Why Capacitor Leads Should Be Kept Short In a Circuit

The leads of capacitors normally are very long when they are manufactured. The anode and the cathode leads can extend down for several inches on capacitors.

However, plugging a capacitor with the leads this long into a circuit can create some issues in the circuit.

When you have capacitors that have very long leads close to each other, these leads are, essentially, wires. When you have wires close to each other in circuits, they can produce an inductive effect. Even a small amount of wire has considerable inductance, which can resonate with a capacitor. When you have this, inductance serves to impede or block high-frequency signals. A capacitor which has low reactance at high frequencies may now impede high-frequency signals from passing through. This may be unintended and depending on the capacitor use for the circuit, the capacitor may fail to serve its intended role.

Therefore, capacitors lead must be kept short, less than 1.5mm in length, to effectively stop inductive effects, which can limit a capacitor's ability to pass high-frequency signals.

Surface mount capacitors are great to use because their very short leads being placed directly on the power plane of a circuits stops any inductance.