What are the materials of surface mount capacitors?

As one of the most fundamental components in electronic circuits, the material selection of surface mount capacitors (MLCC) directly affects the electrical performance, reliability, and cost of the device. The core materials of surface mount capacitors are systematically analyzed from three dimensions: ceramic dielectric system, electrode materials, and packaging materials, combined with technical characteristics and application scenarios
1、 Ceramic dielectric system: the core determining electrical performance
1. Class I ceramics (temperature compensation type)
Material properties:
Main components: Barium titanate (BaTiO) - based composite oxide.
Temperature coefficient: close to zero (C0G/NP0), capacity changes with temperature<± 30ppm/℃.
Loss tangent:<0.1%, excellent high-frequency characteristics.
Typical applications:
RF circuits (such as 5G base station filters)
Precision oscillation circuit (such as crystal oscillator load capacitor)
High Q-value filter (such as communication module)
2. Class II ceramics (high dielectric constant type)
Material properties:
Main components: Zirconium/Titanate based composite materials (such as X7R, X5R).
Dielectric constant: up to 3000~10000, with a unit volume capacity more than 10 times that of Class I ceramics.
Temperature coefficient: X7R (-55 ℃~+125 ℃, Δ C/C ₀=± 15%), X5R (-55 ℃~+85 ℃, Δ C/C ₀=± 15%).
Typical applications:
Power filtering (such as DC-DC module input/output terminals)
Energy storage capacitors (such as CPU core power supply)
Coupling/decoupling circuits (such as audio amplifiers)
3. Class III ceramics (semiconductor type)
Material properties:
Main components: Barium titanate with rare earth elements (such as Y5V, Z5U) added.
Dielectric constant:>10000, but poor capacity stability (Δ C/C ₀=± 22%~+82%).
Nonlinear characteristics: significant voltage coefficient (capacity decreases with increasing voltage).
Typical applications:
Low cost filtering (such as home control board)
Non critical energy storage (such as LED driver)
Attention: It has gradually been replaced by polymer capacitors.
2、 Electrode materials: affecting reliability and high-frequency characteristics
1. Metal electrode system
Silver palladium electrode (Ag/Pd):
Proportion: 70% Ag+30% Pd (early mainstream).
Advantages: Strong resistance to solder corrosion and high reliability.
Disadvantages: High cost, prone to "silver migration" (ion migration under high temperature and high humidity).
Application: Automotive grade capacitors (such as AEC-Q200 certified products).
Nickel electrode (Ni):
Advantages: Low cost, good sulfur resistance.
Disadvantage: The end needs to be sintered (to prevent oxidation), and the process is complex.
Application: Consumer electronics (such as mobile phones, tablets).
Copper electrode (Cu):
Advantages: Best conductivity (resistivity 1.7 μ Ω· cm), low cost.
Disadvantage: Easy to oxidize, requiring special packaging.
Application: High end server power supply (such as Intel VR13 platform).
2. Substrate material
Ceramic substrate:
Material: 96% alumina (Al ₂ O ∝) or aluminum nitride (AlN).
Characteristics: High thermal conductivity (AlN up to 170W/m · K), suitable for high-power applications.
Application: IGBT driver circuit, laser power supply.
Flexible substrate:
Material: Polyimide (PI) or Polyester (PET).
Features: Flexible and impact resistant.
Applications: Wearable devices (such as smartwatches), flexible electronics.
3、 Packaging material: key to protection and heat dissipation
1. End coating
Tin lead coating (Sn/Pb):
Proportion: 63% Sn/37% Pb (traditional process).
Advantages: High welding reliability and resistance to thermal fatigue.
Disadvantage: Environmental restrictions (RoHS ban).
Application: Military industry, aerospace (exempted fields).
Pure tin coating (Sn):
Advantages: RoHS compliant, low cost.
Disadvantage: Easy to grow tin whiskers (leading to short circuit risk).
Improvement plan: Add 1%~3% Ni to inhibit tin whisker growth.
Application: Consumer electronics, communication devices.
Silver plating (Ag):
Advantages: Best conductivity, low high-frequency loss.
Disadvantage: prone to sulfurization and blackening, requiring sealing and packaging.
Application: High frequency circuits (such as 5G base stations).
2. Shell material
Epoxy resin encapsulation:
Features: Low cost, simple process.
Disadvantage: High moisture absorption rate, prone to cracking at high temperatures.
Application: Universal capacitors (such as 0402/0603 packaging).
Ceramic packaging:
Features: Good airtightness and radiation resistance.
Disadvantages: High cost and large size.
Applications: Automotive electronics (such as ABS controllers), aerospace.
Metal encapsulation:
Features: Excellent heat dissipation performance and resistance to mechanical impact.
Disadvantages: Heavy weight and high cost.
Application: High power power supply (such as electric vehicle OBC).
4、 Emerging Materials and Technology Trends
1. Polymer capacitors
Material properties:
Medium: Conductive polymer (such as PEDOT: PSS).
Advantages: ESR as low as 1m Ω, excellent high-frequency characteristics.
Typical product: TDK CGA series (used for CPU core power supply).
2. Supercapacitors
Material properties:
Medium: Activated carbon+electrolyte.
Advantages: Capacity up to Farad level, fast charging and discharging speed.
Typical application: Backup power supply for IoT devices (such as NB IoT modules).
3. Flexible MLCC
Material properties:
Substrate: Polyimide (PI).
Advantages: Flexible radius<5mm, bending resistance>100000 times.
Typical application: Flexible electronics (such as foldable phones).
5、 Selection Decision Framework
High frequency/precision scenarios (such as 5G base stations, RF front-end):
Selection: Class I ceramic (C0G/NP0), silver plated end, ceramic packaging.
Key parameters: Temperature coefficient<± 30ppm/℃, ESR<10m Ω.
Large capacity/power filtering scenarios (such as DC-DC modules, LED drivers):
Selection: Class II ceramics (X7R/X5R), pure tin coating, epoxy resin encapsulation.
Key parameters: Capacity ≥ 10 μ F, withstand voltage ≥ 25V, ripple current>1A.
High reliability scenarios (such as automotive electronics, medical equipment):
Selection: Silver palladium electrode, ceramic packaging, AEC-Q200 certification.
Key parameters: Operating temperature -55 ℃~+125 ℃, sulfur resistance meets ASTM B809.
Emerging technology scenarios (such as wearable devices and the Internet of Things):
Selection: Flexible MLCC, polymer capacitor, ultra-low ESR.
Key parameters: bending radius<5mm, ESR<5m Ω, static current<1 μ A.
Through the above material system and selection framework, it is possible to accurately match the technical requirements and commercial demands of surface mount capacitors, achieving the optimal balance between circuit performance and cost. With the advancement of materials science, new ceramic media (such as strontium barium titanate BST), electrode materials (such as graphene), and packaging technologies (such as 3D stacking) will continue to drive technological innovation in surface mount capacitors.