SMD Chip Inductors

SMD surface mount inductors can be easily placed by high‑speed pick‑and‑place machines and thus reduce assembly cost compared to through‑hole coils.

The SMD technology also supports a high level of miniaturization and downsizing of electronics, which makes SMD inductors the default choice in most modern designs.

SMD Multilayer inductors

If the wire windings on the outside of a conventional “coil” are mounted inside the coil body, the so-called multilayer SMD inductor (Figure 1. and 2.) is created.

The ferrite body magnetically shields the component, significantly reducing external interference and cross-talk. The multilayer inductor may be seen as a “compromise” between the ceramic inductor and SMD ferrite. This component is especially suitable as an inductor in filters and resonant circuits where low interference from external signals is required and in circuits with high packing density.

In addition, multilayer inductors offer very good repeatability of inductance values and parasitics thanks to the printed, photolithographic manufacturing process, which simplifies filter and impedance matching design compared to hand‑wound constructions.
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Practical tips:

• Do not operate close to the self‑resonant frequency range, because the component’s behaviour changes from inductive to capacitive and Q collapses.
• Observe max. current loading capacity
• Low DC resistance, therefore also suitable for low-voltage systems

Power Multilayer Inductors

The miniaturization of SMD components, especially inductors, is a widespread trend in portable devices, as it is especially storage chokes that frequently require the most space. Wired components are out of the question in these orders of magnitude. This is where the power multilayer types (Figure 3.) apply.

In order to allow minimization of the coil volume, the switching controller IC is driven at ever-higher switching frequencies. Switching controllers like the Micrel MIC2285 already work with 4 MHz. The dimensions of the storage chokes required can therefore be reduced by up to 90%. The compact power multilayer inductors in 1008 package (2.5 mm x 2.0 mm x 1.0 mm) not only offer high rated currents (up to 2.4 A), but also a lower DCR than comparable to standard multilayer inductors types.

Compared to discrete wire‑wound chokes with similar current capability, these multilayer parts trade some efficiency for a much smaller, fully shielded form factor that is better suited to densely packed handheld and wearables PCBs.

The saturation current of the power multilayer inductors (such as WE-PMIs) relates to the typical inductance drop of –30% from the zero current inductance. The rated current is defined for the common self-heating of DT = 40 K with respect to the ambient temperature.

The used NiZn core material allows the use of the power inductors WE‑PMI series up to 10 MHz. In practice, most designers operate such inductors well below this limit, typically in the 1–4 MHz range, in order to balance core losses, switching losses in the converter and achievable efficiency.

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SMD – Wire Wound Inductor /SMD RF Inductor

Wound inductors are available also in SMD packages (Figure 6.). Individual types may essentially differ in their mechanical construction. Whereas components as WE-GF in Figure 6. right is completely embedded in plastic and can therefore handle high humidity very effectively, the other types (WE-LQ – Figure 6. left) is in an open package.

It can therefore be loaded with higher currents at the same inductance in relation to its package volume. However, the open construction also exposes the winding and core to the environment, so moisture, contamination and mechanical handling must be considered, especially in high‑reliability or automotive designs.

In Figure 7. and 8. the layout of the SMD RF Inductor is shown graphically. A wire-wrapping surrounds a ferrite body. The special ferrite mixture faciliates a wide inductance spectrum despite the miniature ferrite core. For RF matching applications, these inductors are usually specified by their impedance and Q over frequency rather than purely by inductance at 100 kHz, so it is important to read the RF datasheet curves instead of only the nominal L value.

Selection and Application Guidelines

Modern SMD inductors span several construction types and core materials, each optimized for a specific frequency range and application domain. This section provides practical guidelines for selecting the right inductor for power, signal and RF designs, complementing the basic construction overview above and helping to bridge from catalogue choice to real‑world design‑in.

Overview of SMD Inductor Types

The table below summarizes the main SMD chip inductor families you typically encounter on the market.

The goal is not to list every product series, but to highlight how construction, shielding and package style map to typical use cases and design trade‑offs.

Inductor type	Typical construction / example	Frequency range	Typical use cases	Key advantages	Typical limitations
Multilayer signal	Screen‑printed ferrite, stacked ceramic body	kHz to low MHz	Filters, resonant circuits, bias chokes	Good shielding, small sizes, low cost	Limited current, lower Q, lower SRF
Power multilayer	Internal printed windings in ferrite body	100 kHz to ~10 MHz	DC/DC converters in portable devices	Very small footprint, shielded, low DCR	Lower Isat than comparable wire‑wound
Wire‑wound open (power)	Enamelled wire on ferrite core, open frame	100 kHz to a few MHz	General power chokes, point‑of‑load	High current, higher Q, low DCR	More EMI, less moisture protection
Wire‑wound molded / sealed	Wire on core fully molded/encapsulated	1 MHz to RF	RF chokes, matching, high‑rel designs	Good environmental robustness, shielding	Slightly higher DCR, larger package
Thin‑film / air‑core RF	Planar or wire‑wound on low‑loss cores	Tens of MHz to GHz	RF matching, impedance networks	Very high SRF and Q	Very low inductance, small currents

Core Materials and Frequency Range

Core material selection defines usable frequency band, losses and DC bias behaviour.

