MLCC Selection: Dielectric, DC Bias, Voltage and Package

MLCC selection starts with the capacitance the circuit needs at its actual operating voltage and temperature. Then check the dielectric, voltage rating, package, and mounting requirements. A nominal capacitance value alone does not establish whether a multilayer ceramic capacitor will work in the circuit.

For stable timing, filtering, or tuning, C0G/NP0 is often a suitable starting point when the required capacitance and size are available. X5R and X7R offer more capacitance in a compact package, but their effective capacitance changes with operating conditions. Murata's comparison of Class 1 and Class 2 ceramics explains this tradeoff.

Document the full manufacturer part number and the specification engineering approved. Procurement can then compare sourcing offers and proposed substitutes against the same requirements.

MLCC selection checklist: start with the circuit

Record the circuit requirements before comparing catalog rows. For a regulator output, use the regulator datasheet's capacitance and ESR requirements; for a signal path, identify how much capacitance variation the circuit can tolerate.

Use this list to narrow the options, then browse NTCHIP's Capacitors category. Keep the selection record alongside the BOM so a purchasing change does not silently change the circuit.

Choose the dielectric: C0G/NP0, X5R, or X7R

Choose the dielectric according to the circuit's allowable capacitance variation. C0G is a Class 1 temperature-compensating ceramic. X5R and X7R are Class 2 temperature designations; they describe a temperature range and permitted capacitance change under the specified test conditions.

These classifications are summarized in Murata's ceramic capacitor characteristics guide. Confirm the exact component specification and application restrictions.

The ±15% temperature characteristic is separate from the initial capacitance tolerance, such as ±10% or ±20%. It also does not describe total capacitance loss under DC bias.

X7R alone does not tell you how much capacitance remains at the operating voltage. To compare X5R and X7R candidates, confirm the local temperature range first, then review each part's characteristic data.

Check effective capacitance under DC bias

For Class 2 MLCCs, applied DC voltage can reduce capacitance substantially. The amount depends on the exact component. Murata's DC-bias explanation shows why the nominal value can differ from the value available in service.

Open the manufacturer's characteristic data for the full part number. Record the applied DC voltage, temperature, AC test amplitude, measurement frequency, and whether the curve is typical or guaranteed. A curve for a similar value or neighboring package is not sufficient evidence for the selected part.

A hypothetical 10 μF screening example

Assume a circuit requires at least 4.7 μF. For illustration only, suppose a 10 μF candidate retains 60% of its nominal capacitance at the selected DC voltage and temperature.

The tolerance calculation assumes the retention factor can be applied to the low-tolerance unit. It is a screening assumption, not a manufacturer guarantee. These numbers are not measurements, a product recommendation, or an NTCHIP test result.

Hypothetical screening only: 10 μF × 0.60 × 0.80 = 4.8 μF. The assumed retention and tolerance factors do not establish a guaranteed minimum.

Aging and the full operating range still need review. If the manufacturer's model already includes a limit, do not apply it twice. Likewise, do not automatically multiply separate temperature and DC-bias percentage changes: their interaction is part-dependent, as discussed in Analog Devices' voltage and temperature investigation.

When combined-condition data is missing, request it or validate the candidate under the relevant conditions. A small positive result from a typical curve is not enough to release the part.

Select the voltage rating from the applied waveform

The voltage rating limits the conditions under which the component is specified to operate. It does not promise that a Class 2 capacitor retains its nominal capacitance at that voltage.

Check the voltage across the capacitor, including supply tolerance, ripple, startup, and transient conditions. Use the manufacturer's applicable DC, AC, pulse, and temperature guidance. A DC voltage rating cannot by itself establish suitability for an arbitrary AC waveform.

Choose design margin according to the component guidance and your reliability requirements. Apply any required derating to the conditions specified for that component. TDK's overview of ceramic capacitor characteristics distinguishes voltage rating from the other electrical characteristics.

A higher voltage rating may be a useful candidate filter, but it does not reliably rank effective capacitance. Compare the bias curves at your operating point before choosing between voltage ratings. ROHM's MLCC application note for buck converters includes examples where a higher-rated part has greater capacitance reduction.

Compare package size, height, and land pattern

Confirm whether a package code uses EIA/inch or metric notation. The same digits can describe different physical sizes under the two systems.

Murata's mounting guide documents these code pairs. Use the exact drawing for length, width, tolerances, and height; the code is not a complete mechanical specification.

Check the component drawing, recommended PCB land pattern, and maximum height. This conceptual drawing is not to scale.

A smaller case saves board area, but miniaturization can change the bias behavior. Height also matters: two capacitors with the same footprint can have different constructions and characteristic curves. If a candidate loses too much capacitance, evaluate a larger body and check its curve.

Check the recommended land pattern, soldering conditions, and the assembler's handling capability before accepting a package change. Ceramic bodies are vulnerable to mechanical and thermal stress. Consider board flex during depaneling, connector insertion, and screw fastening when reviewing placement.

For a board exposed to flexing, a suitable soft-termination series may reduce stress transferred to the ceramic. It still has specified limits. Murata's soft-termination explanation explicitly notes that excessive stress can still cause cracks. Record the termination requirement in the BOM if it is part of the design.

