Electronics Guide

Why Markings Are Terse

A marking has to fit on the part, survive assembly, and add almost nothing to the part's cost. Those limits explain why component codes are so compressed and why many small parts carry no marking at all.

Space, Cost, and Durability

Space runs out first. Bourns prints no marking on its CR-series thick-film chip resistors in the 01005, 0201, and 0402 sizes. In the 0603 size it marks 1 percent values with a three-character code instead of the four digits it uses on larger sizes. KEMET normally supplies its surface-mount multilayer ceramic capacitors unmarked. It offers laser marking as an extra-cost option, limits 0603 parts to the identifying letter K without a value code, and does not offer marking on C0G parts at all. Integrated circuits face the same squeeze: Texas Instruments marks its LMV321 operational amplifier in the five-pin SOT-23 package with the four characters RC1F.

A marking must also survive soldering, cleaning, and handling. The test list in Vishay Beyschlag's data sheet for its MBA, MBB, and MBE metal film resistors includes a solvent-resistance test in isopropyl alcohol, applied by the toothbrush method, whose requirement is that the marking stay legible with no visible damage. A marking that fails such a test is one of the signs inspectors look for when parts may have been remarked.

What a Marking Can Carry

A marking can state the electrical value, the tolerance, a rating such as voltage, the polarity or pin-1 orientation, the manufacturer, the part type, and the date or lot of manufacture. Small parts keep only the essentials. A marked chip resistor shows its value and nothing else. A KYOCERA AVX TAJ tantalum chip capacitor shows a capacitance code, a voltage letter, and a polarity band, and most of its case sizes add a logo and an identification code. A large aluminum electrolytic capacitor has room for nearly everything: Vishay BCcomponents lists the capacitance, a tolerance letter, the rated voltage, a date code, a factory code, the manufacturer's name, the upper category temperature, the negative terminal, and the series number among the markings of its 136 RVI radial capacitors, which carry them where possible.

A Code Points to a Specification

A marking rarely states everything that matters. The three characters on a chip resistor give its value but not its power rating, temperature coefficient, or maker. The full identity lives on the reel label and in the data sheet, so the surest way to keep parts identifiable is to keep them in labeled packaging until they are placed. Once a part has lost its packaging, its marking narrows the possibilities, and a measurement, the circuit it came from, or a data sheet settles the rest.

The IEC 60062 Marking Standard

IEC 60062, Marking Codes for Resistors and Capacitors, was prepared by IEC Technical Committee 40, Capacitors and resistors for electronic equipment. The current version, edition 6.1 of August 2019, consolidates the sixth edition of July 2016 with its December 2016 corrigendum and its amendment 1 of August 2019. Manufacturers cite it by name. Vishay Beyschlag's data sheet for its metal film resistors says that "four or five color code rings designate the resistance value and tolerance in accordance with IEC 60062," and Vishay BCcomponents marks tolerance letters and date codes on its aluminum capacitors "in accordance with IEC 60062."

The standard covers five subjects:

• Color codes for fixed resistors, including marking of the temperature coefficient of resistance (Clause 3).
• Letter-and-numeral codes for resistance and capacitance values, including the RKM code and three- and four-character codes (Clause 4).
• Letter codes for tolerance (Clause 5), for the dielectric material of plastic film capacitors (Clause 6), and for the temperature coefficient of resistance (Clause 7).
• Date codes suited to small resistors and capacitors (Clause 8).
• Two informative annexes: a special three-character code for resistance values from the E96 series (Annex A) and a special two-character code for capacitance values (Annex B).

IEC 60062 also states that its value, tolerance, and property codes "are intended for the marking of components, and are also suitable for the building of part numbers and component ordering codes." That dual purpose explains why the same codes reappear inside manufacturers' part numbers, as a later section shows.

The E Series Behind the Codes

The codes encode values from the E series of preferred numbers defined in IEC 60063, which IEC 60062 cites as a normative reference. The E24 series has 24 values in each decade, each with two significant figures, such as 4.7 and 6.8. The E96 series has 96 values per decade with three significant figures, such as 4.99 and 6.81. Two significant figures fit a three- or four-band color code or a three-digit code, and IEC 60062 limits its three-character resistor code to series up to E24. Three significant figures need a five-band color code, a four-digit code, or a special code such as EIA-96. Knowing the series also helps check a reading, because a decoded value that belongs to no E series often signals a misreading.