• Ferrite NiZn: Used in many multilayer and small power SMD inductors; suitable up to about 10 MHz for power applications and higher for small‑signal RF chokes.
• Ferrite MnZn: Higher permeability, used at lower frequencies, but with higher core losses at several MHz.
• Powdered iron / alloy / metal powder: Distributed air gap, good for power chokes with higher saturation current and better DC bias behaviour in the hundreds of kHz to low MHz range.
• Nanocrystalline / amorphous cores: Enable low‑loss operation in the MHz region for advanced chip inductors; see the dedicated article on nanocrystalline MHz cores.

In many real designs, the choice of core material is implicit in the inductor series you pick from a manufacturer catalogue. Understanding the underlying material behaviour, however, helps you to explain why some “equivalent” inductors run hotter or saturate earlier than others, even when their nominal L and current ratings look similar on paper.

Core material	Relative permeability	Losses at MHz	Saturation flux / DC bias	Typical application band
NiZn ferrite	Medium	Moderate at 1–10 MHz	Moderate	Power multilayer, small RF chokes
MnZn ferrite	High	Higher above ~1 MHz	Moderate‑high	Low‑frequency chokes, filters
Powdered iron / alloy	Low‑medium	Lower at power freq	High	Power chokes 100 kHz–1 MHz
Nanocrystalline	Medium‑high	Very low up to MHz	High	Low‑loss MHz chip inductors

Key Electrical Parameters for Selection

When selecting an SMD chip inductor, the following parameters are usually critical:

• Inductance (L): Sets impedance and determines filter corner frequency or energy storage.
• Saturation current (Isat): Current where inductance drops (often by 20–30%) due to core saturation; for many power multilayer series this is specified at about −30% from zero‑current inductance.
• Rated current (Irated): Current that causes a specified temperature rise (for example 40 K) above ambient.
• DC resistance (DCR): Drives conduction losses; especially important in low‑voltage supplies.
• Self‑resonant frequency (SRF): Above SRF the part becomes capacitive and should not be used as an inductor.
• Quality factor (Q): Relevant for resonant circuits and RF matching; higher Q means lower losses around the operating frequency.

For compact power supplies it is often necessary to iterate between these parameters: reducing DCR by going to a larger package or different series may increase SRF and current ratings, but also cost and footprint, while a high‑Q RF inductor might not tolerate the required DC bias current in a bias‑tee or choke role.

Table 3 indicates which parameters typically dominate for different application classes.

Application	L range	Priority parameters	Preferred types
Buck/boost DC/DC choke	0.22–10 µH	Isat, Irated, DCR, thermal behaviour	Power multilayer, wire‑wound power
Input/output EMI filter	1–100 µH	L, DCR, SRF, shielding	Multilayer, shielded wire‑wound
RF matching (VHF/UHF)	3–270 nH	SRF, Q, tolerance, temperature stability	Wire‑wound RF, thin‑film
Resonant LC filters (audio/IF)	1 µH–10 mH	L accuracy, Q, DCR	Wire‑wound, multilayer
Bias chokes / decoupling	10 nH–10 µH	SRF, impedance vs frequency, DC current	Multilayer ferrite, RF chokes

Practical Design‑In Guidelines

Quick Selection Example

For a 5 V to 3.3 V buck converter at 2 MHz and 1 A load, you would first choose a target ripple current (for example 30–40% of the output current) and compute the required inductance, which often falls around 1–2 µH.

Then search for power multilayer or small wire‑wound SMD inductors in 1008 or 1210 case sizes with approximately 1.5 µH, sufficient Isat and Irated (≥ 1.5 A and ≥ 1 A respectively), low DCR and an SRF several times higher than the 2 MHz switching frequency.

Finally, compare NiZn‑based multilayer options against metal‑powder wire‑wound chokes: multilayer parts minimize footprint and EMI, while wire‑wound types often offer higher efficiency at higher currents.

As a final sanity check, simulate the converter with realistic DCR and core‑loss estimates and then verify with bench measurements of ripple current, efficiency and temperature rise, adjusting the inductor choice if necessary.

Conclusion

The basic construction overview of multilayer and wire‑wound SMD inductors explains why different technologies exist, but successful design‑in requires a structured selection approach.

By classifying the inductor type, choosing an appropriate core material and frequency range, and then checking inductance, current ratings, DCR, SRF and Q against the target application, designers can converge quickly on suitable SMD chip inductors.

Power multilayer inductors are attractive where footprint and height are critical, while wire‑wound and advanced core technologies such as metal powder and nanocrystalline cores are preferred for the highest efficiency, current capability and MHz‑range performance.

Combined with the detailed articles on nanocrystalline cores, wear‑out mechanisms and nonlinear inductor characterization available on this blog, this overview gives designers a coherent, end‑to‑end picture of how to specify, select and validate SMD chip inductors for demanding applications.

FAQ

Reference and Further Reading

• SMD Inductors – Passive Components Blog
• Nanocrystalline Cores for Low‑Loss MHz Chip Inductors – Passive Components Blog
• Experimental Evaluation of Wear Failures in SMD Inductors – Passive Components Blog
• One‑Pulse Characterization of Nonlinear Power Inductors – Passive Components Blog
• Würth Elektronik – SMD Inductors (WE‑MI, WE‑PMI, WE‑LQ, WE‑GF and related families)