Surface Mount Inductors – Theory

Request_a_quote_btnViewTheoryPages_btnSurface mount inductors (and LINK: surface mount transformers) can be classified in several ways: by power rating, by type of application, by type of construction, by industry, and others. “Surface mount inductors” refer to a type of construction that permits attachment of surface mount inductors to a printed circuit board (PCB). Historically, inductors and other circuit devices have been mounted on PCBs using “pin-thru” technology. Inductor wires are terminated to pin type terminals. Holes are drilled in the PCB’s copper circuitry to accommodate the transformer pins. The inductor pins are inserted through these holes and then soldered to the copper circuitry. Engineers have developed solder pastes, adhesives, and assembly processes that permit attaching inductor terminals to PCBs without using holes. Flat areas (known as pads) on the inductor terminals are soldered directly to copper circuitry surfaces hence the term surface mount inductor (or transformer). This process eliminates the need to drill holes for the pins, thereby reducing the cost to manufacture a PCB.

Surface mount inductors (and transformers) are usually wound on surface mount bobbins, but are also available as toroidal coils. The toroidal coil is mounted on a “header” equipped with surface mount terminals. The bobbins (or headers), used with surface mount inductors, come in a variety of materials: plastics, phenolic, glass, Teflon and others. Most of these are molded. Some are fabricated. Some bobbins and headers are “self leading”. The winding wire is also used to form the surface mount terminal by looping the wire under a pre-formed flat edge thereby forming a reasonably flat terminal area.

Surface mount inductors (and transformers) are available in a variety of shapes. Surface mount inductor shapes include pot cores (round), “RM” (square pot cores), “EP”, “E”, “EI”, “EEM”, “EFD”, “U”, “UI”, “ER”, and some others including custom shapes. Surface mount inductors in these shapes are usually only available in the smaller sizes. Designers are adapting more shapes and larger sizes to surface mount inductor applications. Designers have mechanical concerns about the larger sizes. The weight of the larger sizes may exceed the weight that soldered surface mount pads can safely handle under vibration. Over time, designers hope to develop surface mount inductors (and transformers) in larger sizes.

Like other inductors, surface mount inductors (and transformers) can use a variety of core materials: laminated or taped wound silicon steel alloys, nickel-iron alloys, cobalt alloys; powdered irons and nickels; ferrite; air core; and/or core materials processed for square loop or round loop properties; and others.

Butler Winding can make (and has made) surface mount inductors (and transformers) in a wide variety of materials and sizes. Butler Winding can also do a variety of custom applications. Butler Winding’s upper limits are 40 pounds of weight and 2 kilowatts of power. We have experience with foil windings, litz wire windings, and perfect layering. For toroids, we can (and have done) sector winding, progressive winding, bank winding, and progressive bank winding. Butler winding has a variety of winding machines, bobbin/tube and toroid. That includes two programmable automated machines and a taping machine for toroids. Butler Winding has vacuum chamber(s) for vacuum impregnation and can also encapsulate. To ensure quality, Butler Winding purchased two programmable automated testing machines. Most of our production is 100% tested on these machines.