Rogers PCB

Which Designs Need Rogers PCB Materials?

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Rogers Corporation is one of the leading electronic circuit board materials manufacturers. Their materials and laminates are primarily used in high-speed and high-frequency PCBs, and they are well known for their line of PTFE-based laminates.

Rogers PCB materials are known for their consistent dielectric constant and higher coefficient of thermal expansion (CTE) compared to other standard PCB materials like FR4. They are also known for having very low losses at high frequencies, and the company is well known for using low-profile copper in their laminate materials. As such, they are often seen as the laminate of choice for high-speed PCBs by newer designers.

In this article, I’ll outline which PCBs are candidates for use of Rogers PCB materials, both in terms of reinforced and unreinforced PTFE laminates. I’ll also discuss when it’s best to use Rogers PCB materials with standard FR4-grade epoxy-resin laminates.

Rogers PCB Materials vs. FR4 PCB Materials

One critical factor that determines the overall performance of a circuit board is the materials in the PCB stackup. Rogers PCB materials are one of many options typically selected for use in RF PCBs, military-grade PCBs, and some high-reliability systems. Here are some of the broad material properties of Rogers PCB materials.

  • They have minimal dielectric loss
  • They are available in unreinforced varieties, which eliminates the fiber weave effect.
  • Greater consistency in dielectric constant vs. frequency (i.e., low dispersion)
  • High Tg value and competitive CTE values
  • Wide range of dielectric constants ranging from approximately 3 to 10

Most PCBs use FR4-grade (Flame Retardant level 4) materials, a National Electrical Manufacturers Association (NEMA) defined standard for glass-reinforced epoxy laminate materials. Above approximately 5-10 GHz, FR4 materials experience excessive dielectric losses. As a result, Rogers materials are now considered an industry standard material in rigid microwave/RF PCBs to ensure consistent operation and signal integrity. However, FR4 materials are still appropriate for standard PCBs as they offer the right mix of durability, performance, and low cost. The table below provides a comparison of Rogers PCB laminates and typical FR4 materials.

 

Rogers PCB

 

To see some other RF material options, take a look at our resource page.

Usage And Design

The excessive dielectric losses in FR4-grade materials, particularly in higher density designs with signal bandwidths reaching up to many GHz, made PCB designers realize they need materials specifically designed for RF systems.

The lower loss of PTFE-based laminates is one reason they are often cited as an essential laminate in high-speed PCBs. You’ll find guidelines throughout the internet attesting to this, as if these laminates are the only option for high-speed systems. The two primary cited reasons include:

  • The lower loss tangent of PTFE-based Rogers PCB materials is needed in high speed systems. In reality, this is only appropriate in insertion-loss-dominant systems, like large backplanes or systems with many SerDes channels with ps rise times.

  • The lower Dk value provides a faster propagation time, so the electrical length will be longer. However, in high-speed design, you should just design to the target interconnect impedance anyways, then you will not have to worry about this.

In reality, there are several reasons to use these materials beyond their lower loss and optional lack of reinforcement. I’ve outlined some of these factors below.

High Density PCBs

When layer counts are thin, the required linewidth needed to hit an impedance target will also be thin. It’s important to hit the impedance target in these systems because channels may be return loss dominated, rather than insertion loss dominated. In these cases, you’ll be forced to use smaller linewidths. The lower Dk value in Rogers PCBs allows for slightly wider linewidths than on FR4 for the same impedance target. This also reduces insertion loss because the skin effect will be reduced.

Cost

The cost of Rogers materials is higher than that of FR4 materials, considering their high quality. In addition, for unreinforced Rogers materials, they are more difficult to work with in thinner layers, which could increase fabrication costs and create a danger of greater misregistration during PCB fabrication. If you have a limited budget and you’re designing a standard PCB, there are low-loss FR4 materials with loss tangents reaching down to 0.01. If performance is the priority, and you’re designing a high-frequency PCB, then Rogers PCB materials may be the best choice.

Absorption and Insulation

Moisture absorption in PCB materials directly affects their thermal and electrical properties. Rogers PCBs have lower absorptivity compared to ordinary PCB laminates, so they can be expected to exhibit greater reliability in certain environmental settings. In terms of electric insulation, Rogers PCB materials are built with ceramic hydrocarbons, resulting in low electrical conductivity but high thermal conductivity and a higher Tg value.

High-Reliability Systems

There are some important areas where Rogers PCB materials are preferred as they produce more reliable PCBAs. Two areas where we work are:

  • Avionics Equipment and Satellites - Avionics equipment and satellites require circuit boards that can withstand thermal/mechanical shocks, thermal cycling to extreme temperatures, and pressure variations. Roger PCBs are perfect for such use cases due to their impressive Tg value as listed above.

  • Telecom Antenna Systems - Rogers materials, with their high performance and low circuit losses at high frequencies, are used in advanced radar systems, military-grade antenna systems, backplanes, and 5G systems. The consistent dielectric constant and minimal circuit losses of Rogers materials make them ideal for telecommunication systems.

Using Rogers PCB Materials With Standard FR4 Materials

Hybrid PCB stackups will incorporate dissimilar materials into the layer stack, such as standard FR4 and a PTFE laminate. Hybrid PCBs typically have a low-loss laminate on one layer, although multiple laminations are possible and the PTFE material can be found on additional layers. If it’s possible to stack all the RF signals on one layer, it would be inefficient to build the entire PCB stackup from more expensive low-loss laminates. You can increase the board size to fit everything properly on only the low-loss layer.

