Structure Basis of PFAAdvantages of PFAMolding and Processing of PFADifferent Forms of PFAApplication Areas of PFAFocus: PFA in Semiconductor ManufacturingPFA vs. PTFE: Correcting Common MisunderstandingsFAQs About PFA
Structure Basis of PFA
Perfluoroalkoxy alkane (PFA) is a very versatile fluoropolymer that comes from the same fluoropolymer family as PTFE (polytetrafluoroethylene).
PFA is a blend of tetrafluoroethylene (TFE) and perfluoropropyl vinyl ether (PPVE), the one fluorine atom in PTFE replaced by a perfluoroalkoxy group. Its carbon is hooked up to the oxygen and then the oxygen to some group like perfluoromethyl or perfluoroethyl.
PFA usually comes as particles or powders. It performs like polytetrafluoroethylene (PTFE), but it can be melted into thermoplastic resins, so it's also called meltable polytetrafluoroethylene.
Advantages of PFA
Because PFA has many advantages of PTFE and polyperfluoroethylene propylene (FEP), it is widely regarded as the best meltable fluorinated copolymer that can replace the two. Its basic characteristics can be summarized as follows:
- It has good flexibility and improves the melt viscosity of the polymer, so that it can be thermoplastic processed by general processing technology.
- The physical and mechanical properties of PFA at room temperature are similar to those of PTFE, and it can be used within the temperature range of its application.
- PFA's stress cracking resistance is significantly better than FEP.
- PFA is inert to almost all chemical reagents and solvents, and has little change when in contact with common acids, strong bases, redox agents, halogens or solvents. However, like other perfluorocarbon polymers, it will react with molten alkali metals and fluorine elements.
- PFA has good transparency. It is translucent when thicker and transparent in thin sheets. It has good weather resistance and atmospheric aging resistance and can be used outdoors for a long time.
- PFA has excellent dielectric properties, which are usually expressed as a constant that changes with temperature, but sometimes lower than those of PTFE and FEP.
Molding and Processing of PFA
Since PTFE is difficult to flow after melting, it can only be formed by sintering, which limits the processing methods and product design flexibility. On the contrary, PFA almost completely keeps the good physical properties of PTFE, coupled with good melt processing characteristics, which give the product such benefits as very low surface roughness and thus expand the use.
PFA has the melting point of 290~312°C, melt index of 0.8-30 g/10min and molding temperature 350~410°C. For PFA resin processing, we can use conventional compression, extrusion and injection molding processes.
Additionally, PFA is also injection, transfer molding, rotation molding, dipping, spraying and other processing to be produced as cables, tubes, sheets, films, coatings and other curved products and has almost all the applications in PTFE.
Processing Technology and Product Uses
| Processing method | Melt mass flow rate (g/10min) | Uses |
|---|
| Compression molding | 0.8~3.0 | Mainly used for pipes, pumps, valves, plates, tank linings, diaphragms, joints, some bearings, etc. |
| Extrusion molding | 3.1~6.0 | Mainly used for pipes, wire insulation layers, films and various electronic components. |
| Extrusion molding | 6.1~15 | Mainly used for extrusion processing raw materials, mainly used for cable insulation wires, multi-core cable sheaths, etc. |
| Injection molding | 16~30 | Mainly used in aviation, aerospace industry, chemical industry, and high-speed cable extrusion. More economical for some uses that do not require high stress cracking resistance. |
Different Forms of PFA
PFA is available in various forms, including:
Application Areas of PFA
- Chemical Processing: PFA is used in pipes, valves, fittings, and tanks for corrosive chemicals.
- Semiconductor Manufacturing: PFA can be found in semiconductor manufacturing processes, wafer carriers, etching chambers, chemical delivery systems.
- Medical Equipment Manufacturing: PFA is applied in medical equipment like catheters, tubes and implants.
- Food Manufacturing: PFA is used for food-processing machines, pipes, valves, and gaskets.
- Laboratory Instruments: PFA is used in beakers, flasks, tubing, etc.
