There are many types of SMD capacitors, which can be classified in various ways. The following are several main classification perspectives and their common types:
1、 Classification by medium material (the most core and commonly used classification method)
Ceramic Chip Capacitor (MLCC)
Absolute mainstream: This is the most widely used and largest quantity of surface mount capacitors.
Structure: Composed of multiple layers of ceramic media and internal electrodes alternately stacked and sintered.
Characteristics:
Small size, wide capacity range (from pF level to hundreds of μ F level).
No polarity.
The price is relatively low.
Good high-frequency characteristics (especially suitable for high-frequency filtering and bypass).
High reliability.
Key subcategories (based on ceramic medium characteristics):
Class 1 (ceramic): high stability, low loss.
Typical representative: C0G/NP0- Excellent temperature characteristics (close to zero temperature drift), low dielectric constant, small capacity (usually ≤ 100nF), small loss tangent value, high accuracy (up to ± 5%). Suitable for high stability applications such as resonant circuits, oscillators, and high-frequency filters.
Class 2 (Class 2 ceramics): High dielectric constant, large capacity, but relatively poor temperature stability, voltage stability, and losses compared to Class 1.
Typical representative:
X7R: Wide operating temperature range (-55 ° C~+125 ° C), capacity change rate ± 15%. The strongest universality, widely used in power filtering, bypass, coupling, etc.
X5R: Operating temperature range (-55 ° C~+85 ° C), capacity change rate ± 15%. The cost is slightly lower than X7R.
Y5V has the highest dielectric constant and the largest capacity per unit volume, but its temperature characteristics (-30 ° C~+85 ° C, capacity change rate can reach+22%/-82%) and voltage characteristics are poor, resulting in high losses. Suitable for situations with high capacity requirements but not strict stability requirements (such as low-frequency coupling, energy storage).
Other: Z5U, Z5V, etc., with characteristics similar to Y5V but worse, are now less commonly used.
Tantalum SMD Capacitor
Characteristics:
Large capacity per unit volume (usually larger than MLCC at the same volume).
The equivalent series resistance (ESR) is relatively low and stable, especially for polymer tantalum.
Has good filtering performance.
Has polarity.
Key subcategories (by cathode material):
Manganese dioxide tantalum capacitors: traditional mainstream. The price is relatively low, but there is a risk of "failure, short circuit, and combustion" (strict derating is required, usually 50% of the rated voltage), and the ESR is relatively high compared to polymer tantalum.
Polymer tantalum capacitor: The cathode material is a conductive polymer.
Advantages: Extremely low ESR (much lower than tantalum manganese dioxide), strong ability to withstand surge currents, and failure modes mostly open circuit (safer).
Disadvantages: High price, relatively large leakage current (but within an acceptable range).
Application: Mainly used for power filtering and decoupling applications that require large capacity and low ESR (especially when space is limited), such as CPU/GPU power supply and DC-DC converter input/output filtering.
SMD Aluminum Electrolytic Capacitor
Characteristics:
The capacity can be made very large (from μ F level to mF level).
Low cost (especially when dealing with large capacity).
Has polarity.
Relatively large in volume (especially compared to MLCC of the same capacity).
The equivalent series resistance (ESR) is relatively high.
The lifespan is greatly affected by temperature (the electrolyte will dry up), and the lifespan is relatively short.
Good low-frequency characteristics, poor high-frequency characteristics (not suitable for high-frequency filtering).
Application: Mainly used for low-frequency power filtering, energy storage, and input/output high-capacity filtering (such as power adapter output terminals), it still has advantages in situations where space requirements are not high and ultra large capacity is needed. There are plug-in and patch packaging options available.
SMD Film Capacitor
Characteristics:
Good stability (temperature, frequency, voltage), high accuracy.
The tangent value of the loss angle is small (low loss).
No polarity.
High insulation resistance.
The capacity range is usually from pF to μ F (generally less than 10 μ F).
The price is relatively high and the volume is relatively large.
Key subcategories (by dielectric film material):
Polyester film (PET, Mylar): Low cost, good capacity to volume ratio, but average temperature stability and high-frequency loss characteristics.
Polypropylene film (PP): excellent performance, extremely low loss, good temperature stability, and good frequency characteristics (self-healing). Commonly used in high demand scenarios such as audio coupling, high-frequency pulses, resonance, filtering, timing, EMI suppression.
Polyphenylene sulfide film (PPS): It has good high temperature resistance, good temperature stability, and frequency characteristics between PET and PP.
Application: Circuits that require high stability, accuracy, and low loss, such as precision analog circuits, timing circuits, resonant circuits, audio circuits, A/D converters, sample and hold circuits, high-frequency power circuits (PP), safety capacitors (X2/Y2), etc.
SMD Supercapacitors/EDLCs
Characteristics:
The capacity is extremely large (up to Farad level), between traditional capacitors and batteries.
High power density and fast charging and discharging speed.
Long cycle life (hundreds of thousands of cycles).
The working voltage is low (usually 2.5V-3.8V per unit).
There is leakage current.
Application: Mainly used in situations that require short-term high-power pulses or backup power, such as RAM data retention, real-time clock (RTC) backup power, energy harvesting and storage, IoT devices, motor start-up assistance, etc.
2、 Classified by packaging size
The packaging size of surface mount capacitors has international standards (EIA standards), which are represented by four digits (in English units, the unit is one percent of an inch). Common sizes include:
0201 (0603 metric): 0.6mm x 0.3mm - Ultra small, commonly used for high-density boards.
0402 (1005 metric): 1.0mm x 0.5mm - Small, commonly used for high-density boards.
0603 (1608 metric): 1.6mm x 0.8mm - Very common.
0805 (2012 metric): 2.0mm x 1.25mm - Very common.
1206 (3216 metric): 3.2mm x 1.6mm - Common.
1210 (3225 metric)： 3.2mm x 2.5mm
1812 (4532 metric)： 4.5mm x 3.2mm
1825 (4564 metric): 4.5mm x 6.4mm - typically used for large capacity MLCC or tantalum capacitors.
2220 (5750 metric): 5.7mm x 5.0mm - typically used for aluminum electrolysis or large capacity MLCC.
2225 (5764 metric)： 5.7mm x 6.4mm
Larger sizes, such as 3528, 7343, etc., are mainly used for aluminum electrolysis or supercapacitors.
3、 Classified by temperature characteristics (mainly for MLCC)
C0G/NP0: The temperature characteristics are the most excellent (almost zero change).
X7R: Good temperature characteristics (± 15% variation).
X5R: Temperature characteristics are generally (± 15% variation).
Y5V: Poor temperature characteristics (+22%/-82% variation).
4、 Classified by accuracy (allowable deviation of capacity)
Common accuracy levels: B (± 0.1pF), C (± 0.25pF), D (± 0.5pF), F (± 1%), G (± 2%), J (± 5%), K (± 10%), M (± 20%), Z (+80%/-20%), etc. C0G/NP0 can usually achieve high precision (such as G/J/K), while X7R/X5R/Y5V is usually K/M/Z, etc.
5、 Classified by rated voltage
The maximum DC voltage that a capacitor can operate stably for a long time. Common series include: 6.3V, 10V, 16V, 25V, 50V, 100V, 200V, 500V, 630V, 1kV, 2kV, 3kV, etc. When making a choice, sufficient design margin should be considered (for reduced usage).
Summary and selection suggestions
Preferred MLCC: For the vast majority of general scenarios (bypass, decoupling, coupling, small capacity filtering), MLCC is preferred. Choose C0G/NP0, X7R or X5R according to temperature stability and capacity requirements. Avoid using Y5V in critical positions.
Requires a larger capacity:
If space permits and high frequency characteristics are not required, aluminum electrolysis (low-cost) can be considered.
If space is limited and low ESR is required, polymer tantalum capacitors (with good performance and safety) are preferred, followed by manganese dioxide tantalum capacitors (requiring strict derating).
If the capacity requirement is extremely high (Farad level), consider supercapacitors.
High demand scenarios: require extremely high stability, accuracy, and low loss (such as precision simulation, timing, resonance, audio, high-frequency power), considering thin film capacitors (especially PP).
Package size: Choose according to PCB space and assembly process capability. High density design tends towards 0201/0402/0603.
Voltage margin: It is necessary to ensure that the operating voltage is lower than the rated voltage and leave sufficient margin (such as 50% -80% of the rated voltage, depending on the capacitor type and application).
Polarity Attention: Tantalum capacitors and aluminum electrolytic capacitors have polarity. When welding and circuit design, attention must be paid to the direction. Reverse connection can cause short circuit failure or even explosion (tantalum capacitors are particularly dangerous).
Understanding these classifications and their characteristics is key to correctly selecting and using surface mount capacitors in electronic circuit design.