Resistor Color Bands

Color bands suit cylindrical leaded resistors, because a ring around the body can be read from any side. IEC 60062 defines one set of colors that serves four purposes: significant figure, multiplier, tolerance, and temperature coefficient. The position of a band decides which purpose applies. Resistors summarizes these codes alongside resistor construction and ratings.

Reading Direction and Band Widths

IEC 60062 sets three placement rules, and the first two tell a reader where to start. Wherever possible, the first band sits nearest one end of the body. The tolerance band is designed at least 1.5 times as wide as the other bands. And a band may be interrupted, provided that at least two-thirds of it is visible from any angle around the body. In practice, hold the resistor with its bands crowded toward the left, or with the wide band at the right, and read from left to right.

The two-letter codes come from IEC 60757, the IEC code for designating colors, and let a document name a band color in text. The unit 10⁻⁶/K is one part per million per kelvin, so a coefficient of ±50 in the table is ±50 ppm/K.

Gold, silver, and pink never stand for significant figures. If one of them turns up as the first band of a reading, the resistor is being read from the wrong end. Pink, which marks a multiplier of 10⁻³, entered the standard with the sixth edition in 2016, so charts based on earlier editions omit it.

Three, Four, and Five Bands

The number of bands follows the number of significant figures and whether the tolerance needs a band of its own:

• Three bands: two significant figures and a multiplier. The absent tolerance band means ±20 percent.
• Four bands: two significant figures, a multiplier, and a wider tolerance band, for tolerances tighter than ±20 percent.
• Five bands: three significant figures, a multiplier, and a wider tolerance band.

The Sixth Band: Temperature Coefficient

IEC 60062 permits color marking of the temperature coefficient of resistance (TCR) only on resistors whose value is coded with three significant figures, so a TCR mark always accompanies a five-band value code. The standard describes three methods: a solid sixth band, an interrupted sixth band, or another method that the resistor's documentation describes clearly and that cannot be confused with the first two. Its illustration of the last is a set of colored dots between the bands, for bodies too short for a sixth band. In every method the tolerance band remains the single wider band.

That last rule is a change. Earlier revisions of the standard made the sixth band the wide one, and the 2016 edition dropped the rule because users confused the wide TCR band with the tolerance band. A six-band resistor made to the older rule can therefore carry a wide band at the far end that does not give its tolerance.

A TCR band bounds how much the resistance may change with temperature. A red sixth band marks ±50 ppm/K. If that coefficient holds over the temperature range in question, the largest change in a 249 kΩ resistor warmed by 10 K is:

ΔR = 249,000 Ω × 50 × 10⁻⁶/K × 10 K = 124.5 Ω

That is 0.05 percent of the resistor's value, well inside its ±1 percent tolerance.

Common Reading Errors

• Reading from the wrong end. Use the wide tolerance band and the rule that gold and silver never come first. On a five-band part, a reversed reading often yields a value outside the E96 series. Read backward, the 249 kΩ example becomes brown, orange, white, yellow, and red, or 1.39 MΩ ±2 percent; 139 is not an E96 value, while 249 is.
• Confusing similar colors. Brown, red, and orange can look alike on small bands, and so can violet and gray. Use good white light and magnification.
• Mistaking an inductor for a resistor. Some cylindrical inductors carry color bands, as described under inductor codes below.
• Trusting the bands over a measurement. When a reading is doubtful, measure the resistor out of circuit. A result within a few percent of an E-series value usually settles the question.

Letter-and-Numeral Value Codes

Where a part has room for characters, printed codes replace colors. IEC 60062 sets the general rules. A value code uses three, four, or five characters: two, three, or four figures and a letter. The letter takes the place of the decimal point. The characters run together without spaces, and a tolerance letter may follow the value, with any further letters or numerals placed after the tolerance letter.

The RKM Code for Resistance

The RKM code takes its name from the three letters it first needed, R, K, and M, when it coded values from single ohms to a few megohms. The current standard uses five letters, and each serves as both multiplier and decimal point: L for 10⁻³ (milliohms), R for 1 (ohms), K for 10³ (kilohms), M for 10⁶ (megohms), and G for 10⁹ (gigohms). The letters are always capitals, even K, whose SI prefix is a lowercase k. Because every letter is a capital, milli cannot use m, which would collide with the capital M long established for mega, so the code uses L.

