Film Capacitors

The film capacitor market represents slightly over $2 billion globally. Within the $2b, the global market for paper and plastic AC film is approximately $1.4b while the paper and plastic DC film market is approximately $860m.

The overall film market is projected to see an increase of at least 5% in 2012. Many countries, such as the USA, China and Western Europe have instituted economic stimulus programs of which many have not been utilized. The growth from these untapped stimulus plans and the continued exploration into alternative energy, lighting, transportation and medical applications should provide the needed accelerant for the growth in 2012.

What are Film Capacitors?

Film capacitors are defined by their various dielectric properties and are utilized in almost every field of application.

The film capacitor, in its many shapes and sizes can range from a capacitance in the picofarads to high microfarads along with a wide spectrum of voltages depending on the dielectric film material.

Film capacitors are utilized for commercial and military applications meeting all DSCC approvals. They can be manufactured as surface mount components or have radial or axial leads. They can be machined, stamped, or have tabs or lugs. Film capacitors can be cylindrical in shape, box type or oval. They can be enclosed within a plastic or metal case. They come as a wrap and fill or in a hermetic or non-hermetic case. Film capacitors range in sizes from smaller than an inch to sizes of several cubic feet. They are identified by various family names, such as DC-Link capacitors, Snubber capacitors, EMI Suppression capacitors, Pulse capacitors, GTO capacitors, SMD capacitors, Metalized capacitors, Plastic capacitors, and Film capacitors. All of them spanning various temperatures, dissipation factors and operating life expectancies.

Applications

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Dielectrics

Within the film portfolio, they are broken out into various film dielectric properties. The most common film dielectric is polyester (Mylar). The other available dielectrics are polystyrene, polypropylene, polycarbonate, metalized paper and Teflon. Each dielectric has advantages and disadvantages which need to be considered when selecting a capacitor.

Polyester: Known as many different names, DuPont’s trade name is Mylar but other names associated with polyester are PET, PETE, and PETP. Polyester is used for non-critical applications and is usually lower in cost. Polyester dielectric is made by melting polyester resin and stretching it into thin, flat sheets. Polyester capacitors are known for its self-healing properties and high dissipation factor. Polyester capacitors have values from .01uF to above 10uF and at temperatures up to 125 °C.

Polypropylene (PP): Polypropylene capacitors are utilized for high-frequency and high current applications and have a very low dissipation factor over its entire range as well as over a wide frequency range. For AC capacitor applications, polypropylene is the most suitable dielectric since the dielectric constant and the low loss factor are largely independent of the temperature and frequency. They have a low moisture absorption and high insulation resistance and are available in values from 1uF to 100uF and temperatures up to 105 °C.

Polyphenylene Sulfide (PPS): Polyphenylene Sulfide is known for its low dissipation factor and very good heat resistance, a combination not found in other capacitors. PPS also has a low dielectric absorption as well as very low moisture absorption. Polyphenylene Sulfide capacitors are available to 150 °C. PPS has about the lowest temperature drift of film capacitors.PPS capacitors are a good substitute for polycarbonate film capacitors. The main drawback of this dielectric would be that only one source is able to manufacture this grade of film. (Toray in Japan)

Polycarbonate (PC): Polycarbonate film capacitors offer very low temperature dependency with a wide operating temperature range. They are known for reliability and stability over different environmental conditions, and low losses. They have a heat resistance to 125 °C. There is only one supplier who says they manufacture the polycarbonate currently after Bayer decided to discontinue. There are a few suppliers who still have polycarbonate dielectric available and will continue until their supply runs out.

Paper (P): Paper or ‘Kraft Paper’ is the oldest of the film capacitor dielectrics. The paper must be impregnated with epoxy, wax, oil, or another suitable impregnate. It is still popular for high voltage and AC rated capacitors operating at lower frequencies. Paper can also be wound with plastic dielectrics in combination dielectric capacitors.

Polyethylene Naphthalate (PEN): Another form of polyester, it has very good heat resistance. PEN has a high dielectric constant with a high dielectric strength that provides good volumetric efficiency for metalized construction. It is a great general purpose capacitor. PEN is available to 125 °C and is utilized in many film SMD capacitors.

Teflon (PTFE): Teflon is a DuPont trademark for a wide variety of fluorocarbon polymers. PTFE probably has the lowest leakage and lowest dielectric absorption. It has a very low dissipation factor along with a wide range of temperature (can get to 250 °C for some), low temperature drift and very good stability. PTFE is a good film capacitor for critical analog applications although more costly.

Advantages/Disadvantages

Capacitor type Dielectric used Features/applications Disadvantages

Polyester Film Capacitor
(PET,PETE, PETP)

Polyester

Smaller in size when compared to paper or polypropylene capacitors of comparable specifications. May use plates of foil, metalized film, or a combination. Maximum operating temperature of 125C.

Limited use in power electronics due to its tendency to have higher DF with increasing temperature and frequency.

Polypropylene Plastic Film Capacitors(PP)

Polypropylene

Has become the most popular capacitor dielectric. Extremely low dissipation factor, higher dielectric strength than polycarbonate and polyester films, low moisture absorption, and high insulation resistance. May use plates of foil, metalized film, or a combination. Film is compatible with self-healing technology to improve reliability. Usable in high frequency applications due to very low dielectric losses. Larger value and higher voltage types from 1 to 100μF at up to 440V AC are used as run capacitors in some types of single phase electric motors.

Maximum operating temperature of 105C

Polyphenylene Sulfide Plastic Film Capacitors
(PPS)

Polyphenylene

Similar to polycarbonate and a great substitute. Can withstand full voltage at comparatively higher temperatures. (UL temperature index of + 200C) Extreme capacitance stability from -55 to +85C, PPS is virtually flat over this temperature range with a ppm/C of only 7. Good for SMD capacitors

Above 100C, the dissipation factor surpasses that of a polycarbonate so it could run hotter than a PC in some AC applications, but can operate without degradation at higher temperaturesCost is usually higher compared to Polypropelene

Polycarbonate Plastic Film Capacitor(PC)

Polycarbonate

Superior insulation resistance, dissipation factor, and dielectric absorption versus polystyrene capacitors. Moisture pick-up is less, with about +/- 80 ppm temperature co-efficient. Can use full operating voltage across entire temperature range (-55°C to 125°C)

Maximum operating temperature limited to about 125°C.Only one supplier manufacturing.A few suppliers still have supply and will manufacture until it is gone

Polystyrene Capacitor

Polystyrene

Excellent general purpose plastic film capacitor. Excellent stability, low moisture pick-up and a slightly negative temperature coefficient that can be used to match the positive temperature co-efficient of other components. Ideal for low power RF and precision analog applications

Maximum operating temperature is limited to about +85°C. Comparatively bigger in size.

Metalized Plastic Film Capacitors

Polyester or Polycarbonate

Reliable and significantly smaller in size. Self-healing capability results in high withstanding voltage, high reliability

Thin plates limit maximum current carrying capability.

Polyamide Plastic Film Capacitors

Polyamide

Operating temperatures of up to 200°C. High insulation resistance, good stability and low dissipation factor.

Large size and high cost.

PTFE Fluorocarbon (TEFLON) Film Capacitors

Polytetra- fluoroethylene

Lowest loss solid dielectric. Operating temperatures up to 250°C, extremely high insulation resistance, and good stability. Used in stringent, mission-critical applications

Large size (due to low dielectric constant), and higher cost than other film capacitors. Limited to a film/foil winding construction

Polyethylene Naphthalate
(PEN)

Polyethylene

Similar to polyester. Good heat resistance. Excellent for bypassing, signal coupling and filtering applications. Operating temperature to 125C

High dissipation factor

Manufacturing Process

The beginning process of a film capacitor starts with the resin. The resin comes from a limited number of suppliers in the world; DuPont, Teijin, Toray, Mitsui, Borealis and a couple of others. The dielectric grade resin is a small part of their overall market portfolio. Other markets served consist of producing film for Construction, Photovoltaic, Health Care, Security, Packaging and more. The resin is manufactured in large batches only a few times a year. Although capacity is available if the demand growth out performs the amount produced in the initial batches, procurement could be limited. The resin will go to a converter such as Toray, DuPont, Teijin, Steiner, or Treofan. The film dielectric grade is a small segment of a converter’s overall business so they will collect the demands and run large batches of coating a few times a year. For a specialty film coating, these could be run only once or twice a year. The converter, like the resin supplier must have insight into the visibility of demand. This is a valuable piece of their business as they must be able to place orders in advance of coating runs. The next stage is the metallizer. Unlike the resin supplier or the converter, film metallization is the core business of a metallizer. It is important for the metallizer to have as much as 6-12 months visibility depending on the film type. The amount of coating runs or available film can dramatically affect the metallizer’s business.

Film capacitors are manufactured by acquiring the film material from an approved source and integrating it with the desired electrode. Film/foil capacitors consist of two metal foil electrodes made of aluminum foil or tin separated by a piece of plastic film.

Metalized film capacitors differ than film/foil capacitors as the aluminum foils are replaced by a layer of metal vacuum deposited onto the film itself. The metal layer is usually aluminum, zinc or a combination and is a very thin layer.

Supply Chain and Availability

The industry has historically operated with an inventory buffer to help smooth out any increases and minimize lead time swings. With the last down turn, inventories were depleted and have not been replenished. The current demand exceeds the historical demand baseline. The key going forward will depend upon forecast accuracy. It is important for the resin and converters to understand the growing demand for film in our electronic components and allow for flexibility within their organizations to shift amongst divisions where the analysis of risk verse reward can help minimize lead times.

In 2010 and 2011, many manufacturers increased their production area for film capacitors. With the additional capacity, we are beginning to see the lead-times come in and the quoted lead times of 50+ weeks have past. You should expect to see standard film capacitors have deliveries of 8-12 weeks. Some of the box type, 5mm film capacitors will still be extended but level off in the 18-20 week timeframe.

As for pricing, the demand and the availability of the film and foil along with the continued swings of raw material costs will be the determining factor. I believe our pricing should remain stable for at least the next six months (mid 2012).

For your film capacitors, TTI is an authorized distributor for AVX, CDE, KEMET, Nichicon, Panasonic, TDK/EPCOS, Surge/Lelon, UCC, Vishay and Wima. To order, please contact us at 1-800-CALL-TTI or visit us online at www.ttiinc.com.

Acknowledgements:

I would like to thank the following companies and organizations:

All of TTI’s franchised Suppliers: AVX, CDE, KEMET, Nichicon, Panasonic, TDK/EPCOS, Surge/Lelon, UCC, Vishay and Wima whose websites are accessible via www.ttiinc.com

Dennis Zogbi; Paumanok Publications, Inc. Industrial Research Division, Passive Component Industry Magazine, Sept 2010

Chris Reynolds; AVX Corporation, Film Technology Extends Lifetime in Green Energy Applications, ECN, February 2011, www.ecnmag.com

Pietro Andreetti, Andrew Bellavia and Geoffrey Imlach; KEMET training, November 2011

APEC- Applied Power and Energy Conversion Conference- 2011, Special Session 1.3.4- Polymer Film Capacitors, March 2011

Global Sources Electronic Components, New Energy Buoys Capacitor Industry, September 2011, www.globalsources.com

EFY Enterprises; www.electronicsforu.com

Semec; www.semectech.com/Film-capacitors

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