Rotary shaft seals for gearboxes and processing pumps
  • High speed seals

Key Material Properties for Semiconductor Seals

When it comes to semiconductor seals, there are certain material properties that are often key:

  • Reliable mechanical performance
  • Extremely low levels of both anionic and cationic impurities
  • Low levels of TOC (Total Organic Carbon) 
  • Good performance in ultra pure deionized water
  • Low permeation rates
  • Reduced IR (Infrared Absorption)
  • Resistance to both dry and wet process chemistry
  • Minimal outgassing (which can be a major problem at continuous high temperatures)
  • Minimal particle generation 
  • Ultra-high purity
  • Low friction 

Types of Semiconductor Seals

While some applications may simply need a more traditional lip seal, other options include labyrinth seals, spring-energized seals, and encapsulated o-rings. 

Labyrinth seals are a type of dynamic mechanical clearance seal that, when the right material is chosen, exhibit very low friction and provide a long seal life. They are most often used to isolate an area of low pressure from an area of high pressure and do an excellent job of keeping problematic contaminants out and fluid media inside. Labyrinth seals perform extremely well in the presence of extreme pressures as well as cyclic temperatures and pressures. They are also available in a wide variety of engineering polymers, including those recommended for semiconductor seals.

Spring-energized seals can handle vacuum pressures and extreme temperatures extremely well, maintaining a reliable seal when lip seals or o-rings fail. This is made possible by a spring energizer that causes the lip of the seal to maintain contact with the sealing surface even when there are varying pressures or dimensional changes. These are highly dependable seals and can work well in semiconductor applications when combined with the right spring and lip material. 

Encapsulated o-rings work especially well in cryogenic applications and are able to maintain seal integrity in axial sealing applications that are extremely challenging to other seal types. In this type of seal, an elastomeric or spring core is completely contained within a polymeric o-ring, and (once again) with the right material choices can provide outstanding performance even in the presence of highly corrosive or reactive materials. In addition, non-contaminating materials such as PTFE are often used in encapsulated o-rings.

Polymer Materials for Semiconductor Seals

While the type of seal used (i.e., labyrinth, spring energized, etc.) is vital to your design, the choice of material is vital to ensure that the seal does not degrade or prematurely fail. There are several engineering polymers that are well adapted to the unique challenges faced by seals in a semiconductor environment.

PEEK (Polyether Ether Ketone) already has an excellent reputation as a seal material for general applications due to its low friction, wide range of operating temperatures, and excellent chemical resistance. In the context of seals for semiconductors, it also exhibits key features such as low outgassing, good plasma resistance, and excellent performance at high-service temperatures. 

PTFE (Polytetrafluoroethylene) is another very popular seal material, sharing several characteristics with PEEK along with even lower friction and superior chemical compatibility. PTFE works extremely well in high temperature, corrosive environments and is a high-purity material. Note that PTFE is already a commonly used material for gaskets in semiconductor applications.

PI (Polyimide) is another excellent option for semiconductor seals. It is another high purity material that exhibits low outgassing and excellent cryogenic performance along with other properties that are needed to ensure excellent seal integrity. 

Another potential material for use in sealing applicants for semiconductors is PCTFE (Polychlorotrifluoroethylene), often known by its trade name Kel-F or Neoflon. PCTFE shares many of the characteristics of PTFE while improving on others, including better strength and hardness. Like PTFE, it also offers low friction and excellent chemical compatibility.

PAI (Polyamide-imide), referred to by its trade name Torlon, is another option when looking for the right material in semiconductor sealing applications. It is another polymer that has excellent sealing properties when cryogenic temperatures are involved and high pressures are involved. It is also chemically compatible with a range of corrosive media and has excellent wear resistance combined with self-lubrication and low friction. 

Conclusion

Specifying seals for semiconductor applications can be extremely challenging, but the right combination of seal type and material can increase operational efficiency, reduce equipment and process downtime, and lower overall maintenance and operation costs. If you are interested in further exploring sealing solutions for semiconductor applications, our knowledgeable team of seal experts here at Advanced EMC can work with you to find the optimal seal for your design.

PTFE Ball Valve Seats
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

The Basics of Ball Valve Seat Materials

Ball valves play a critical role in controlling the flow of fluid and pressure within a pipeline, but their effectiveness and safety is only as good as the seat material used. In this blog post, we are going to review the basics of five commonly used ball valve seat materials.