The notation resists a classic copying error. A decimal point can vanish from a faint print or a small font, turning 4.7k into 47k, but a letter in the middle of a number survives. Schematic Diagrams and Symbols shows the same notation on circuit drawings, where a lowercase k, as in 4k7, is common.

Fixed-Length Codes

Databases and ordering codes sometimes need every value to occupy the same number of characters. For values with up to three significant figures, IEC 60062 gives a fixed length of four characters, padded with zeros: R100 for 0.1 Ω, 1K00 for 1 kΩ, 10K0 for 10 kΩ, and 100K for 100 kΩ. Values with four significant figures should preferably take five characters, as in 59R04 for 59.04 Ω and 5K904 for 5.904 kΩ. Vishay Beyschlag writes the RKM style into its product descriptions, where 1K0 means 1 kΩ and 51R1 means 51.1 Ω.

Capacitance Values and Tolerance Letters

For capacitance, IEC 60062 defines a parallel scheme that it calls the multiplier code system for capacitors. On schematics and in parts lists the familiar forms are 4p7 for 4.7 pF, 4n7 for 4.7 nF, 100n for 100 nF, and 2µ2 for 2.2 µF, often written 2u2 where the Greek letter is unavailable. Any value code can take a tolerance letter, as in 4K7F for 4.7 kΩ with F tolerance, which Bourns and Vishay Beyschlag both use for ±1 percent. The tolerance letters are listed with the capacitor codes below, because they serve both kinds of part.

Numeric Codes on Surface-Mount Resistors

Chip resistors large enough to mark carry short codes of digits, sometimes with a letter. IEC 60062 defines a three-character code for resistance values from series up to E24, along with a four-character code system, and manufacturers choose among codes by value series and body size. Bourns's data sheet for its CR-series thick-film chip resistors shows a typical scheme.

Three- and Four-Digit Codes

• Three digits for E24 values. The first two digits are significant, and the third gives the number of zeros that follow. The code 103 means 10 followed by three zeros, or 10 kΩ.
• Four digits for E96 values. On the 0805 and larger sizes, the first three digits are significant, and the fourth gives the number of zeros. The code 4422 means 442 followed by two zeros, or 44.2 kΩ.
• R as the decimal point. Values that need a decimal point use the letter R, as in 4R7 for 4.7 Ω.
• A single 0 for jumpers. Zero-ohm jumpers carry the marking 0.
• No marking on the smallest sizes. The 01005, 0201, and 0402 sizes are unmarked.

Two traps catch new readers. A final digit of 0 adds no zeros, so the code 100 means 10 Ω and 1000 means 100 Ω. And the same digits mean different quantities on different parts: 101 marks 100 Ω on a resistor, 100 pF on a ceramic capacitor, and 100 µH on an inductor.

The EIA-96 Code

Bourns marks 1 percent values in the 0603 size with a three-character code that its data sheet calls EIA-96 marking. Two digits give the value's position in the E96 series, from 01 for 100 to 96 for 976, and a letter gives the multiplier. IEC 60062 describes a special three-character code for E96 resistance values in its informative Annex A, which offers guidance rather than requirements. The two tables below reproduce the Bourns version.

Three examples show the method:

• 10C: code 10 is 124, and C multiplies by 10², giving 12,400 Ω, or 12.4 kΩ. This is the example in the Bourns data sheet.
• 68X: code 68 is 499, and X multiplies by 0.1, giving 49.9 Ω.
• 01F: code 01 is 100, and F multiplies by 10⁵, giving 10 MΩ.

In the Bourns scheme, the form of a code identifies its system: two digits followed by a multiplier letter are EIA-96, and three or four digits, with R marking any decimal point, are the digit codes. Because the tables above reproduce one manufacturer's version, check the multiplier letters against the resistor maker's own data sheet whenever it can be found.

Capacitor Value, Tolerance, and Voltage Codes

Capacitors use more code systems than resistors do, because they come in more constructions and sizes. A large aluminum electrolytic capacitor prints its values in plain units, a tantalum chip uses a digit code and letters, and many ceramic chips carry no marking at all. Capacitors describes the types and their parameters.

