Archive: Oct 2022

Electrical Coil Design: Thermal Challenges

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Electric coils conduct energy and allow for inductance to counter or control the flow of current. The coils are constructed from wires (made from conductive materials like copper) which may be wound around a cylinder, disk, or toroid-shaped ferromagnetic core or as a self-supported structure (wire only). While electric coils operate based on simple principles, manufacturers can design and construct electric coils with different capabilities for a wide range of consumer, commercial, and industrial applications. At Custom Coils, we specialize in producing coils for the following industries:

Electrical Coil Design

Manufacturers consider these four design elements to create custom electrical coils and overcome thermal challenges:


The basis of any electromagnet starts with a conductor wrapped in a defined shape/structure.  The shape, thickness, and length of the wire all factor into the coil’s magnetic field, the energy loss, and the ability of the coil to complete different functions. The resistance of the wire and the insulation required for the coil may dictate the type of wire used.

For electrical coils used in harsh or demanding environments, electroplated wires can withstand potential deterioration. Electroplating processes coat the wires with materials like gold, nickel, or silver, as well as an insulative coating.


Electrical coils also need insulation to isolate the windings as well as protect the wires from extreme heat and thermal damage. It sits between the wires so they don’t make contact and fail due to shortage. Manufacturers can help select the right type of insulation for an electrical coil based on the coil’s anticipated thermal capacity, the wire gauge, and the product’s applications.

Types of Coil Winding

Manufacturers wind wires around the ferromagnetic core in a precise shape and design to fulfill different functions. The type of coil winding in an electrical coil will be determined based on the:

  • Insulation
  • Quality
  • Inductance
  • Type of magnetic field being generated

Core Material

The coil’s core is an essential element. Different types of core materials produce magnetic fields of different strengths and affect the coil’s inductance.

Thermal Challenges

Cooling and Thermal Control

Often the dimensional constraints and operational requirements of the electromagnet produce a coil that will heat up beyond temperature limits of the materials or system it is operating in.

A coil’s magnetic field is directly driven by the number of turns on the coil and the amount of power input (amps).  Typically, the magnetic field requirements for the coil drive specific turn count and power requirements to generate the desired field; however, the coil dimensions constrain the number of turns that can be wound in the given dimensional space. This will require higher power input to the coil and may drive the temperature beyond the material or operational limits. Additional cooling may be required to draw heat out of the coil.

Cooling Applications:


Heat Sink: A structural holder (as defined above) can often act as a heat sink to draw heat away from the coil. For example, a coil wound in a copper bobbin (copper has a high thermal conductivity) will conduct heat out of the coil through the bobbin. Often times, heat sinking material is used, along with convection (fans, air flow) to provide enough cooling flow out of the coil.


Heat Sink with Cooling:  Similar to above, if heat sink with convection not enough to control temperature, a cooling path can be designed into a structural holder for the coil.


In-line Cooling: Hollow core conductors are used to wind the coil and act as the electrical path and the cooling path. This allows for cooling to run through the coil itself and they are typically used in high-power applications.


Copper Tube Cooling:  Depending on the size of the coil, copper tubing can be applied on the ID, OD, or in the center of the coil windings.

Temperature Sensor/Cut-off

 Thermal sensors can be applied to a coil to monitor temperature and control operation when a coil gets too hot or rises beyond operational limits.

Sensor Types

  • Thermocouples: Thermocouples can be applied externally on the coil or applied during winding at various internal points in the coil. Thermocouples monitor temperature and allow user flexibility in regard to actions taken when various temperature situations occur. They are typically integrated into the power supply system to monitor the coil temperature and determine whether to decrease power and/or shut down the system at various temperatures. 
  • On/Off Temperature Switch: These are on/off switches made to shut off power at a specified temperature. These can typically be applied externally on the coil and/or in line with the lead wire to the power source.

Custom Electrical Coils From Custom Coils

At Custom Coils, we specialize in creating high-performance electrical coils with sufficient cooling solutions for long-term operations. Contact us today to learn more about our capabilities or request a quote to start your order. 

What is High-Density Plasma Technology?

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High-density plasma domes have traditionally been used as decorative objects due to their unique lighting effects, but they are also an integral part of the semiconductor manufacturing industry. This blog will explain high-density plasma domes and their modern applications in further detail.

High-Density Plasma Domes

Also called a plasma globe, a plasma dome is a clear glass ball or container filled with a mixture of different noble gasses and a high-voltage electrode at the center. Plasma forms within the container when you apply voltage. Consequently, plasma filaments extend from the central electrode to the inner walls of the glass insulator. The result is the appearance of several beams of colored light.

Different variations of high-density plasma domes exist. The most common variation is a clear glass sphere filled with gas mixtures at close to atmospheric pressure. These gas mixtures may include neon, krypton, xenon, and argon. 

The globes run on high-frequency alternating current. In most cases, the driving circuit is a type of power inverter, where a lower-voltage direct current supplements the inverter’s output with the help of a high-voltage, high-frequency transformer.

Applications of High-Density Plasma Domes

A high-density plasma dome is a single unit made up of several components, including:

  • A ceramic bell jar
  • A cooling/RF coil
  • Ground tabs/slugs
  • Machine parts
  • A non-conductive elastomer 

In semiconductor applications, high-density plasma chemical vapor deposition (HDP-CVD) is a technique that creates the crucial layers of insulation that separate and protect the electrical components. High-density plasma domes can be categorized based on the type of gasses they contain and their applications, which typically include RF assemblies and silicon wafers.

In addition to decorative and recreational purposes, high-density plasma globes can be part of an institution’s lab equipment for demonstration purposes. In particular, high-density microwave plasma machines can produce ions and free radical species. In these applications, the machine is made of a plasma source, the circuit, and the applicator.

High-density plasma domes can also be used in silicon wafer and RF assembly applications, where they are susceptible to damage with regular use. That’s why it’s important to partner with a reputable refurbishment and repair company.

When using high-density plasma domes, exercise caution especially in the following conditions:

  • Avoid bringing flammable items near the globes.
  • The domes may emit certain frequencies that interfere with phone and Wi-Fi signals. Therefore, keep them away from such areas.
  • Since they radiate electromagnetic waves, avoid operating the domes near people with pacemakers.

Custom Coils Capabilities

If you’re looking for high-density plasma dome repairs and refurbishments, Custom Coils is here to help. With over 30 years of experience, we are experts at developing high-quality, repeatable production processes for high-density plasma domes. We have shipped over 10,000 high-density bell jar parts, and we remain ready to take on any repair or refurbishment project, no matter how challenging or complex. What sets us apart from other suppliers is that we understand how critical parameters relate to material makeup.

Contact us to learn more about our capabilities, or request a quote to begin your project.