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Chrome Oxide Green in MLCC: The Low-Sodium Grade Behind Reliable Capacitors

公開日 2026-09-01 · VERDECHROME アプリケーションノート · 読了約5分

A multilayer ceramic コンデンサ is a million microscopic sandwiches of barium titanate and nickel. The green powder that helps hold it together never appears on the BOM headline — but its sodium content decides how long the part lives.

THE PAIN — Insulation resistance that decays in the field. A コンデンサ that leaks current under bias years after it left the factory. The root cause is often invisible at incoming inspection: mobile alkali ions inside the 誘電体.

Where Cr₂O₃ Fits in the MLCC Recipe

Chromium oxide green has two well-established jobs in MLCC manufacturing. First, as an acceptor dopant in BaTiO₃-based 誘電体 ceramics: Cr³⁺ substitutes on the titanium site, compensating oxygen vacancies and suppressing the reduction of Ti⁴⁺ during base-metal-electrode (BME) firing in reducing atmosphere. The result is a 誘電体 that keeps its 絶縁抵抗 and resists DC-bias degradation.

Second, in the glass phase of terminal electrode pastes, where fine Cr₂O₃ tunes the softening point and thermal expansion of the glass so the end termination bonds to the ceramic body without cracking during co-firing.

The Sodium Problem

Failure mode	Mechanism	Root control
Insulation-resistance decay	Na⁺ migrates along grain boundaries under DC bias + temperature	Na₂O ≤ 50–100 ppm in all ceramic inputs
Accelerated capacitance aging	Alkali ions distort the space-charge layer at the grain boundary	ppm-level alkali in the raw Cr₂O₃
Firing defects	Alkali fluxing widens the 焼結 window unpredictably	Lot-to-lot chemical consistency

Sodium is the worst offender because it is small, monovalent and mobile. Under the DC bias a コンデンサ sees every second of its life, a sodium ion becomes a moving defect — every hop is 漏れ電流, and every hop ages the part.

What the Electronic Grade Spec Looks Like

This is why the DELIKEOXIDE EG-series exists. EG-99 delivers ≥99.2 % Cr₂O₃ with Na₂O ≤100 ppm; EG-99H tightens to ≥99.5 % and ≤50 ppm Na₂O, with iron ≤100 ppm, magnetic impurities ≤5 ppm and a D50 of 0.3–0.8 μm for homogeneous ドーピング in the barium titanate matrix.

Buying Checklist for MLCC Use

Ask for the sodium number. If the CoA does not state Na₂O, treat it as unspecified.
Check the iron and magnetic-im純度 line. Ferromagnetic particles create insulation defects in thin 誘電体 layers.
Specify the D50. Finer grades disperse more uniformly into BaTiO₃; coarser grades save cost where the paste only needs the glass tuning.
Demand lot consistency. MLCC qualification costs thousands of hours — the raw material must not drift.

THE WIN — A 誘電体 that keeps its 絶縁抵抗 through a decade of bias, humidity and thermal cycling, because the mobile ions were never allowed into the powder in the first place. That is what ppm means.

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よくある質問

ナトリウムはどう測定しますか？ 酸分解後の炎光光度法または ICP で測定し、Na₂O として全ロットの証明書に記載します。

EG-99 と EG-99H のどちらを？ データシートに ppm 表示が求められる用途、誘電体やスパッタリングは EG-99H。量産セラミック用途は EG-99 です。

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