All about TACONIC material RF-35 PCB Manufacturing

Introduction

Taconic RF-35 is a popular high frequency laminate material designed for performance-driven RF PCB applications. With a dielectric constant of 3.5, low loss, and tight material uniformity, RF-35 enables excellent signal integrity for today’s high speed digital and analog circuits.

This article provides an in-depth look at RF-35 material properties, performance capabilities, design considerations, and applications. We’ll explore everything engineers need to know about specifying and working with this versatile RF material.

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RF-35 Overview

Taconic RF-35 is a PTFE composite laminate comprised of:

Woven fiberglass reinforcement
Ceramic filler particles
PTFE (polytetrafluoroethylene) resin system

With a dielectric constant of 3.5, it provides:

Excellent high frequency signal performance
Very low loss characteristics
Tight dielectric constant tolerance

RF-35’s properties make it suitable for a wide range of radio frequency, microwave, millimeter-wave, and multi-gigabit digital applications. It strikes an optimal balance between cost and high frequency signal integrity.

Some key traits of Taconic RF-35 include:

Dielectric constant of 3.5 +/- 0.05
Low loss with tight uniformity
Excellent thermal stability
Good CTE for reliability
Lead-free compatible
US laminator source
ITAR free
RoHS compliant
Cost-effectiveness

For designs from 10+ Gbps digital to Ku band RF, RF-35 delivers proven results across countless commercial and defense programs.

Material Properties

RF-35 is formulated from PTFE reinforced with ceramic particles to achieve:

Dielectric Constant – The k-value determines velocity of signal propagation and affects many circuit parameters. RF-35 provides an Er of 3.5 with very tight +/- 0.05 tolerance for consistent performance. This enables excellent impedance control compared to typical FR-4 (Er=4.5).

Loss Tangent – With a loss tangent of just 0.0019, RF-35 provides very low loss for high frequency energy. This maximizes Q factors in resonant circuits and insertion loss in transmission lines. Wide range of tested Dk from DC to Ku band.

Moisture Absorption – At just 0.02% moisture absorption, RF-35 resists detrimental effects of humidity and water ingress far better than conventional FR-4 material. This enhances long term reliability.

Thermal Performance – With a Z-axis CTE of 82 ppm/C, close PCB/laminate CTE matching reduces stresses under temperature cycling for excellent reliability. Good thermal conductivity (0.71 W/mK) spreads heat.

Lead-Free Assembly – RF-35 achieves high Tg (>280C) allowing compatibility with lead-free solder profiles of up to 260C for modern assembly.

Available Forms

RF-35 laminate allows flexibility through different standard offerings:

Copper Cladding

1⁄2, 1, and 2 oz ED copper foil
Standard HTE copper and rolled copper available
Double-sided cladding enables signal layers

Core Thicknesses

From 0.005 inches to 0.125 inches
Typical stackups use multiple 0.005″ cores
Thicker cores provide rigidity when needed

Panel Sizes

18” x 24”, 18” x 36”, and 24” x 36” standard panels
Custom panel sizes possible

Prepreg

106 and 1067 styles available
Enables bonding multilayer board stackups
Matching resin system

Rod and Plate

For machined parts, spacers, and non-PCB applications
Reduces PIM in RF assemblies
Ideal for fixtures and testing

This range covers the needs of most RF-35 PCB implementations from prototyping to production.

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PCB Performance Capabilities

RF-35 laminate provides excellent RF and high speed digital performance when designed properly:

Frequency Range

Usable continuous range from DC to Ku band (18 GHz)
Material characterizations up to 40+ GHz
Q factors exceeding 300 above 8 GHz

Loss

Low loss tangent of 0.0019
Insertion loss < 0.016 dB/inch at 20 GHz in 50Ω stripline

VSWR

Tight dielectric constant tolerance enables excellent impedance control
VSWR < 1.2 up to 15 GHz achievable

Propagation Delay

Delay = 1.7 ns/inch typical at 50Ω
Enables high data rates and rise time performance

Pulse Response

TDR shows minimal discontinuities and reflections
Clean time domain performance for ultra high-speed digital

Leveraging these attributes allows RF-35 PCBs to deliver highly repeatable RF and high speed digital operation.

Design Considerations

To obtain maximum benefit from RF-35 laminates, engineers should follow best design practices:

Stackup Planning

Use multiple thinner cores instead of one thick core
Alternating grain direction improves dimensional stability
Model expected performance in solver

Impedance Control

Leverage precise Er of 3.5 to maintain target impedance
50Ω striplines for RF and high-speed routing
Controlled line width, dielectric height, trace geometry

Skin Effect

Consider skin effect depth above ~ 8-10 GHz
Utilize surface treatments like micro-etching

Signal Coupling

Careful gap/spacing rules between traces
Ground plane isolation techniques
Avoid 90 ̊ bends; use arc/tapered geometries

Thermal Management

Ensure sufficient thermal ground plane spreading
Efficient component layout to avoid hotspots
Consider thermal vias for heat transfer

Paying attention to these guidelines helps achieve first-pass PCB layout success with RF-35.