The Three-Digit Picofarad Code

A common capacitance code has three digits and a base unit of the picofarad. As on resistors, the first two digits are significant and the third gives the number of zeros. KYOCERA AVX marks its TAJ tantalum chip capacitors this way, and its data sheet gives two examples: 106 is 10 followed by six zeros picofarads, or 10 µF, and 227 is 220 µF. The code 104, common on ceramic capacitors, works out as follows:

104 = 10 × 10⁴ pF = 100,000 pF = 100 nF = 0.1 µF

IEC 60062 defines both a picofarad-based and a microfarad-based three-character code, so a code on an unfamiliar capacitor should be checked against its maker's data sheet. Values below 10 pF need a fractional multiplier. KEMET's ceramic part numbers use 9 as the third digit for a multiplier of 0.1 and 8 for 0.01, so 229 means 2.2 pF and 508 means 0.5 pF. Vishay Beyschlag's resistor part numbers follow the same convention, with 9, 8, and 7 standing for 10⁻¹, 10⁻², and 10⁻³.

Tolerance Letters

A tolerance letter often follows the value code. IEC 60062 gives separate letter tables for symmetrical relative tolerances in percent, for asymmetrical relative tolerances, and for symmetrical absolute tolerances of capacitors. The letters below appear in KEMET's ceramic capacitor data sheets. Resistor makers use F, G, and J for the same percentages and D for ±0.5 percent (F and J at Bourns; D, F, G, and J at Vishay Beyschlag), and Vishay BCcomponents marks M for ±20 percent on its aluminum electrolytic capacitors "in accordance with IEC 60062."

The letter D shows why a tolerance letter must be read together with the part. On a small capacitor it means an absolute ±0.5 pF, and on a resistor a relative ±0.5 percent.

Voltage Codes

No single code covers voltage ratings. Parts with room print the rating in volts, and Vishay BCcomponents lists the rated voltage "in V" among the markings of its aluminum capacitors. Smaller parts use letters or digits that belong to one maker. KYOCERA AVX marks the rated voltage of its TAJ tantalum chips with a letter.

KEMET's ceramic chip part numbers code voltage with a single character instead: 9 for 6.3 V, 8 for 10 V, 4 for 16 V, 3 for 25 V, 6 for 35 V, 5 for 50 V, 1 for 100 V, 2 for 200 V, and A for 250 V. So A means 10 V on a KYOCERA AVX tantalum chip and 250 V in a KEMET ceramic part number, and J means 6.3 V to KYOCERA AVX but ±5 percent tolerance to KEMET. Decode a voltage letter only with the maker's own table.

Marked and Unmarked Ceramic Chips

KEMET's data sheets say that its surface-mount multilayer ceramic capacitors are "normally supplied unmarked." A customer can order laser marking, in which case two sides of the body carry a K identifying KEMET, followed by two characters that, according to KEMET, follow EIA-198 and give the capacitance. The letter gives the significant figures, and the digit gives a power-of-ten multiplier in picofarads, with 9 meaning 0.1. KEMET's own example, KA8, is a 100 µF part: A stands for 1.0, and 8 multiplies by 10⁸ pF.

The 24 capital letters cover the E24 series, and KEMET's table adds lowercase letters for intermediate values: a for 2.5, b for 3.5, d for 4.0, e for 4.5, f for 5.0, m for 6.0, n for 7.0, t for 8.0, and y for 9.0. IEC 60062 also describes a special two-character code system for capacitors in its informative Annex B. Because marking is optional and costs extra, keep loose ceramic chips in their labeled packaging. A chip that has lost its label can be identified only by measurement, and even then its voltage rating remains unknown.

Polarity Marks on Capacitors

Electrolytic capacitors are polarized, and their markings show which terminal is which. The two common families use opposite conventions, which makes this one of the most important markings to read correctly.

Aluminum Electrolytic Capacitors

Aluminum electrolytic capacitors usually mark the negative terminal. The Vishay BCcomponents data sheet for its 024 and 025 AMR axial capacitors lists a band "to indicate the negative terminal" and a plus sign "to identify the positive terminal," and the company's radial series list negative terminal identification among their markings. These parts are large enough for plain text, so the capacitance in microfarads and the rated voltage in volts are printed rather than coded.

