High Speed Low Loss Dielectric Extrusion

Breakthrough in Dielectric Technology

Another breakthrough in dielectric technology that we are still benefitting from today happened in the 1953 when Bell Lab’s and Mr. F.B. Lloyd at the Western Electric Company in the US to develop coaxial transmission line foaming and introducing air to extruded polyethylene and thereby lowering the capacitance and insertion loss.

Mr. F.B Lloyds R&D was established on a British patent, issued in the 1930’s. However it took many years and engineering staff to perfect the dielectric technology and as a matter of fact even to this day LOROM is spending huge amount of R&D resource to constantly be at the forefront of increasing bandwidth capabilities in dielectric technologies enabling the modern world need for increase data transmission speed. 

DuPont Airquick Polymer Technology

LOROM is proud to work with a multiple numbers of leading edge compound manufacturers of which one is DuPont®.

The DuPont® Airquick polymer foam technology comprises nucleating agents and base polymers that improves both the processing and end-use performance.

This new Teflon® fluoropolymer foam resins offers a broad range of wire and cable applications for data communications in multiple applications such as Data Centers, LAN networks, Military and commercial aircrafts.

LOROM offers a wide variety of DuPont® foams offering, high velocity of propagation dielectrics used in low loss plenum coaxial cables, differential pair cable constructions for data centers, medical cable as well as with low loss and small size (MCX series) with small uniform cell structure and good adhesion to the conductor resulting in excellent SI performance.

Benefits of Physical Foam

Physical foam is a more complicated process, but is has benefits that can out way the more complex process necessary to produce product. Physical foam requires a high-pressure gas injection system that is needed to be introducing gas into the melt stream at the gas’s critical velocity that will maximize absorption.

The foam or void content can be increased to 60% depending on materials but typically lower dielectric constants can be obtained with lower dissipation factors then those formed by chemically foamed process.

LOROM utilizes both methods in our manufacturing operations but for all of our mission critical product performance requirements we use Skin/Foam/Skin to enhance the mechanical stability of the foam structure.

Skin-Foam-Skin Dielectric technology

Modern communication technologies, whether its data centers or broad band GSM applications, it’s all about creating low insertion loss at reasonable economic product values.

Physical foaming provides exactly the solution to the above challenge, lower insertion loss cables with high value.

In addition, this extrusion technology ensures optimal mechanical performance due to the triple layer Skin-Foam-Skin construction that reduces, if not eliminates all of negative effects of the change of transmission line geometries do to crushing, flexing and or downstream processing in the wire plant itself.

Triple Layer Dielectric Technology

As the transmission speed and the data capacity has increased exponentially in recent years, the operating frequency cable components has equally shifted upward exponentially to higher frequency regions.

Differential transmission lines with lower insertion loss, constant tanδ (Dielectric loss tangent) and low dielectric constant and at the same time economically attractive products have been in high demand.

LOROM’s answer is an in-house developed polyethylene base material enabling “micro” foam structures evenly dispersed throughout the dielectric structure with a minimal addition of nucleating agents.

The Skin-Foam-Skin Nitrogen gas injected dielectric technologies developed by LOROM along with the associated downstream manufacturing equipment and process provides a solution to this well-known and defined problem.

Many of the cable companies in the world of high-speed cables are using solid dielectrics. The manufacturing process and process control for manufacturing Skin-Foam-Skin are extremely challenging and standard off the shelf equipment is nonexistent.

LOROM has a competitive advantage because the R&D and our ability to build cable machinery is an integral part of LOROMs manufacturing footprint and capability.

Cell Nucleation the Heart of Successful Foaming

Control of cell nucleation is crucial to obtaining the desired fine and uniform cell structure in the final foam structure. It is a complex area with several, often interrelated factors playing a role.

The main factors which influence cell nucleation:

• Higher rates of pressure drop at the die significantly increases the cell density, irrespective of the concentration of blowing agent gas and or external nucleator.
• High shear rates also play a role in promoting cell nucleation.
• It has also been established that higher concentrations of blowing agent and gas lead to increased cell density.
• The addition of external nucleating agents is the most commonly method used to control cell nucleation in the foaming process. Nucleating agents are basically defined as finely divided and dispersed solid particles, which provide sites for cell nucleation.

In line FFT measurement for closed loop control and for insuring consistency of all vital parameters necessary to produce products with excellent signal integrity performance.

Gas Injected Foamed Teflon

High Speed Low Loss Dielectric Fluoropolymer Foam is created by precisely controlled extrusion equipment that starts with DC drives and precision tuned temperature controllers.

The gas injection process is a high pressure metering system used in conjunction with a multiple stage screw design that mixes the gas in the correct proportions with the base polymer at the correct melt temperature.

Every aspect of LOROM’s extrusion process needs to be controlled so that when done correctly it forms a high performing dielectric. This means that the resulting foam has a uniform structure which delivers low loss and superior performance.

This physical foaming process can produce a finely dispersed cell structure that still needs to be controlled by LOROM’s closed loop system.

LOROM extrusion system can predict and control all aspects of creating a high performance dielectric in real-time, with capacitance, diameter and concentricity gauges that interface with control loops that regulate line speed and quench position.

By introducing gas injected voids into FEP or PFA polymeric insulation material the dielectric can be significantly improved. LOROM’s capability to control the size and distribution of “bubbles” throughout the dielectric avoids any significant degradation of the dielectric performance.

Foaming Dielectrics Significance

Foaming dielectrics offers significant advantages over conventional melt extrusion technologies such as:

• Low Dielectric Constant
• Reduced weight and Size
• Reduced Loss or Attenuation
• Increased Velocity of Propagation
• Low Capacitance and Higher Impedance at reduced dimensions

Chemical and Physical Foaming of Plastic Materials

Foaming of plastic materials for wire and cable applications are typically done by two methods, chemically and physically. Let’s first talk about the features and benefits of both.

Chemically is a relatively a simple process for the manufacturer because the plastic pellets have materials compounded into the base plastic that creates gas bubbles during the extrusion process from the thermal heating of the plastic during extrusion.

As the material heats up to temperature a gas is formed so at the exit of the die the pressure drops and the expansion of the gas forms cells that leave voids or air pockets. The cell structure is typically uniform but the ingredients and the compound control the limits of expansion.

Typical expansion rates range from 30 – 40% can be easily achieved and the distribution of cells are relatively uniform with small voids. The only negative possibility and can be of concern is the residue of the expansion chemicals used and the impact that they have on the dielectric properties at high frequencies.

Triple Tandem Extrusion Process

Our triple tandem extrusion process produces a Skin-Foam-Skin structure that allows the foam structure to be encapsulated between two layers of solid material.

This gives LOROM a composite structure that will resist the crushing forces of post processing as well as a better adhesion of the insulating material to the conductor.

Overall this superior insulation structure gives us miniature twin-axial or coaxial products that perform better than foam or foam-skin dielectrics under the mechanical strain of post processing as well as superior transmission performance.

Triple Layer Technologies

Skin-foam-skin dielectric are constructed with triple layer technologies:

1st layer of solid PE skin covering the inner conductor:

• Prevent any undesirable air void close to the center conductor
• Creates good adhesion
• Sealed, elimination of any corrosion

2nd layer physical foam PE gas injected foam dielectric:

• Higher expansion is possible due to the inner and outer skin
• Lower loss and smaller size

3rd layer, solid PE skin, covering the dielectric:

• Stronger geometry, increased crush resistance
• Moisture protrusion eliminated, due to outer skin