The leakage current of MLCC (multi-layer ceramic chip capacitor) is the core indicator for evaluating its insulation performance, and its normal range shows significant differentiation due to differences in dielectric type, operating voltage, temperature, capacity, and manufacturing process. The reasonable range of MLCC leakage current is systematically analyzed from four dimensions: technical principles, influencing factors, testing standards, and selection suggestions, combined with typical data and cases:
1、 Technical principle and definition of leakage current
1. The essence of leakage current
Physical mechanism: The leakage current (I2) of MLCC is mainly caused by ion migration and electron tunneling effects in the ceramic medium.
Ion migration: In high temperature and high humidity environments, alkali metal ions (such as Na ⁺, K ⁺) in the medium move towards the electrode, forming a conductive pathway.
Electron tunneling: Quantum effects cause electrons to cross dielectric barriers, especially in ultra-thin dielectric layers (<1 μ m).
Mathematical Model:
Ileak=K⋅Vα⋅e−β/T
Among them, K is the dielectric constant, V is the voltage, α is the voltage coefficient (usually 1<α<2), β is the temperature coefficient, and T is the absolute temperature.
2. Testing conditions for leakage current
Standard method:
Voltage: Rated voltage (V_rated) or DC bias (such as V_rated/2).
Temperature: 25 ℃ (normal temperature test) or 85 ℃ (high temperature test).
Time: Read the stable value 60 seconds after applying voltage (excluding transient current).
Key equipment: High resistance meter (measuring range 106 Ω~1016 Ω), resolution<1nA.
2、 Factors affecting leakage current and interval division
1. Medium type: determines the leakage current reference
Class I ceramics (C0G/NP0):
Leakage current range: 0.1nA~10nA (@ V_rated, 25 ℃).
Characteristics: Temperature compensation type, medium is barium titanate based composite oxide, with extremely low ion mobility.
Typical applications: RF circuits, precision oscillators.
Class II ceramics (X7R/X5R):
Leakage current range: 0.1 μ A~10 μ A (@ V_rated, 25 ℃).
Characteristics: High dielectric constant type, medium is zirconate/titanate composite material, with trace ion impurities present.
Typical applications: power filtering, coupling circuits.
Class III ceramics (Y5V/Z5U):
Leakage current range: 10 μ A~100 μ A (@ V_rated, 25 ℃).
Characteristics: Semi conductive type, medium made of barium titanate with rare earth elements added, high ion mobility.
Current situation: It has gradually been replaced by polymer capacitors and is only used in low-cost scenarios.
2. Working voltage: Voltage coefficient effect
Voltage dependence: Leakage current has a non-linear relationship with voltage (α>1).
Example: The leakage current of a certain X7R capacitor is 1 μ A at 10V, which may increase to 5 μ A at 20V (α ≈ 1.5).
Safety margin: The actual working voltage should be ≤ 80% V_rated to delay the aging of the medium.
3. Temperature: Thermal excitation effect
Temperature coefficient (β): Leakage current increases exponentially with temperature.
Example: The leakage current of a C0G capacitor is 1nA at 25 ℃ and may increase to 100nA (β ≈ 0.2eV) at 85 ℃.
High temperature applications: Low beta media (such as MgO doped barium titanate) should be selected, or the junction temperature should be reduced through heat dissipation design.
4. Capacity and Size: Balance between Medium Area and Thickness
Capacity impact: Large capacity capacitors typically require thicker dielectric layers or larger electrode areas, which may increase the leakage current path.
Example: For the same X7R medium, the leakage current of 10 μ F/6.3V (0805 package) may be 5 μ A, while 0.1 μ F/50V (0603 package) is only 0.5 μ A.
Size effect: Due to the thinner dielectric layer (<1 μ m) of miniaturized capacitors (such as 0201 packaging), the electron tunneling effect is more significant, and the leakage current may increase.
5. Manufacturing process: defect control
Purity of ceramic powder: impurity content<50ppm, reducing ion migration sources.
Sintering process: Optimize temperature curve (1200 ℃~1350 ℃) to reduce porosity<0.5%.
Electrode interface: Ni/Sn alloy electrode is used to buffer thermal stress and reduce interface defects.
3、 Industry testing standards and cases
1. International standards
IEC 60384-1: specifies the leakage current testing method and limits for MLCC.
Class I ceramics:<100nA (@ V_rated, 25 ℃).
Class II ceramics:<10 μ A (@ V_rated, 25 ℃).
AEC-Q200 (Automotive Electronics):
The leakage current needs to meet the requirement that the change after temperature cycling from -55 ℃ to+150 ℃ is less than 10%.
Example: A certain vehicle grade X7R capacitor has a leakage current of less than 5 μ A at 125 ℃.
2. Typical case analysis
Case 1: 5G base station filter
Select C0G medium (0402 package) with leakage current<5nA (@ 16V, 25 ℃) to ensure the purity of RF signals.
Failure risk: If the leakage current is greater than 10nA, it may cause an increase of 0.5dB in insertion loss.
Case 2: Electric Vehicle OBC Power Supply
Select X7R medium (1210 package), leakage current<2 μ A (@ 50V, 85 ℃), meeting high temperature reliability requirements.
Failure risk: If the leakage current is greater than 5 μ A, it may cause overheating protection of the power module.
4、 Selection suggestions and trends
1. Selection logic for leakage current control
Consumer electronics: Priority for Class I ceramics, leakage current<10nA, ensuring battery life.
Industrial control: Class II ceramics, leakage current<1 μ A, balancing cost and reliability.
Automotive Electronics: Class II ceramic with a leakage current of less than 5 μ A (85 ℃), certified by AEC-Q200.
Medical equipment: ultra-low leakage current design (<1nA), such as customized C0G dielectric+glass packaging.
2. The impact of emerging technologies on leakage current
Polymer capacitors: leakage current<0.1nA, but high cost, suitable for CPU core power supply.
Flexible MLCC: Using polyimide substrate, leakage current increases by<20%, meeting the bending requirements of wearable devices.
3D stacked MLCC: By reducing the number of dielectric layers through vertical interconnection, the leakage current is reduced by 30%, but the process complexity is high.
5、 Summary: Reasonable range and balance of leakage current
The leakage current range of MLCC needs to be comprehensively judged based on the application scenario:
Conservative interval:<10nA (Class I ceramics, high-precision scenarios).
General range: 0.1 μ A~1 μ A (Class II ceramics, industrial/automotive electronics).
Tolerance range: 1 μ A~10 μ A (Class II ceramics, low-cost consumer electronics).
When selecting, it is necessary to weigh the type of medium, voltage margin, temperature range, and cost, and verify long-term reliability through accelerated life testing (such as 85 ℃/85% RH/1000h). With the advancement of materials science and manufacturing technology, the leakage current of MLCC will continue to break through to sub nanometer level, providing support for high-frequency, high-temperature, and high reliability applications.