Coil Winding Technology: Materials for Micro Coils

Coil winding technology using ultra-fine wires is essential for the manufacturing of inductive components and providing connectivity within tiny medical devices. This technology involves several methods and is effective to handle copper and other conductive metal wires of any diameter. With this technology, modern-day manufacturers can even connect ultra-fine wires of 9 microns in diameter that is 5 to 12 times thinner compared to human hair.

Depending on the application area, parameters for micro-coil can be different. Similarly, depending on the requirements of the customers, manufacturers can choose different materials for the manufacturing of micro-coil. The most common materials for the preparation of micro-coils are copper, aluminum, stainless steel, titanium, and precious metals with high purity such as gold, platinum, etc. However, in order to ensure the excellence of the micro-coil manufacturing process, careful consideration is essential for meal selection.

Materials and Their Characteristics:

1. i) Copper:

In terms of conductivity, copper takes second place after silver. Therefore, due to its excellent conductivity and other physical properties, copper has a huge application in the medical industry. Copper is also an exceptionally durable and reliable material. Copper alloys have also gained huge popularity or several applications. To protect the copper wire, manufacturers use some sort of coating (enameled wire). Nevertheless, the type of coating depends significantly on the application area.

1. ii) Stainless Steel:

Stainless steel offers several significant characteristics such as corrosion and heat resistance, durability and fully recyclability, strong yet lightweight, etc. In order to serve heating purposes, stainless coils are useful. For instance, in the case of cryotherapy treatment where defrosting is essential between different freezings for cancer tumors, stainless coils are useful. In potentially corrosive environments, stainless steel coils are most effective.

iii) Aluminum:

In the case of portable medical apparatus where a large number of turns can result in the heavyweight of the coil, aluminum metal is useful to lessen the weight. However, due to the high cost of coating and manufacturing processes, aluminum coils are very expensive. For this reason, manufacturers use aluminum coils rarely.

1. iv) Precious Metals with High Purity:

Precious metals such as gold and platinum are extremely chemically resistant and highly conductive. In the case of medical treatment when the coils are required to place in direct contact with tissue/ skin, these coils are effective. These coils are also useful to make the medical devices biocompatible following the FDA regulations. The applications of these coils are very rare due to the extremely high cost. However, in some critical situations, for instance, to reduce resistance, golden and platinum threads are very useful.

1. v) Titanium and Titanium Alloys:

Due to their remarkable corrosion resistance ability, titanium coils have significant applications in the medical field. In comparison to other ferromagnetic materials, these materials are effective for their non-magnetic properties. Titanium coils are suitable for many dental and medical applications due to their higher metal strength-to-weight ratios and lightweight.

Challenges and Solution for Coil Winding Technology:

Due to the tiny diameter of the ultra-fine wire, manufacturers face non-trivial challenges, especially when there are several physical and environmental factors upon the final shape of the micro-coils. Micro-coils also need to meet strict tolerance requirements. Therefore, during the winding process, innovative and custom-made machinery is required in order to monitor and control the position and tension of the wires. 

However, manufacturing challenges are not the only complexities to use micro-coils for medical applications. As these coils take part in the larger systems, there are some additional challenges regarding their electrical connections with the systems. In order to overcome such challenges, traditional soldering-based connections are ineffective. The traditional heat-based soldering method for ultra-fine wires causes several unexpected side effects. For instance, oxidization and vicinity of the connection can result in low durability and inferior connectivity; excess strain can cause degraded durability; heat damage of a specific area can result in degraded connection durability and reliability.

The ultimate solution for these connectivity challenges is thermo-pressure bonding technology. This technology is very much effective to connect ultra-fine wires of similar or different diameters. The molecular connections of the thermo-pressure bonding technology help to provide corrosion-free, strain-free, and highly reliable and durable connectivity without using the soldering method. Therefore, this technology is also effective to lessen the manufacturing cost.