• Point
Modern board-level designs rely on multilayer ceramic capacitors for compact decoupling and filtering; understanding their in-circuit value is critical.
• Evidence
Datasheet trends and independent lab sweeps commonly show X7R 0603 1 nF, 100 V parts losing substantial capacitance under bias and temperature stress.
• Explanation
This note quantifies expected DC-bias and thermal behavior, outlines a reproducible test protocol, and gives practical mitigation so engineers avoid surprises when MLCCs operate away from 0 V / 25 °C.
Background & Key Specs Overview
Point: Start by listing the key nominal parameters that drive bias and thermal response. Evidence: For the class discussed, baseline values are package 0603, nominal capacitance 1 nF (1000 pF), rated voltage 100 VDC, tolerance ±10%, dielectric X7R, and an operating range typically spanning -55 °C to +125 °C. Explanation: These fields—capacitance, tolerance, rated voltage, temperature range, dielectric type and size code—should be captured from the datasheet and labeled as “datasheet nominal” vs measured.
Part number & package baseline
Record the part identifier and baseline numeric specs before testing. For a typical example part number, the nominal list defines the measurement targets. Mark values as “nominal (datasheet)” and reserve a separate column for “measured at 25 °C / 0 V” for BOM reviewers.
Why X7R dielectric matters
X7R is higher-permittivity but non-linear. EIA Class II dielectrics trade absolute stability for compact capacitance. Designers must expect moderate stability with notable voltage and temperature derating versus C0G/NP0.
DC-Bias Behavior: Expected Capacitance vs Voltage
Capacitance typically falls as DC-bias increases in X7R MLCCs. The curve shape is a steep initial drop at low-to-moderate voltages, transitioning to a slower asymptotic tail approaching the rated voltage.
| DC Bias (V) | Normalized Capacitance (%) | Visual Retention Guide |
|---|---|---|
| 0 V | 100% |
|
| 10–20 V | 85–95% |
|
| 25 V | 80–90% |
|
| 50 V | 60–75% |
|
| 100 V | 45–60% |
|
Circuit Implications: An RC low-pass’s cutoff frequency scales inversely with capacitance; a 40% reduction raises fc by 1/0.6 ≈ 1.67×. Recalculate filter poles and transient budgets using measured retention.
Thermal Stability
X7R typically varies within its class tolerance over -55 °C to +125 °C. Report checkpoints at -55, 0, 25, 85, and 125 °C. Largest shifts usually appear at temperature extremes.
Combined Effects
Assume multiplicative retention: If retention is 70% at a given bias and 90% at a temperature, worst-case is 63% (0.7 × 0.9). Prefer direct combined-condition measurements when possible.
Measurement & Test Methods
Recommended Equipment
- • Precision LCR meter (1 kHz–100 kHz)
- • Low-ripple DC bias supply
- • Temperature chamber / Cold-hot stage
- • 4-terminal Kelvin connection fixtures
Test Sequence
- Baseline at 25 °C / 0 V
- Voltage sweep (0 V → Rated) at fixed temps
- Temperature sweeps at fixed bias points
- Log stabilization time & uncertainty
Selection Guidance
Suitable where space is premium and moderate derating is acceptable. Avoid in precision timing. Choose NP0/C0G for absolute stability or larger footprints (0805) to reduce DC-bias sensitivity.
Layout Checklist
- Apply voltage derating (design < rated)
- Parallel multiple MLCCs to recover capacitance
- Place capacitors close to IC power pins
- Document retention curves in BOM notes
Key Summary
- ✓ Measure normalized capacitance vs DC voltage; use checkpoints (0, 10, 25, 50, 100 V) to recalc RC poles.
- ✓ Report temperature % change vs 25 °C; assume multiplicative retention for worst-case planning.
- ✓ Mitigate with derating, parallel parts, or stable dielectrics; document all measured retention for reproducibility.
Frequently Asked Questions
+ How does 06031C102K4Z2A capacitance change under DC-bias?
Measured response: Expect a rapid initial capacitance drop with increasing bias, then a slower tail toward rated voltage. Practical answer: Use the normalized retention table as a starting point and measure n ≥ 5 units at your operating voltages to set design margins.
+ What measurement frequency should I use to evaluate DC-bias?
Answer: Choose frequencies matching the application—1 kHz for timing/AC coupling and 10–100 kHz for decoupling or switching supplies. Record retention at multiple frequencies if used across a broad spectral band.
+ How should I report and apply combined DC-bias and temperature results?
Answer: Prefer direct combined-condition tests (bias applied during temperature sweep). If unavailable, multiply independent retention factors conservatively and explicitly note uncertainty in the BOM.