Check impedance, ripple, and regulator stability

For decoupling, compare the impedance over the frequencies the circuit needs to suppress. An MLCC includes equivalent series resistance (ESR) and equivalent series inductance (ESL), so its behavior departs from an ideal capacitor. Around self-resonance its impedance reaches a minimum; above that region, inductive behavior becomes significant.

Use the manufacturer's impedance data together with the PCB connection geometry. The nominal capacitance and package label do not fully describe the mounted decoupling network.

For regulator input or output capacitors, check the IC datasheet's permitted capacitance and ESR range. Some control loops require particular output-capacitor characteristics. ROHM's buck-converter note warns that changing to very low ESR can destabilize some earlier power-IC designs. Treat an electrolytic-to-MLCC change as a circuit review, even when the nominal capacitance matches.

Ripple current also produces losses and self-heating. Review the series' thermal guidance and check the assembled board at the relevant loads and temperatures. Record startup, load-transient, ripple, and stability checks required by the design owner.

Account for aging and measurement conditions

Class 2 ceramic capacitance can decrease with elapsed time. The change is commonly described against logarithmic time, and its rate depends on the material and product. Use the manufacturer's aging data and reference conditions when the circuit depends on a minimum capacitance over its service period. Murata explains this behavior in its capacitance-aging FAQ.

A specified heating process can reset this aging behavior, after which aging resumes. That does not repair physical damage or prove that old inventory is suitable. Keep storage, solderability, and electrical acceptance as separate checks.

If an incoming LCR measurement disagrees with nominal capacitance, first compare the test setup with the component specification. Check fixture correction, test frequency, AC amplitude at the component, DC bias, temperature, and the specified timing after thermal treatment. Murata's measurement guidance shows that insufficient applied AC test voltage can lower the measured value of a high-capacitance MLCC.

Distinguish a nominal-capacitance acceptance test from a test of effective capacitance under operating bias. Both may be relevant, but they answer different questions.

Review replacement MLCCs by evidence

Two parts described as “10 μF, X7R, 16 V, 0603” can differ in operating capacitance, height, termination, and application restrictions. Keep proposed alternatives separate from the approved BOM until engineering has reviewed them.

Record the outcome as reject, candidate for validation, or approved for the documented application. A catalog match supports screening; final approval needs the application evidence.

For example, a same-footprint candidate with no bias data should remain under review. A candidate with adequate published data may proceed to circuit validation. Approval should identify the application and revision so it is not later treated as permission for every use of that capacitor value.

Prepare the MLCC specification for sourcing

Send the approved manufacturer part number whenever it is available. If alternatives are allowed, describe the acceptance conditions and identify who can approve a change.

Include the following in the RFQ or its attached specification:

• Manufacturer, full part number, quantity, and required delivery date.

• Nominal capacitance, initial tolerance, dielectric, and voltage rating.

• Package convention, maximum height, termination, and packaging requirements.

• Minimum effective capacitance and the voltage, temperature, frequency, and aging conditions behind that requirement.

• Datasheet revision, characteristic data, and any application qualification requirements.

• Permitted alternatives, approval responsibility, and required traceability or inspection documents.

Attach curve data or the engineering selection record when a short BOM description would omit a critical condition. A supplier can satisfy a request for “10 μF X7R” while offering a part that misses the circuit's capacitance requirement.

For lifecycle or shortage-driven sourcing, verify the exact orderable number's status and any manufacturer change notice. Discuss storage history, packaging condition, date/lot information, and inspection needs where relevant. NTCHIP's quality-control information can support that discussion; the required documentation and inspection scope should be agreed for the order.

MLCC selection FAQ

Is X7R always better than X5R?

X7R covers a higher upper temperature limit: +125°C versus +85°C for X5R. Both have a ±15% temperature characteristic under the specified conditions. Choose using the actual temperature range and exact-part capacitance data; the code alone does not rank DC-bias performance.

Does a higher voltage rating mean less capacitance loss?

Not necessarily. Voltage rating and capacitance retention describe different properties. Compare the candidate curves at the voltage applied in your circuit. Do not approve a substitution solely because its voltage rating is higher.

Can a 10 μF MLCC provide less than 5 μF in use?

Yes. A Class 2 MLCC can lose enough capacitance under bias and other operating conditions to fall below half of nominal. The reduction depends on the exact part. Check its data before applying that expectation to another 10 μF capacitor.

Can I replace a 0603 MLCC with a 0402 part?

Treat it as a design change. Verify the package-code convention, land pattern, capacitance under bias, voltage and thermal limits, and assembly process. A matching nominal value does not establish electrical or mechanical compatibility.

Why does the capacitance meter show a low value?

Possible reasons include the test voltage, frequency, fixture setup, temperature, or aging state. Compare the measurement conditions with the component specification before judging the part. A low reading alone does not identify the cause.

Take a documented MLCC selection into the BOM

Choose the dielectric for the circuit's stability needs, verify effective capacitance at operating conditions, and check voltage stress and mechanical fit. Record the exact part and the evidence supporting its use before releasing a substitute.

Browse capacitors by category to review sourcing options. When the specification is defined, send an RFQ with the manufacturer, full part number, quantity, target date, and quality requirements. Availability, pricing, and lead time should be confirmed through RFQ.