Tantalum Capacitors

Molded tantalum chip capacitors mark the positive terminal. KEMET's T491 data sheet states that "the positive terminal is identified on the capacitor body by a stripe, plus, in some cases a beveled edge," and KYOCERA AVX labels the band on its TAJ chips as the polarity band for the anode, the positive terminal. KEMET also warns that solid tantalum capacitors "may be permanently damaged or destroyed if connected with the wrong polarity."

One Stripe, Two Meanings

A stripe on an aluminum electrolytic capacitor usually marks its negative terminal, while a stripe on a molded tantalum chip marks its positive terminal. An assembler who carries the habit from one part to the other installs the part backward. Check polarity against the outline drawing in the data sheet and against the polarity mark on the board silkscreen. Where the part itself carries a plus sign, the sign removes the doubt.

Inductor Codes

Inductors borrow the resistor codes but use the microhenry as their base unit. IEC 60062 does not cover them, because its scope is limited to resistors and capacitors, so inductor codes follow manufacturers' practice. Inductors and Magnetic Components covers the parts themselves.

Printed Codes

Bourns shows the typical marking of its SDR0604 surface-mount power inductors as the three characters 101, which match the inductance code in the part number SDR0604-101KL, a 100 µH part. The digits read like a resistor code in microhenries: 10 followed by one zero. Values below 10 µH use R as the decimal point, as in the Bourns part number SRR1260-2R4Y for a 2.4 µH inductor, while SRR1260-100M is 10 µH. The letter after the value code gives the tolerance, and one maker may assign the same letter differently from series to series: Y means ±30 percent in the Bourns SRR1260 series but ±15 percent in its SDR0604 series. Some inductors carry plain text instead of a code. Bourns laser-marks the inductance and tolerance on its 9130, 9210, 9220, 9230, 9250, and 9310 series, for example 6.8 µH and ±10%.

Color-Coded Inductors

Some cylindrical inductors are color coded and look much like resistors. Bourns documents two color codes for its inductors, both giving inductance in microhenries with the familiar digit colors, black for 0 through white for 9. Its EIA code uses four bands. Its MIL code, for cylindrical choke coils, places a silver identifier band twice as wide as the others near one end, followed by three inductance bands and a tolerance band. On small units, dots may replace the bands where specified, with a larger dot for the identifier.

An ohmmeter tells a color-coded inductor from a resistor. Across an inductor it reads only the DC resistance of the winding, which is usually far below the resistance that the same bands would indicate on a resistor.

Polarity and Orientation Marks on Semiconductors

A semiconductor installed the wrong way around seldom works and may be destroyed, so orientation marks matter as much as type codes.

Diodes

A band on a diode marks the cathode, the terminal through which conventional forward current leaves the diode. It corresponds to the bar in the schematic symbol. Vishay's data sheet for the 1N4148 diode in the glass DO-35 package gives the cathode band color as black, and Diodes Incorporated lists "Polarity: Cathode Band" for its 1N4148W in the surface-mount SOD-123 package. For an unfamiliar diode package, confirm the convention on the outline drawing. Diodes and Rectifiers covers the devices themselves.

Light-emitting diodes identify the cathode in ways that vary with the package and the maker, so the outline drawing in the LED's data sheet is the reference. A multimeter's diode-test range can usually confirm a diode's orientation, because it shows a forward voltage only when the positive test lead touches the anode. A meter whose test voltage is lower than an LED's forward voltage, however, shows an open circuit in both directions.

Integrated Circuits

Integrated circuits mark pin 1 with a dot, a dimple, a notch at one end, or a beveled edge, and package drawings show where the mark sits; Texas Instruments' drawings, for example, label a pin 1 index area. Pins on dual-row and four-sided packages are numbered counterclockwise from pin 1 when the package is viewed from the top. Ball grid arrays name each ball by a row letter and a column number, and the orientation mark sits at the corner of ball A1. Do not infer orientation from the direction of the printed text alone; use the index mark and the drawing. IC Package Types describes the package families.

Transistors

The body of a small discrete transistor gives no general clue to its pin assignment, because different parts in the same package, such as SOT-23, assign their pins differently. Identify the exact part from its marking code, then read the pinout from that part's data sheet.

Semiconductor Marking Codes

Packages with room carry the manufacturer's part number or a close abbreviation of it; Vishay's data sheet gives the type marking of its 1N4148 in the DO-35 glass package as V4148. Small surface-mount packages carry short codes that bear little resemblance to the part number.

