Capacitors are an essential component of modern circuitry and are present in nearly every electrical device. These passive components are found in fundamental electronic subsystems such as RC circuits (resistor/capacitor), RLC circuits (resistor/inductor/capacitor), power circuitry, power supply units, and much more.
The three most common types of capacitors are ceramic, thin film, and electrolytic capacitors, given their versatility, cost-effectiveness, and reliability. This article examines how these three types of capacitors are manufactured and highlights some key differences.
What are capacitors made of?
At a fundamental level, capacitors are made of two electrodes (conductors, often metal) separated by a dielectric (insulator). When an electrical signal is applied to one of the electrodes, energy is stored in the electrical field between the two separated electrodes. The stored amount of energy is called ‘capacitance.’ When designing a capacitor, the capacitance can be controlled by three critical characteristics:
The size of the electrode plates. The larger the surface area of the electrodes, the more energy can be stored within that area, therefore increasing capacitance.
The proximity of the plates to each other. When two electrodes are relatively far apart, their ability to create an electric field (via induction) is reduced. As the two electrodes get closer to each other, the ability to form an electrical field increases, and the capacitance can be much larger.
The insulation material between the electrodes. Various dielectric materials can increase capacitance by reducing the electric field between the electrodes, allowing more charge to be stored on the electrodes at the same voltage.
Given these three fundamental capacitor variables, many manufacturing techniques are commonly used to create capacitors of varying capacitance, voltage capacity, temperature thresholds, reliability, cost, safety, size, and dissipation loss.
Learn more about the use of dielectrics in capacitors.
How electrolytic capacitors are made
Aluminum electrolytic capacitors are famous for their low cost and ability to hold large amounts of energy in a small package compared to ceramic or film capacitors. While electrolytic capacitors are very popular, they are more sensitive to unwanted voltages and temperature than other capacitors and have relatively high current leakage.
The aluminum electrolytic capacitor manufacturing process begins by etching thin aluminum foil via a chemical bathing process. This etching process forms a thin layer of aluminum oxide on the anode. This oxidized layer acts as the dielectric layer between the anode and cathode, which is another layer of thin aluminum foil.
The anodized aluminum foil anode is then spooled together with the aluminum cathode foil, separated by a thin layer of paper. Terminals are connected to the anode and cathode layers at the terminal ‘deck’ that is eventually used to connect to external circuitry.
The foil-paper-foil winding is then placed in the external housing of the capacitor unit, often called a ‘can.’ Next, an electrolyte solution is wicked through the winding via the paper layer. The capacitor can is then sealed with the deck and is thermally aged to repair any dielectric faults and monitor electric properties. Once aged and tested, the capacitor is ready for use.
View our guide for help on how to select the right aluminum electrolytic capacitor.
How ceramic capacitors are made
Ceramic capacitors (commonly called MLCCs) are the most common capacitors in modern electronics. These capacitors use a ceramic material as the insulating dielectric between the anode and cathode plates. Ceramic powder, such as barium titanate, is mixed with a binding material to form a slurry. This slurry is then thinly applied to a thin metal sheet. Alternatively, metallic paste can be applied to the ceramic slurry.
The ceramic and metal layers are then stacked together, mechanically pressed at high temperatures, and cut into small discs or rectangles to form capacitor ‘chips.’ The external dimensions of the chips, as well as the layer distances, drive the capacitance values of the capacitor.
These chips are fired in a kiln at high temperatures to remove the binder, leaving only the ceramic and metal materials in the chips. The firing process can reduce the size of the unfired chips by 30% or more, depending on the materials used in the manufacturing process.
Once fired, the chips are sintered with termination ends that connect alternating layers of the electrodes to each terminal. These terminals are electroplated to provide a suitable surface for end-use soldering and placement on a PCB. After electroplating, the capacitors are ready for testing a capacitance verification.
Learn more about how ceramic capacitors work and what they do.
How film capacitors are made
Film capacitors tend to be more expensive than ceramic capacitors but have a much longer service life and a propensity for high-voltage applications. Additionally, film capacitors have much higher maximum operating temperatures than ceramic and electrolytic capacitors, making them suitable for many industrial and commercial environments.
Film capacitors utilize a plastic film layer such as polyester, polypropylene, or poly-impregnated paper as the dielectric insulator between the capacitor’s electrodes. The film is combined with metal by either vapor metallization or layering on a very thin metal sheet.
The metalized film is then ‘slitted’ and wound. The slitted film is accurately measured by length and width to ensure the required capacitance. These wound rolls are then combined in a co-winding process to form the two independent electrode layers.
Once wound, these windings are compressed and temperature treated to form a solid structure. The windings are masked and encapsulated to be electrically isolated from the surroundings, and leads are attached. The encapsulated capacitor winding is then inserted into a plastic structure and potted with resin to ensure longevity and protection from elements. Once potted, these capacitors are completed and ready for quality testing and testing.
Manufacturing different types of capacitors
As is true with all electronics sectors, a device's cost and functionality are driven by the materials used, the manufacturing process utilized, and the device's capabilities. These different processes allow for different capacitor types that achieve varying characteristics. The best type of capacitor depends on the application.
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