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enter image description hereI was inspecting a PCB with a magnifying glass and noticed some of the light brown ceramic smd capacitors have 3 digit markings on them. Is there a "standard" of what these markings stand for? The first digit looks like a K with a line above it (K̄), and the other two digits are always a letter followed by a number. Example: K̄J4 or K̄A5

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  • \$\begingroup\$ Can you upload a picture? \$\endgroup\$ – winny Apr 10 '18 at 13:46
  • \$\begingroup\$ Can you add a clear, in focus photograph of them? \$\endgroup\$ – Colin Apr 10 '18 at 13:47
  • \$\begingroup\$ Probably manufactuerer dependent \$\endgroup\$ – Voltage Spike Apr 10 '18 at 20:27
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I am going to assume you didn't even google search. Before asking a question - try googling it. You'll be surprised at what you can find with 5 seconds to spare.

I googled K̄A5 and the first link is a Kemet PDF. http://www.kemet.com/Lists/ProductCatalog/Attachments/735/KEM_C1095_MIL-PRF-32535.pdf

Searching the document with again, the K̄A5, I find the following on page 12.

enter image description here

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  • \$\begingroup\$ When I posted this I thought it was an R instead of a K. Once I found a better magnifying glass and edited my post. I did find this same page then. My apologies. \$\endgroup\$ – jAce Apr 10 '18 at 15:28
  • \$\begingroup\$ @jAce no need to apologize! \$\endgroup\$ – efox29 Apr 10 '18 at 15:29
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See page 12 of this datasheet. In summary

KEMET MIL-PRF-32535 ceramic capacitors will be marked in accordance with the military specification on case sizes ≥ 0805. Case sizes below 0805 will not be marked. Two sides of the ceramic body will be laser marked with a “K̄” to identify KEMET, followed by two characters to identify the capacitance value.

The marking appears in legible contrast. Illustrated below is an example of an MLCC with laser the marking of “K̄A5”, which designates a KEMET device with the rated capacitance of 100 nF

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There are two common SMD marking schemes: three digit (e.g. 104) and letter+digit (e.g. A5). The last digit encodes the exponent, and the two first digits, or a single letter, encode the mantissa in picofarads. Two digits encoding is pretty straigthforward (they represent a number between 10 and 99), and the letter encoding is usually done according to the following table:

A   1.0     J   2.2     S   4.7     a   2.5
B   1.1     K   2.4     T   5.1     b   3.5
C   1.2     L   2.7     U   5.6     d   4.0
D   1.3     M   3.0     V   6.2     e   4.5
E   1.5     N   3.3     W   6.8     f   5.0
F   1.6     P   3.6     X   7.5     m   6.0
G   1.8     Q   3.9     Y   8.2     n   7.0
H   2.0     R   4.3     Z   9.1     t   8.0
                                    y   9.0

For example,

"104" -> 10 * 10^4 = 100000pF = 100nF
"A5" -> 1.0 * 10^5 = 100000pF = 100nF

Of course, there are different encodings out there, so check the datasheet from the manufacturer or measure the actual value to be sure.

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