Ball Valves

Whether found in a petrochemical application where a leak could be environmentally devastating, or in a pharmaceutical laboratory where cleanliness and sanitation are critical, ball valve seats must be reliable and robust. A ball valve consists of the body of the valve, the body cap, the stem, the hollow ball, and the round ball valve seat. 

The ball valve seat is responsible for sealing the fluid inside and uniformly distributing the seating stress. In soft seat ball valve designs, either an elastomer or polymer is used as the seal and are inserted into a metallic seat ring. This approach, as opposed to hard seat ball valves, is popular because it provides good sealing action, is lighter weight, and more cost effective. 

Key Properties of Ball Valve Seat Materials

When choosing a polymer material for a ball valve seat, there are numerous factors that are involved. Key material properties include …

  • Sufficient ductility to provide a reliable seal
  • Dimensional stability to ensure the ball valve seat retains its shape for reliable sealing and performance
  • Very low friction to keep stem torque at a minimum
  • Low coefficient of thermal expansion so that the ball valve seat retains its shape when temperature changes occur
  • Excellent wear resistance for a long service life
  • Chemical compatibility with all media involved 

In some operating environments, it is also important that ball valve seat materials exhibit these properties:

  • Low moisture absorption to prevent dimensional changes in the presence of water or high humidity
  • Maintain performance with repeated sterilization that can include hot water, steam, and harsh cleaning chemicals
  • Good performance in the presence of sudden decompression (i.e., pressure drops over 650 psi)

Recommended Materials for Ball Valve Seats

There are several materials that work well as ball valve seats, including acetal, PEEK, PTFE, TFM, and UHMW-PE.

Acetal Ball Valve Seats

When aggressive environments are involved, Acetal (also known as Delrin) is often used. Acetal provides excellent wear resistance, is very rigid, has good toughness, and is resistant to cold flow. Although its operating temperature range is not very wide (-70°F to 180°F), it can handle pressures up to 5,000 psi. Acetal also works well in radioactive environments  but should not be used with oxygen flow.

PEEK Ball Valve Seats

PEEK offers excellent chemical resistance, very low friction, self-lubrication, and is flame retardant while also possessing a wide operating temperature range (from -70°F to 550°F). It can handle very aggressive applications and works well when there is a need for hot water and steam exposure–but does not do well in the presence of sulfuric acid.

In addition, PEEK is very well adapted to nuclear applications and is available in FDA-approved grades as well as filled grades with improved wear properties and better thermal conductivity. Note that PEEK is usually chosen for ball valve seats when the operating temperature range is outside that of PTFE.

PTFE Ball Valve Seats

PTFE (also known by its trade name, Teflon) has many of the same properties as PEEK, but involves even lower friction, dry running capabilities, and more extensive chemical compatibility. Like PEEK, it is available in FDA-approved grades and can handle cryogenic temperatures down to -50°F and high temperatures up to 550°F as well as pressures up to 5,000 psi.  \

Also like PEEK, PTFE can continue to perform even when repeatedly exposed to hot water and steam. Keep in mind, however, that PTFE does not perform well in the presence of fluorine or alkalies. PTFE is also very easy to clean and available in glass or carbon-reinforced grades that can provide improved wear characteristics, less propensity to cold creep, and lower thermal conductivity. 

TFM Ball Valve Seats

TFM (sometimes referred to by the brand name Dyneon) is a second-generation PTFE material that combines the best properties of PTFE (low friction, chemical resistance, high-temperature performance) with better stress recovery and the ability to handle higher pressures. It is also more elastic and resilient than PTFE. The operating temperature of TFM ranges from -100°F to 450°F and it is well adapted to applications involving steam and thermal fluids.

UHMW-PE Ball Valve Seals

UHMW-PE, which stands for Ultra-High Molecular Weight Polyethylene, has a low coefficient of friction, an operating temperature ranging from -70° F to 200°F, good chemical resistance, good dimensional stability, and good abrasion resistance. In general ball valve seats made from UHMW-PE can handle pressures up to 1,500 psi and can handle low to medium levels of radiation exposure.

Conclusion

Ball valve seals are used in many different industries, including chemical processing plants, oil and gas operations, manufacturing facilities, food preparation, and even residential use. As a leak-proof means of pressure and flow control, their smooth and reliable operation is critical–which is why polymer materials work extremely well for ball valve seats. If you are in the market for a ball valve seat material, contact the experts at Advanced EMC. We can put our years of experience to work for you, helping you select the right material for your project.