The image below is an example of 6-layer hybrid stackup that could include Rogers on the top layer. This stackup has been used by NWES in multiple radar systems for aerospace and defense clients.

 

Rogers hybrid stackup

ITEQ and Rogers PCB materials mixed in a hybrid stackup. Learn more about this type of PCB stackup construction in my article on Altium Resources.

 

Rogers Microwave/RF PCB Materials Chart

The chart below shows the basic properties of various RF Rogers PCB materials sorted in order of increasing dielectric constant.


*Type: P = PTFE, C = Ceramic, W = Woven, T = Thermoset Resin, R = Random Glass, ME = Modified Epoxy Resin, CE = Cyanate Ester, F = Filled Composite, CEQ = Cyanate Ester w/Quartz Fabric, LCP = Liquid Crystalline Polymer, CP = Cross Plied, H = Hydrocarbon


Dk@10GHz Name Type CTE-X (ppm/°C) CTE-Y (ppm/°C) CTE-Z (ppm/°C) Df@10GHz MIL REF IPC Slash Sheet
1.96 +/- 0.04
RT/Duroid 5880LZ P,F See mfg. See mfg. 41.5 0.0019 - -
2.20 +/- 0.02 RT/Duroid 5880 P,R 31 48 237 0.0009 GP,GR 125/04
2.33 +/- 0.02 RT/Duroid 5870 P,R 22 28 173 0.0012 GP,GR 125/04
2.4 - 2.6 +/- 0.04
Ultralam 2000
P,W 15 15 200 0.0019 GX 125/02
2.90 Ultralam 3850 LCP 17 17 150 0.0025 - -
2.90 - 3.00+/- 0.04 RT/Duroid 6202PR P,C,W 15 15 30 0.0020 - -
2.94 +/- 0.04 RT/Duroid 6002 P,C 16 16 24 0.0012 - -
2.94 +/- 0.04 RT/Duroid 6202 P,C,W 15 15 30 0.0015 - -
3.00 +/- 0.04 RO3003 P,C 17 16 25 0.0011 GX 125/02
3.00 +/- 0.06 RO3730 P,C 11 12 65 0.0016 - -
3.00 +/- 0.08 RO4730 H,C 19 17 40 0.0033
3.02 +/- 0.04 RO3203 P,C,W 13 13 58 0.0016 - -
3.23 +/- 0.05 XT/Duroid 8000 0.002" Thick See mfg. data sht. 18 23 68 0.0035max. - -
3.27 +/- 0.032 TMM-3 C,T 15 15 23 0.0020 - -
3.30 +/- 0.08 RO4533 H,C 13 11 37 0.0025 - -
3.32 +/- 0.05 XT/Duroid 8100 0.004" Thick See mfg. data sht. 19 21 76 0.0038 - -
3.38 +/- 0.05 RO4003C H,C 11 14 46 0.0029 - -
3.39 max. SYRON 7100 0.004" thick. T 19 21 76 0.005max. - -
3.40 +/- 0.08 RO4534 H,C 11 14 46 0.0027 - -
3.4 max. SYRON 7000 0.002" thick T 18 23 68 0.0045max. - -
3.48 +/- 0.05 RO4350B H,C 14 16 35 0.0037 - -
3.48 +/- 0.05 RO4350B -TX H,C 14 16 35 0.0034 - -
3.50 +/- 0.05 RT/Duroid 6035HTC P,C 19 19 39 0.0013 - -
3.50 +/-0.05 RO3035 P,C 17 17 24 0.0017 - -
3.50 +/- 0.08 RO4535 H,C 14 16 35 0.0037 - -
3.54 +/- 0.05 XT/Duroid 8100 0.002" Thick See mfg. data sht. 16.5 18 57 0.0049 - -
3.61 max. SYRON 7100 0.002" thick T 16.5 18 57 0.006max. - -
3.85 – 4.02 Theta See mfg. data sht. N/A N/A ~50 0.0126 – 0.0120 - -
4.50 +/- 0.045 TMM-4 C,T 16 16 21 0.0020 - -
6.00 +/- 0.08 TMM-6 C,T 18 18 26 0.0023 - -
6.15 +/- 0.15 RT/Duroid 6006 P,C 47 34 117 0.0027 - 125/07
6.15 +/- 0.15 RO3006 P,C 17 17 24 0.0020 N/A 125/07
6.15 +/-0.15 RO3206 P,C,W 13 13 34 0.0027 - -
6.15 +/- 0.15 RO4360 H,C 16.6 14.6 30 0.0038 - -
9.20 +/- 0.23 TMM-10 C,T 21 21 20 0.0022 - -
9.80 +/- 0.245 TMM-10i C,T 19 19- 20 0.0020 - -
10.2 +/- 0.30 RO3010 P,C 13 11 16 0.0022 - 125/08
10.2 +/- 0.50 RO3210 P,C,W 13 13 34 0.0027 - -
10.2 +/- 0.25 RT/Duroid 6010.2LM P,C 24 24 47 0.0023 - 125/08

 

NWES is an experienced PCB design firm with RF design and manufacturing expertise. We help aerospace OEMs, defense primes, and private companies in multiple industries design advanced PCBs and create cutting-edge embedded technology. We've also partnered directly with EDA companies and advanced ITAR-compliant PCB manufacturers, and we'll make sure your next high speed digital system is fully manufacturable at scale. Contact NWES for a consultation.

 



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