Looking Up a Code

The data sheet is the authoritative source, but a data sheet can be found only once the part is known, and that is exactly what a marking code leaves open. Work from the clues that constrain the search most:

1. Identify the package from its size, lead count, and outline.
2. Identify the maker from the logo, if there is one, or from the equipment the part came from and the parts around it.
3. Search that maker's data sheets. Manufacturers publish codes in a marking section: Nexperia's data sheets have a "Marking" table, Diodes Incorporated's have "Marking Information," and Microchip's have "Package Marking Information." Texas Instruments gives a "Part marking" column in the packaging information at the end of its LMV3xx data sheet, for example.
4. If the maker is unknown, consult a compilation of marking codes gathered from many data sheets, and treat every match as a candidate to be confirmed against its own data sheet and, where possible, by measurement.

Why Short Codes Are Ambiguous

Each maker assigns its short codes independently from a limited set of two- to four-character strings, so the same characters can identify unrelated parts from different makers. Codes can also vary within one part type. Nexperia reserves a character for the manufacturing site, and Texas Instruments notes that where it lists several markings in parentheses, "only one part marking contained in parentheses and separated by a '~' will appear on a part." Treat a short code as a clue, not an identification.

Date and Lot Codes

Date and lot codes tie a part to the batch it came from. They let a manufacturer trace a failure to a production lot, let a buyer confirm that a reel's contents match its label, and sometimes mark a change in the product itself. Microchip's MCP6001 operational amplifier data sheet notes that parts "with date codes prior to December 2004 (week code 49) were tested to ±7 mV minimum/maximum limits," wider than the ±4.5 mV input offset voltage limits in its current specification table.

Manufacturer Formats

Semiconductor makers and some passive-component makers publish their own formats, which differ in how they count years, months, and weeks.

Two decoded examples show the method. A Diodes Incorporated 1N4148W marked T4 with the date code L9 carries a September 2024 date. A KEMET T491 capacitor with the date code 605 dates from week 5 of a year ending in 6, which could be 2016 or 2026.

IEC 60062 Date Codes

For resistors and capacitors, IEC 60062 standardizes date codes short enough for small parts. It offers three families: two-character codes for year and month, repeating on a twenty-year or ten-year cycle; four-character codes for year and week, either fully numeric or alphanumeric on a twenty-year or ten-year cycle; and a single-character code for year and month on a four-year cycle. The standard lists ISO 8601, the international standard for representing dates and times, among its normative references.

Reading Date Codes Safely

• Cycles repeat. KEMET's single year digit recurs every ten years, and letter codes recur on their own cycles: Diodes Incorporated's key assigns the year letter M to both 2001 and 2025. A date code therefore needs context, such as the part's introduction date or the age of the equipment, before it pins down a year.
• Week numbering differs. Microchip counts the week of January 1 as week 01, while ISO 8601 makes week 01 the week that contains the year's first Thursday, so the two schemes can differ by one week in some years.
• Lot and site codes matter too. Microchip's traceability code, the lot trace code that Texas Instruments may add, Nexperia's site character, Diodes Incorporated's assembly-site bar, and Vishay BCcomponents' factory code all record where or in which lot a part was made. Quote them in full when reporting a failure to a manufacturer.

Manufacturer Logos and Part Numbers

Logos

A logo identifies the maker, and knowing the maker narrows every other lookup. Brands change as companies merge, so an older part may carry a mark its maker no longer uses. KEMET's recently revised data sheets carry YAGEO Group branding, for example, and Vishay sells aluminum capacitors under its BCcomponents name and film resistors under its Beyschlag name. A logo that matches neither a maker's current marks nor its historical ones is a reason for closer inspection.

Codes Inside Part Numbers

Because IEC 60062 designs its codes for part numbers as well as markings, a part number often contains the codes a marking would carry, plus the ratings that a small body cannot show. KEMET's ordering example for a C0G ceramic chip capacitor is C1206C104J3GACTU.

Vishay Beyschlag's metal film resistor part number MBB02070C1001FCT00 works the same way. MBB0207 gives the type and size, 0 the variant, C a temperature coefficient of ±50 ppm/K, 1001 a value of 100 × 10¹ Ω = 1 kΩ, F a tolerance of ±1 percent, CT the packaging, and 00 the standard version. Its product description, MBB/SMA 0207-50 1% CT 1K0, states the same value in the RKM code.

