Capacitor technology serves a variety of functions in circuitry projects, from basic to complex applications. Two main parameters define a capacitor's type―form factor and dielectric material. Let's explore the difference between SMD capacitors and electrolytic capacitors, one of which is form-factor driven while the other is dielectric-distinguished.
Capacitor Form Factor
Aside from its capacitance, a capacitor's form factor is its most important characteristic. The two most common capacitor form factors across the electronics industry are:
· Surface Mount Device (SMD)
· Through-hole
SMD capacitors sit on top of a printed circuit board and are surface soldered to designated pads. By contrast, through-hole capacitors have long leads that are designed to pass through holes on a printed circuit board (PCB) and soldered accordingly. Through-hole capacitors are more common for prototyping circuits, while SMD capacitors are often used in mass production circuit design. These are the two most versatile form factors, but you can find other form factors available, such as:
· Screw terminal
· Hood
· Snap-in
· Press-fit
· Axial
Dielectric Type
A capacitor electrostatically stores energy by using a non-conducting dielectric to separate a cathode and an anode. Just as wooden gears perform differently than metal alloy gears, a dielectric's material properties impact the capacitor's:
· Capacitance
· Size
· Cost
· Breakdown voltage
Electrolytic capacitors use an oxide layer formed on the capacitor's anode as their dielectric. In concept, this method is similar to how rust forms on an iron plate. The thin dielectric layer allows for high capacitance values in a relatively small package. However, the capacitor must be polarized to perform correctly, which is why electrolytic capacitor polarity is often distinctively marked on the body. Electrolytic capacitors are well known for their high capacitance values and can be identified by their cylindrical shape. Other dielectric materials include mica, paper, film, and ceramic, all of which present varying characteristics and advantages in different applications.
SMD Capacitor vs. Electrolytic Capacitor
SMD capacitors can use electrolytic construction, though not all do. Many electrolytic capacitors have an SMD form factor, but not all.
For example, Kemet's ESH336M050AE3AA is a through-hole aluminum electrolytic capacitor with a 33uF capacitance and 50V compatibility. The EEV336M050S9HAA boasts the same performance, but is intended for surface mounting instead. By design, both capacitors are electrolytic capacitors that use an oxide-layer dielectric, but only the second model can be considered an SMD capacitor.
Given their higher capacitance values and voltage compatibilities, electrolytic capacitors are generally considered through-hole capacitors. However, even if you have limited board space that seemingly requires a small SMD capacitor, you may be able to find an electrolytic capacitor that can do the job.
