Highly customized,coils come in various specifications

A highly customized passive component, coils come in various specifications that include materials, size, configuration and winding structure.

Wire winding is the key manufacturing process. A typical model is made of wires wound in cycles on an insulating pipe, which can be air, steel, magnet or copper core. The two ends of the product are configured as electrodes for connecting on circuits. Round and rectangular are the most-popular forms.

There are various winding methods. During the design stage, suppliers select the process based on the coil’s function on the circuit. To illustrate, in creating air types, the parameters are the kind of circuit, inductance and diameter of the coil skeleton.

The interwound subcategory, for instance, can achieve good performance and stability when the number of cycles is less than five even without the last. Its Q value can reach 150 to 400. The variant is used in high- and super high frequency circuits. The single-layer subclass, meanwhile, fits short- and medium-wave circuits, and has a Q value between 150 and 250.

Magnet core materials are chosen based on the targeted frequencies. For coils operating in the audio range, silicon steel permalloy is adopted. Ferrite cores, which are made by winding multistrand insulated wires, are favored in low- and midlevel radio frequency variants for their elevated inductance. When the requirement is more than several megahertz, high-frequency ferrite or air cores with a single-strand thick silver-coated wire are utilized. For models of 100MHz or above, the latter is preferred.

The wires used are solid or hollow and can be insulated, enameled copper or cotton-enameled and covered. The diameter ranges from 0.15 to 4mm. These should meet the coil requirements on carrying capacity and mechanical strength. As such, thin wires are not suitable as they will increase resistance and reduce the Q value, and burn or break easily.

Enameled wires are the key material in coil production. These can be sourced locally but many companies favor those from Japan and Taiwan providers to attract overseas buyers. They also believe that imported inputs are better in consistency, copper content, surface coating and metallographic structure. Although the cost of enameled wires rose 20 percent in 1H10, makers are optimistic rates will stabilize for the rest of the year. Some suppliers are therefore keeping prices at current levels.