All about Micro-Coil Winding Process

The coil winding process is the heart of the manufacturing process of an electromagnetic coil where an electrical conductor is wound in the shape of a spiral, helix, or coil. Depending on the specific purpose of use, the manufacturers of the micro-coils design the shape and dimensions of a coil. The requirements of the customers for the strength of the desired magnetic field, inductance, and resistance are the significant factors that determine the design of the coil winding.

Electromagnetic coils have significant applications in several devices such as electromagnets, inductors, sensors, and transformers where interaction occurs between electric currents and magnetic fields. Electromagnetic coils follow the mechanism that either using an electric current through the wire, manufacturers generate a magnetic field or using an external magnetic field through the interiors of the coil, manufacturers generate an electric current in the conductor.

Challenges for Micro-coils:

The major challenge that the designers of invasive medical devices face is to fit the devices’ physical size within several constraints. Therefore, nowadays, in order to place the micro-coils within the devices, the size of the micro-coils has to be very tiny. Therefore, the manufacturing companies should have special equipment and built in-house machinery that is able to handle several factors such as-
i) To provide tight winding spaces,
ii) To offer a high-speed order fulfillment facility,
iii) Handling wires that are not straight, and
iv) The machines should be able to conduct the insulation process and avoid breaking points of the wire.

Methods and Machines for Coil Winding:

It is quite impossible to wind a coil by hand, especially when a huge number of micro-coils are to be manufactured. In order to conduct mass production of electromagnetic coils, it is essential to have automated machinery. Traditional methods for winding coils are not suitable and inefficient to fulfill industrial purposes. In terms of geometry and type of the wound coils, micro-coils can be classified into several categories such as helical, wild or jumble, and orthocyclic.

Winding coils in a helix involve the creation of layers by switching directions through moving forward and backward. However, this process requires fine wires because after reaching certain layers, the structure becomes so tight that it could not contain the layers.

For winding a micro-coil, the orthocyclic winding process is the most optimal method where the upper layer of wires takes place in the grooves of the lower layer of wires. By reducing the space and materials of the winding process, manufacturers can enhance the efficiency of the coil winding process. An efficient coil is capable of providing good heat conduction and distributed electromagnetic field strength across the windings.

Micro-Coil Winding:

In order to prepare serially wound micro-coils, we can not use the equipment that is used for winding regular-sized coils. The manufacturing of micro-coils needs the development of in-house and specialized equipment, and the manufacturing company should possess state-of-the-art methods.

Although the production of micro-coils involves about 2000 turns of the wire, due to the miniaturized size of the coil, the thickness of the wire should be reduced. The thinnest ultra-fine copper wire has a diameter of 9 microns. Therefore, using this ultra-fine wire, to manufacture over 1000 windings which is smaller in comparison to the head of a pin, manufacturers require custom micro-machining technologies. Due to the tiny diameter of the ultra-fine wires, one can not use the traditional soldering or welding methods, because these methods can cause the destruction of the wires. Therefore, in order to overcome the drawbacks of these methods and to provide effective soldering for the wires to meet tight tolerances at very high temperatures, modern manufacturers use thermo-compression bonding technology.

Applications:

As the demand for miniaturized devices is increasing, the application area of micro-coils is expanding. Micro-coils are essential for several applications such as-

• In order to control and monitor miniature implants and transfer logging data to/from the implants,
• In order to activate and operate their systems, miniature implants require electrical charge input or battery charging, and the micro-coils help to transfer that energy,
• In several treatments such as heat treatments, RF or radiofrequency treatments, electromagnetic pulse and electromagnetic radiation-based treatments,
• To conduct in-vivo magnetic navigation where an external or a local magnetic field is required.

Thus, for this extensive area of applications, there are limitless possibilities for micro-coil winding technologies.