Recommended Stackups

Typical RF-35 PCB stackups may use configurations like:

Show Image

Multiple thin dielectric cores
Signal routing on surface layers
Dedicated ground planes near signals
Buried capacitance within stackup
Component cavities in ground planes

The thin cores and smooth copper foils of RF-35 enable tight impedance tolerance and high performance interconnects between ICs, filters, amplifiers, control logic, and other components.

Benefits vs. FR4

Compared to conventional FR-4 laminates, RF-35 provides:

Superior Loss Characteristics

Lower loss tangent: 0.0019 vs 0.02 for FR-4
Much flatter loss vs. frequency curve
Maintains low loss to > 10 GHz

Tighter Dielectric Constant Tolerance

Tolerance +/- 0.05 vs +/- 0.25 for FR-4
Enables consistent impedance across PCBs

Improved Moisture Resistance

0.02% moisture absorption vs 0.2% for FR-4
Far less susceptible to humidity effects

Higher Frequency Support

Usable range to Ku band vs drop-off around 5 GHz with FR-4
Significantly better Q factors at high microwave bands

For peak signal integrity at microwave and mmWave frequencies, RF-35 is a clear choice over FR-4 material.

Typical RF-35 Applications

The capabilities of RF-35 make it a frequent choice for products including:

Satellite communications
Radar and remote sensing
5G telecom infrastructure
Automotive radar
Wireless networking
Microwave radio/links
Defense electronics
Mobile devices
High speed digital design
Aerospace and avionics

Any application where optimizing signal integrity, reducing loss, and maintaining consistent performance over frequency are critical requirements will benefit from RF-35 PCB material.

Pros and Cons

Like any material, RF-35 has both advantages and disadvantages:

Pros

Excellent high frequency signal integrity
Low loss PTFE material
Tight dielectric constant tolerance
Lead-free assembly compatible
Good thermal conductivity
Reduced moisture absorption

Cons

Higher cost than FR-4
Lower flexural strength than glass-reinforced laminates
Requires advanced fabrication processes
Limited global supply chain

Conclusion

With its precise dielectric constant of 3.5 and low loss PTFE composition, Taconic RF-35 delivers proven performance for today’s emerging RF, microwave, and multi-gigabit digital designs. When engineered properly, RF-35 PCBs provide consistent behavior across fabrication lots and excellent high frequency response. For designers pursuing every last dB of loss or GHz of bandwidth, RF-35 remains an enabling material.

Frequently Asked Questions

Q: What are the key differences between RF-35 and common FR-4 laminates?

A: RF-35 provides much lower loss, tighter dielectric tolerance, lower moisture absorption, and extended high frequency range versus economical FR-4.

Q: What are some tips for working with thinner RF-35 cores?

A: Use dedicated layer alignment equipment, employ smaller component sizes, plan sufficient panelization spacing, and minimize handling to avoid cracking thin cores.

Q: Does RF-35 require special PCB fabrication processes?

A: RF-35 benefits from advanced PTFE processes for via formation, hole walls, and drilling. It also requires lamination processes tailored to thinner cores.

Q: What are typical finished RF-35 PCB thicknesses?

A: High frequency designs aim for overall PCB thickness under 0.030 inches. This requires precision lamination of multiple 0.005 inch dielectric cores.

Q: Are there lead-free soldering implications with RF-35 material?

A: RF-35 achieves high Tg (>280C) for compatibility with lead-free profiles up to 260C peak temperatures. Thermal relief in multilayers is recommended.

Do you know RF-35 (TACONIC material)?

Performance:

(1) low cost;

(2) Excellent peel strength;

(3) Extraordinary low loss factor;

(4) low water absorption rate;

(5) Enhanced surface smoothness.

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Application:

(1) power amplifier;

(2) filters and connectors;

(3) Passive components.

1)RF-35 is an organic-ceramic laminate material in the ORCER of TACONIC products.

2)It is a reinforced glass material based on woven glass cloth, and a combination of TACONIC’s ceramic filling technology and glass fiber coated PTFE technology.

3)RF-35 is the best choice for low cost, high volume commercial microwave and wireless frequency applications.

3)RF-35 of 1/20Z and 10Z copper foil boards, even with standard epoxy materials, have excellent peel strength and provide rework at any time.

4)The glass transition temperature of RF -35 exceeds 315 ℃.

5)The ultra-low water absorption and low loss factor of RF-35 minimizes phase shift in the frequency range of use.

6)The dimensional stability of RF-35 is due to the use of woven glass cloth in its design development.

7)RF-35 laminate material, generally with single or double-sided 1/20Z, 10Z and 20Z thickness of electrolytic copper foil. Different sizes of sheets can be selected according to requirements.

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8)For the RF-35 microwave material, the relationship between the thermal expansion rate in the Z-axis direction and the temperature is shown in the figure below: