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Polystyrene (PS), Polyphenylene Sulfide (PPS), Teflon (PTFE) and Polysulfone (PSU) film capacitors

This article is the last part of a complete installment on the construction, application, and features of film and foils organic dielectric capacitors, divided into 6 sections:

Introduction to film capacitors
Evolution and applications of paper capacitors
Polyester PET /KT/MKT capacitors
Polypropylene PP / KP / MKP capacitors
Polycarbonate PC /KC/ MKC capacitors
Polystyrene (PS), Polyphenylene Sulfide (PPS), Teflon (PTFE) and Polysulfone (PSU) film capacitors

Polystyrene (PS) is a non-polar dielectric material that, like polycarbonate, has been replaced by polypropylene to a great extent. However, its availability is strongly limited due to ceased production.

Polyphenylene Sulfide, or simply PPS, has become a popular material mainly because of its relatively high temperature resistance, which allows SMD manufacture.

General Comments to PS

ε_r ≈ 2.4. Max. temp.+70°C (possibly +85°C). Smallest film thickness 4 μm (0.16 mils). Except for metal foils, often double metalized plastic foils are used.

Advantages

Very low losses: 0.01% at room ambient and 1 kHz.
Very high IR; RC 200 000 s. More exterior factors determine the IR than the material itself.
Dielectric absorption 0.02%.
Stability ΔC/C, max ± 0.5%.

Disadvantages

It can be metalized due to high carbon deposits and too little oxygen at a self-healing breakdown.
Chemically sensitive film.
Availability is limited due to ceased production.

Temperature and frequency dependencies for PS

Figure 40. Capacitance versus temperature for PS capacitors.

Figure 42. Typical curve range for Tanδ versus frequency for PS capacitors.

Figure 41. Tanδ versus temperature for PS capacitors.

Figure 43. Typical curve range for IR versus temperature in PS capacitors, when C ≤0.1μF.

General comments to PPS

Foil types exist, but the metalized design is a rule. If nothing else is said, metalized film applies.

ε_r ≈3.0. Max. temp.+140 °C; most manufacturers recommend a maximum of +125 °C. Dielectric absorption ≈ 0.1%.

The smallest film thickness is 1.2 μm (0.05 mils), but former quality problems with the thinnest film may cause stronger derating of the lowest rated voltage. However, the supply of film is stabilized, thus indicating an established demand…

The film is used in capacitors both for lead mount and SMD. Existing chip types are made in a stacked design.

Temperature and frequency dependencies for PPS

Figure 44. Typical curve range for capacitance versus temperature in PPS capacitors.

Figure 45. Typical curve range for capacitance versus frequency in PPS capacitors.

Figure 46. Typical curve range for Tanδ versus temperature in PPS capacitors.

Figure 47. Typical curve range for Tanδ versus frequency in PPS capacitors.

Figure 48. Typical curve range for IR versus temperature in PPS capacitors.

Table 6. POLYSTYRENE (PS) and POLYPHENYLENE SULFIDE (PPS)

Other plastic, organic film capacitors used in special designs:

Teflon (PTFE)

Teflon exists both in metalized and foil designs. The greatest advantage of the film is its temperature resistance. On the other hand, the price is high, giving cause for exclusive hermetic designs.

Capacitance 470pF….4.3μF.
Tolerance ±0.25….±20%.
Temperature range -65/+200°C.
TC -200…+50ppm/°C.
Rated voltage 50…600 V DC.
Tanδ , @ 1kHz, 20°C, ≤0.1%.
IR, @ 20°C, foil ≥500GΩ/ ≥100 000s,
IR, @ 20°C, metallized film 50GΩ/ 10 000s.
Stability ΔC/C max -1%.
ε_r ≈ 2.2.
Dielectric absorption ≤0.02%.
Recommended derating 0.6xV_R.

Polysulfone (PSU)

Polysulfone capacitors belong to the same price group as one Teflon. They are used only in special applications where high-temperature capabilities and excellent characteristics are of vital importance. The capacitors have been manufactured only in hermetic design and with foil electrodes.