A marking and an orderable part number are not the same thing, and packaging suffixes need not appear on the body. Texas Instruments' LMV321IDBVR on a 3,000-piece reel and LMV321IDBVT on a 250-piece reel carry the same marking, RC1F. Component Identification and Selection covers part-numbering systems more broadly, including JEDEC, Pro Electron, and manufacturer-specific schemes.

Markings and Counterfeit Parts

Markings are the first thing an inspector sees, so counterfeiters alter them. A remarked part is a genuine part whose marking has been changed to misrepresent its specification, date code, manufacturer, or quality grade. Markings are also where many counterfeits give themselves away. Signs worth checking at receipt include:

• A marking format that differs from the maker's documented format, such as a full part number on a package whose data sheet lists a short code.
• A date code that falls outside the period in which the part could have been made, or that does not appear on the reel or tube label.
• Inconsistent fonts, spacing, depth, or position between parts in one lot, or between the parts and a known authentic sample.
• Signs that the top surface was sanded, or coated over the original marking before new marking was applied, a practice called blacktopping.
• A marking that rubs off in solvent on a part whose genuine marking should be permanent.

No single sign proves a part counterfeit; a failed marking test, for instance, is evidence of remarking rather than proof of it. Counterfeit Component Prevention covers detection methods, including marking-permanency testing, and Incoming Inspection Strategies covers how receiving inspection checks part numbers, date codes, and lot codes against purchase documents.

Identifying an Unknown Part

Identifying a part from its marking combines everything above with measurement and with the circuit the part came from.

1. Record the marking exactly, under magnification and good light, including logos, dots, bands, and the orientation of each line of text. Photograph it before cleaning or testing the part.
2. Identify the package, count the terminals, and note any polarity band, bevel, or pin-1 mark.
3. Decide which code family applies. Bands on a cylindrical body suggest a resistor or an inductor; a short digit code on a chip suggests a resistor, capacitor, or inductor; and letters and digits on a multi-terminal package suggest a semiconductor marking code.
4. Use the circuit. The reference designator beside the part on the board, and the schematic if one exists, often identify the part outright.
5. Decode the value with the appropriate table, and check that the result is a plausible standard value: E24 for two significant figures, E96 for three.
6. Measure the resistance, capacitance, inductance, or diode drop that the code predicts, with the part removed from the circuit or with one lead lifted.
7. Confirm the identification against the data sheet: the package drawing, the marking section, and the pinout.

Tools and References

A magnifier or stereo microscope reads fine marking and reveals rework. A digital multimeter measures resistance and, on its diode range, finds junctions and their polarity. An LCR meter measures capacitance and inductance directly. Dedicated testers identify and characterize semiconductor devices, as Transistor and IC Testers describes, and Component Testing and Characterization covers bench measurement methods more broadly.

The references behind the codes are IEC 60062, edition 6.1, for resistor color codes, value codes, tolerance letters, and date codes; IEC 60063 for the E series of preferred values; IEC 60757 for the two-letter color codes; and manufacturers' data sheets, especially their marking, ordering-information, and packaging sections. Reel and tube labels complete the picture by giving the orderable part number that a body marking abbreviates.

Conclusion

Component markings compress identification into whatever space a part offers. For resistors and capacitors, IEC 60062 supplies most of the vocabulary: color bands for significant figures, multipliers, tolerances, and temperature coefficients; RKM and multiplier codes that put a letter where the decimal point would go; three- and four-character digit codes; tolerance letters; and date codes. Around the standard sit conventions documented in makers' data sheets, including EIA-96 resistor codes, voltage letters on tantalum chips, semiconductor marking codes, and most date-code formats.

Two rules follow from that division. Decode a standardized code with the standard's tables, and decode everything else with the maker's own data sheet. And identify the kind of part before reading its code, because 101 means 100 Ω, 100 pF, or 100 µH depending on the part, and a stripe usually marks the negative terminal of an aluminum electrolytic capacitor but the positive terminal of a tantalum chip. When a marking leaves doubt, measure the part; when a marking looks wrong, inspect the part more closely before trusting it.

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