Wafer shield PFA dipper
Focus: PFA in Semiconductor Manufacturing
Thanks to semiconductor technology, the transistor size has gone from 10m to 7nm, even 5nm, and the purity of chemicals is astronomical. Semiconductor producers pay careful attention to any skewed results due to contamination during manufacturing (traces of metals, organic matter, and particles). Parts fabricated with fluoropolymers of high purity allow semiconductor companies to keep cost low to develop cutting edge chips. Typical applications of PFA in key areas of semiconductor manufacturing include:
Transportation and Storage
PFA ensures the high purity of electronic chemicals during the manufacturing process, avoiding contamination of electronic chemicals due to dissolution and erosion of reaction containers, thereby reducing the defect rate of wafers.
Chemical Distribution System (BCD)
BCD is a system that can accurately distribute chemicals. This system usually includes fully automatic instruments for mixing and diluting chemicals. PFA is widely used in BCD infrastructure, including making ventilation pipes, valves, sinks, etc.
Wet Etching and Cleaning
In this process, PFA is made into various tools, such as flow meters, to ensure the high purity of etching liquid and cleaning liquid; and PFA is not easy to crack during use, thus ensuring the high efficiency of production.
Chemical Mechanical Polishing (CMP)
The liquid used in the CMP process is a grinding liquid containing fine particles. If the particles in the grinding liquid are too large, they will leave marks on the surface of the wafer, resulting in defects in the product. The filter made of PFA prevents impurities in the grinding liquid from contacting the wafer to a certain extent.
PFA vs. PTFE: Correcting Common Misunderstandings
- The biggest difference between them is that PFA can be melt processed, while PTFE cannot.
- PFA material has excellent stress cracking resistance and better permeation resistance than PTFE. Although PTFE has a more perfect molecular gap, PFA raw materials form a denser structure after melting.
- Which one is better, PFA or PTFE, in terms of bending life (i.e. the ability to withstand repeated folding)? It is impossible to determine! It depends on your specific product structure, bending radius, temperature environment, material selection and application.
- PFA can maintain strong mechanical strength and burst pressure at relatively high temperatures. However, in actual use, PFA's temperature resistance is not as good as PTFE. PTFE is superior in terms of lower water absorption and weather resistance.
- The dielectric constant of PFA is the same as that of PTFE, and the dissipation coefficient is very similar, but the dielectric strength of PFA is much stronger than that of PTFE. The dielectric strength of PFA is 3-4 times that of PTFE, and PFA is superior to PTFE in high-frequency (UHF/microwave) insulation.
- PFA can maintain strong mechanical strength and burst pressure at relatively high temperatures. However, in actual use, the temperature resistance of PFA is not as good as that of PTFE. PTFE is superior in terms of lower water absorption and weather resistance.
FAQs About PFA
Is PFA safe?
Yes, PFA is considered safe for use in a variety of applications. It is non-toxic, non-flammable, and does not release harmful substances.
PTFE and PFA, which one is more suitable for semiconductor industry applications?
The first fluoropolymer to hit the semiconductor space is PTFE, followed by PFA. While PTFE is currently more widely used than PFA in semiconductor manufacturing, in specific key areas, PFA is preferred to PTFE. It is difficult to say which one is more suitable for semiconductor applications because they are all indispensable. Howerver, we can offer some guidelines on what fluoropolymers to use for semiconductors from two sides of the issue.
PTFE parts are usually machined from compression-molded PTFE blanks and are used to process containers, accessories, connectors, transport containers and liquid transfer. PFA is more used in the semiconductor industry to manufacture pipes, valves, tees, containers, etc. In addition, some complex structural parts and products that cannot be machined using PTFE can also be manufactured using PFA by molding. For fluid handling applications, PFA components can be manufactured by non-contact welding, thus avoiding contamination of the original molded parts.
In terms of cost, PTFE generally has a lower initial cost, especially for small batches or simple shapes, because it does not require mold tools. For large-scale production or complex parts, PFA is more cost-effective due to its efficient manufacturing process. Initial tooling costs can be offset by lower unit production costs over time.
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