As a new PCB assembler, you might think that selecting a capacitor for your circuit is simply a matter of knowing its voltage and capacitance requirements. Newsflash: a lot more factors go into the decision. These include temperature, ESR, resonance, dissipation factor, and more. Leave out any of these important variables, and you might as well kiss your design goodbye.

If you choose one that doesn’t meet the necessary specs, your device could crash and burn faster than a dragster at the starting line. So, pay close attention as we reveal all the key factors for selecting the perfect capacitor for your PCB.

How to Identify the Right One for Your PCB Assembly


What is a PCB capacitor?

An indispensable component of modern technology, PCB capacitors are present in a wide range of electronic devices, from cell phones and computers to medical devices and audio equipment.

PCB capacitors play a critical role in regulating voltage and protecting signal transmission, preventing the build-up of electrical potential between components and providing a steady supply of power to the device.

Like a battery, capacitors are a type of passive component that stores electric charge for a brief period before releasing it back to the circuitry as needed. This helps maintain a stable current flow within the circuitry, ensuring smooth operation.

Different types of PCB capacitors have their own unique properties and applications in electronic design. The dielectric material or conductor used to make the capacitor can help with its identification.

What are the roles of PCB capacitors?

PCB capacitors are a crucial component in modern electronics, playing various roles in printed circuit boards.

Among these roles, coupling capacitors are essential for transferring signals between circuit stages while blocking DC signals. Decoupling capacitors act as a buffer, filtering voltage spikes and maintaining low dynamic impedance. Filtering capacitors are utilized to eliminate unwanted noise or interference in a circuit.

Additionally, capacitors are used to stabilize voltage levels and smooth out power supply ripples. Overall, PCB capacitors have a wide range of uses, making them an indispensable part of electronic design.

Types of PCB capacitors available

Typically, there are types of capacitors used in printed circuit boards (PCBs):

  • Aluminum electrolytic capacitors: these come in two types, etched foil, and plain foil. They have high capacitance values relative to their size due to the thickness of the aluminum oxide coating and the high breakdown voltage. They’re commonly used for coupling and DC blocking. But some assemblers prefer to use them as smoothing or flattening capacitors in power supplies.
  • Ceramic capacitors: these are some of the most common capacitors and come in two types, disc and multilayer ceramic capacitors (MLCC). They have high capacitance ratings and are great for filtering out high frequencies. They use dielectric materials with a much greater dielectric constant.
  • Tantalum capacitors: these are electrolytic capacitors with an anode made of tantalum metal and a cathode made of either liquid or solid electrolyte, and an oxide layer that serves as the dielectric. They have a higher capacitance per unit of size and are smaller than ceramic capacitors.
  • Film capacitors: these are non-polarized types of capacitors employed in various applications, made of insulating plastic film used as a dielectric. They are versatile and cost-effective.

Factors to consider when choosing a capacitor

PCB developers must consider various factors when choosing the right capacitor for their design. The most important ones are:

1. Dielectric Permittivity

Dielectric permittivity is a measure of a material’s ability to store electrical energy in an electric field. The higher the dielectric permittivity of a capacitor’s dielectric material, the higher its capacitance. Designers can calculate capacitance using the formula:


Where C is the capacitance, ε is the dielectric permittivity, A is the plate area in square meters, and d is the distance between the plates in meters. Different capacitor types have different dielectric materials, which affect their characteristics.

2. Temperature

Each capacitor has a maximum operating temperature, and exceeding it can cause the insulation around the dielectric to degrade, leading to electrolyte loss and leakage current. Assemblers should select capacitors that can operate safely under the maximum operating temperature of their application.

3. Effective Series Resistance

The equivalent circuit of a capacitor includes effective serial resistance (ESR) and effective serial inductance (ESL). The ESR value changes with frequency and temperature, and it is highest in electrolytic capacitors and lowest in film capacitors. PCB makers should choose capacitors with low ESR values, especially in high-frequency applications.

4. Resonance

As a signal travels through a capacitor, it experiences insertion loss, which reduces its power. The loss increases with frequency until the capacitor reaches its self-resonance frequency, where the impedance becomes zero. In high-frequency applications, a high self-resonance frequency (or low ESL value) is recommended for better noise suppression.

5. DC Biasing

The capacitance rating on a capacitor’s datasheet is under ideal conditions without any DC supply. However, in practical applications, a small DC supply can change the capacitance value of a ceramic capacitor with a high dielectric constant. Ideally, you should go for capacitance value capacitors, use larger package sizes, or switch to different types of capacitors to mitigate this issue.

6. Tolerance

The tolerance value represents the minimum and maximum range of a capacitor from its nominal value. For sensitive applications, engineers should choose capacitors with a low tolerance value. For coupling capacitors, capacitors with wide tolerance values are preferable.

7. Dissipation Factor

Capacitors have internal resistance, which causes power loss when an AC voltage is applied. The rate of loss is called the dissipation factor (DF). Different capacitors have different DF values at different stages of rated voltage, temperature, and frequency of operation. Engineers should select capacitors with the lowest DF possible for their application.

Choosing the best capacitor for your circuit board

To sum up, selecting the appropriate capacitor for your PCB design is crucial to ensure optimal circuit performance and reliability. As seen, different capacitors have unique features and characteristics that impact their suitability for specific applications.

Therefore, it’s essential to consider factors such as capacitance, voltage rating, temperature range, size, and cost when choosing a capacitor. Working with a reliable EMS PCB assembly partner can also help ensure you select the right capacitor and achieve the best results for your electronic product.