First, let's get our nomenclature straight. 1 mF (milli) = 10-3 farad, 1 uF (micro) = 10-6 farad. 1 nF (nano) = 10-9
farad, 1 pF (pico) = 10-12 farad. 1 pF = 10-3 nF =10-6
uF. Nano is rather less common than micro and pico, but it still shows up. "Femto farad " (fF) is used for things like RAM chip storage capacitors, but there are no discrete capacitors in that size range.
* these markings are not used consistently by manufacturers, which suggests they may not be sanctioned by the EIA.
It would be nice if there was more consistency to capacitor markings. If the manufacturer has lots of room (like on big electrolytics) they will
usually print everything they can; value, voltage rating, temperature rating, series, even country of manufacture. However, the smaller the part gets, the less information you get until, on the smallest parts
there may be nothing at all. On small through-hole ceramics, a two-number-plus-exponent system is often (but not always) used. This, like most marking systems, is based on the picofarad, the lowest common
denominator of capacitance. 470 may be 47 (47 x 100) or 470 pF but 471 is almost certainly 470 (47 x 101). 473 will probably be 0.0047. However, 479 will probably mean 4.7 (47 x 10
-1). Values below 10 pF may use "R" for a decimal point, 4R7 = 4.7 pF for example. With luck, you might also find the material (C0G, X7R, etc.) and voltage rating. The tolerance may be next
to the value. Table 5 shows the EIA tolerance codes for ceramic capacitors. Once again, don't expect to find all possible combinations of values, dielectrics, and tolerances. The tighter tolerances
mostly apply to small C0G capacitors and the looser tolerances to larger Class 2-4 ceramics.
For example, if you see .047K, the value is .047 uF 10%.
Some ceramic disks wear a color "skull cap" to indicate the dielectric. These will also use a XXM
format to indicate value (where the M is the multiplier), and a tolerance letter from Table 5 above. For example, 102J with a black cap would a 1000 pF 5% C0G. There is a similar system for Class 2 and 3 ceramics.
With European parts, you may also see capacitors marked with a two-digit system with the "multiplier"
letter used as a decimal point. For example, 4700 pF would be written as 4n7, which is 4.7 nanofarads. I understand this is taken from IEC 60062 (which I have not yet seen). Some examples are:
Some film capacitor manufacturers use a code that indicates the capacitor type. I have seen it referred
to as "European". A few manufacturers seem to follow this system exactly, while some others sometimes use it with variations. The table below is not complete.
More of these are at http://www.fust-electronica.nl . All this is little problem for equipment
manufacturers who know what they are buying. The hobbyist using surplus parts (or someone doing repairs) might at least want to invest in a cheap capacitance meter (or build one).
SMDFor example, A5 = 1.0 x 105 = 100,000 pF = 0.1 uF, and f9 = 5.0 x 10-1 = 0.5 pF. Simple enough.
SMD ceramics will often be marked with a two-digit EIA code (letter plus number) to indicate value.
You may also see a one-digit-plus-color-code. See Tables 10 and 11 below. Manufacturers usually offer
volume buyers three marking options, EIA standard, custom, and none. None is chosen all too often. Table 10 is an EIA system, but the origin of Table 11 is unknown (I have only seen it used by Philips).
The type of dielectric may be indicated with a "bar code" system that uses bars above, below, and on
either side of the value code. For example, |XX is X7R with value of XX from table 6 above, and XXI is Z5U. XX is N330 (S2H), XX is N470 (T2H), XX is N750 (U2J). C0G is
XX, where the bar is my way of indicating bars >over< the value digits (XX). So for example, |A5 is 0.1 uF X7R. Murata-Erie uses this system, but I donīt know if anyone else does..
X is N150
X is N220
- XX is N330
- XX is N470
- XX is N750
- |XX is X7R
- XX is Y5V
- XX| is Z5U
SMD tantalums usually have enough room to have the value and voltage spelled out (sometimes
without telling you which is which), some use the two-digit EIA code above, and some are marked in other ways. Tantalums can also be found with a voltage code (instead of the tolerance code normally seen on
ceramics), as shown in Table 12 below.
So how many ways can you mark a tantalum SMD capacitor? Any number of ways depending on
room available and the manufacturer's frame of mind. A 10 uF/25 Volt capacitor might look like:1 Military
2 X is the date code
3 Y is the tolerance
The above list is not exhaustive. Variations include date codes based on a system of dots, and special
voltage/value schemes loosely based on the EIA codes, but with modifications and additions. At least one
company sometimes uses the letter part of the EIA code, without the exponent, to indicate uF instead of pF (J would be 2.2 uF).
When it comes to polarity identification, tantalum manufacturers are totally fixated on the anode, either
with a stripe (either white on black body or black on light body), a "+", a sharp bevel, or some combination.
However, some SMD tantalums are so small they have no markings at all. In that case, the anode end is identified by allowing a nib of anode wire to stick through the anode termination. I donīt know of any
manufacturer who marks the cathode, but who knows?
Military capacitors use a long-winded code that gives dielectric, temperature drift, value, tolerance, temperature range, voltage, and failure rate. See
http://fcim.csdc.com for that and some other marking codes.
Obsolete Mica Codes
Molded micas (sometimes called "stamp" micas) came in cases with molded-in "pockets" for colored
paint dots that identified some combination of value, tolerance, voltage rating, vibration rating, temperature rating, and temperature drift.
MIL-C-5 used a 6 and 9 dot system to show value, tolerance, voltage, vibration rating, and
temperature drift. The voltage rating was determined by case dimentions when 6 dots were used. EIA RS-153 was a 5, 6, or 9 dot system very similar to MIL-C-5. The EIA system covered "button" micas as
well as stamp micas. Manufacturers have used a variety of proprietary 3, 4, 5, and 6 dot systems to show
value, tolerance and voltage. Eventually, some manufactures gave up the paint dots and just printed the numbers on the case, especially if the part didnīt fit the system (a 1/2% tolerance part for example).
http://www.flash.net/~billhar/capcode.htm Has the color codes for most of the manufacturerīs systems.
http://www.tpub.com/neets/book2/3g.htm Mica color codes.
Other Obsolete Codes
Someday, may be of interest to people repairing antique electronics. Molded paper capacitors once used a color dot system of the sort used by molded micas.
Additional sites with capacitor marking information.http://mile-high-www.cudenver.edu/callab
A collection of capacitor marking standards for older mica, ceramic, and paper capacitors.