Capacitors Blog

Silver mica capacitors, also known as silvered mica capacitors, rendered traditional mica capacitors obsolete. Instead of being clamped with foils these use sheets of mica coated on both sides with deposited metal. The assembly is dipped in epoxy. The advantages are:

1.greater stability, since there are no capacitive airgaps that can change dimension

2.airtight enclosure removes the risk of oxidation or corrosion of plates or connections.

3.greater capacitance per volume, since

• there are no airgaps between plates and mica,
• the conducting surfaces can be thinner.
• no clamping mechanism is needed

Mica Capacitor Specifications：

Capacitance Range : 1pf – 22,000pf
Tolerance : ±0.5pf, ±1%, ±2%, ±5% ~ 20%
Rated Voltage : dc 50v, 100v, 300v, 500v
Operating Temperature: -55℃ ~ 125℃
Withstanding Voltage: rated voltage x 2 (vdc) within 1-5 seconds

Link：http://www.suntan.com.hk/pdf/Mica-Capacitors/TS23.pdf
Contact Email：info@capacitors.com.hk

Natural mica contains many other materials including, iron, sodium, ferric oxide, and lithium. Because of the variability in composition of natural mica, mica destined for use in capacitors must be carefully inspected and classified, which adds to the manufacturing cost. All varieties of mica are chemically very stable and inert. Mica does not react with oil, water, most acids, (the exceptions are hydro-fluoric and sulfuric acid) alkalis, and solvents.

Mica’s thermal, electrical, and chemical properties make for excellent capacitors. Capacitance change with temperature range from ± 500 ppm/°C to 50 ppm/°C, depending on the construction technique. Mica capacitors exhibit very little voltage dependence, with dC/dV less than 0.1%. Mica capacitors have high Q or conversely small power factors (range 0.0001–0.0004) that are quite independent of frequency. This, combined with low inductance designs, result in capacitors that are ideal for high frequency and RF applications. Specification sheets of mica capacitors commonly show parameters plotted into the gigahertz range.

There are many types of mica, but only six or so are common rock-forming minerals. Mica capacitors are normally made from muscovite mica, or potassium aluminum silicate, KAl₂Si₃O₁₀(OH)₂ . It is thermally stable up to 500°C, and has a high dielectric strength. Phlogopite mica, or potassium magnesium silicate, KMg₃Si₃AlO₁₀(OH)₂ , is softer than muscovite mica and has less desirable electrical characteristics, but it may be used up to 900°C. Mica deposits are found in Madagascar, Central Africa, South America, and India. India is probably the biggest supplier of mica.

Mica, a mineral, is one of the oldest dielectric materials used in capacitor construction. There are several kinds of mica, with differing properties, but mica is in general very stable electrically, mechanically, and chemically. It has a dielectric constant in the range 5–7. Mica has the interesting property that its crystalline structure is asymmetrical. The binding forces in one plane are quite strong, while the binding forces along the perpendicular plane are very weak. Because of this, it has a distinct layered structure, and it is possible to split or cleave mica into very thin, optically flat, sheets. For capacitors, mica sheets in the range 0.025–0.125 mm or even thinner are used.