The Importance of choosing the correct RF PCB Material
Selecting the PCB substrate material is a critical performance factor when designing PCBs for RF applications.
The optimal combination of electrical and mechanical attributes is required for complex microwave structures which are mechanically reliable and electrically stable.
An extremely low thermal coefficient of dielectric constant provides the electrical stability sought after by designers of filters, oscillators, and delay line applications.
Taconic, ISOLA, and Rogers all manufacture PCB laminate materials designed for high-performance, high-speed/RF/microwave applications.
Factors to consider when choosing an RF PCB material
A low Z-axis coefficient of thermal expansion (CTE) is necessary for the superior reliability of plated through-holes.
To achieve a narrow range of positional tolerances, it is imperative to match the X and Y coefficient expansion of the PCB substrate to copper.
Increasing surface mount reliability by reducing stress at solder joints and allowing the expansion of the PCB laminate up to the minimum amount of low CTE is a benefit of a material with low tensile modulus.
- thermal performance
- low dissipation factor (Df)
- stable Df characteristics
- low Z-axis Coefficient of Thermal Expansion (CTE)
- skew mitigation properties
- characteristics to improve rise times
- jitter reduction
- conductor loss reduction
One of the key characteristics of high-frequency laminate material is the stability of the dissipation factor (Df) since this will tell you how signal losses occur and their distribution across the frequency band of operation.
Also, a stable dielectric constant (Dk) and consequently a stable impedance across the length and width of a substrate is important.
High-frequency laminates display little change in the Dk with variations in temperature over a wide range.
In an RF or microwave circuit, the value of the dielectric constant will impact the PCB’s trace sizes and therefore the size of the PCB. Higher Dk PCB materials can result in smaller PCBs.
The table below displays the key electrical and mechanical attributes of the Taconic, ISOLA, and Rogers for ease of comparison.
PCB Material Comparison table – Part 1 of 5
| Manufacturer | Taconic | Taconic | Taconic |
| Product | TLX-6,7,7,9,0 | TLY-5 | RF35 |
| Material Type | PTFE / Glass | PTFE / Glass | PTFE / Glass |
| Lead-Free Process Compatible | Yes | Yes | Yes |
| Halogen Free | No | No | No |
| Flammability UL94 | V-0 | V-0 | V-0 |
| Glass Transition Temp Tg Celcius |
|||
| Td (Decomposition Temp) by TGA – ºC | |||
| Dk 1 GHz | |||
| Dk 2-3 GHz | 3.5 (±0.10) | ||
| Dk 10-12 GHz | 2.45-2.65 (±0.04) | 2.2 (±0.03) | |
| Df 1 GHz | |||
| Df 2-3 GHz | 0.0012 | 0.002 | |
| Df 10-12 GHz | 0.00155 – 0.0021 | 0.0009 | |
| Moisture Absorption (%) | 0.02% | 0.02% | 0.02% |
| CTE X-Axis (PPM/ºC) Pre Tg | 21 | 26 | 19 |
| CTE Y-Axis (PPM/ºC) Pre Tg | 23 | 15 | 24 |
| CTE Z-Axis (ppm/ºC) Pre Tg | 215 | 217 | 64 |
| Material Considered | RF | RF | RF |
| Peel Strength – 1oz (35μm) – N/mm | 2.1 | 3.04 | 1.5 |
| T260 | |||
| T288 – minutes | |||
| Flexural strength – N/mm2 | X – 199 Y – 142 |
X – 96.1 Y – 89.32 |
X – 152 Y – 124 |
| Young’s modulus – N/mm2 | X – 6,757 Y – 8,274 |
9.65 x 103 | |
| Tensile strength – N/mm2 | X – 245 Y – 190 |
X – 187 Y – 145 |
|
| Volume Resistivity – MΩ/cm | 1.110 x 1010 | 1×1010 | 1.26×109 |
| Dielectric strength – V | 45,000 | 106,023 | |
| Surface Resistivity – MΩ/cm | 6.605 x 108 | 1×108 | 1.46×108 |
| Dimensional stability – mm/M | -0.038 | ||
| Thermal Conductivity – W/mK | 0.14 – 0.22 | 0.22 | 0.32 |
PCB Material Comparison table – Part 2 of 5
| Manufacturer | Taconic | Taconic | Isola |
| Product | RF35TC | TSM-DS3 | Astra MT77 |
| Material Type | PTFE / Glass | PTFE / Glass | PPE Blend |
| Lead Free Process Compatible | Yes | Yes | Yes |
| Halogen Free | No | No | No |
| Flammability UL94 | V-0 | V-0 | |
| Glass Transition Temp Tg Celcius |
200 | ||
| Td (Decomposition Temp) by TGA – Celcius | 420 | 526 | 360 |
| Dk 1 GHz | |||
| Dk 2-3 GHz | 3 | ||
| Dk 10-12 GHz | 3.5 (±0.05) | 3 (±0.05) | 3 |
| Df 1 GHz | |||
| Df 2-3 GHz | 0.002 | ||
| Df 10-12 GHz | 0.0011 | 0.0011 | 0.002 |
| Moisture Absorption (%) | 0.05% | 0.07% | 0.10% |
| CTE X-Axis (PPM/ºC) Pre Tg | 11 | 10 | 12 |
| CTE Y-Axis (PPM/ºC) Pre Tg | 13 | 16 | 12 |
| CTE Z-Axis (ppm/ºC) Pre Tg | 34 | 23 | 50-70 |
| Material Considered | RF | RF | RF |
| Peel Strength – 1oz (35μm) – N/mm | 1.23 | 1.46 | 1 |
| T260 | >60 | ||
| T288 – minutes | >60 | ||
| Flexural strength – N/mm2 | X – 88.94 Y – 80.67 |
X – 81 Y – 51 |
X – 338 Y – 269 |
| Young’s modulus – N/mm2 | X – 4,599 Y – 4,392 |
X – 6,708 Y – 6,784 |
|
| Tensile strength – N/mm2 | X – 62.19 Y – 53.37 |
X – 48 Y – 26 |
X – 214 Y – 165 |
| Volume Resistivity – MΩ/cm | 5.19 x 108 | 1.1 x 107 | 1.33 x 107 |
| Dielectric strength – V | 22,441 | 21,575 | 45,400 |
| Surface Resistivity – MΩ/cm | 6.42 x 107 | 2.3 x 106 | 1.33 x 105 |
| Dimensional stability – mm/M | |||
| Thermal Conductivity – W/mK | 0.92 | 0.65 | 0.45 |
PCB Material Comparison table – Part 3 of 5
| Manufacturer | Rogers | Rogers | Rogers |
| Product | RT/duroid 5870 | RT/duroid 5880 | RT/duroid 6002 |
| Material Type | PTFE /Glass | PTFE / Glass | Ceramic / PTFE |
| Lead Free Process Compatible | Yes | Yes | Yes |
| Halogen Free | No | No | No |
| Flammability UL94 | V-0 | V-0 | V-0 |
| Glass Transition Temp Tg Celcius |
|||
| Td (Decomposition Temp) by TGA – Celcius | 500 | 500 | 500 |
| Dk 1 GHz | |||
| Dk 2-3 GHz | |||
| Dk 10-12 GHz | 2.33 (±0.02) | 2.2 (±0.02) | 2.94 (±0.04) |
| Df 1 GHz | 0.0005 (1MHz) | 0.0004 (1MHz) | |
| Df 2-3 GHz | |||
| Df 10-12 GHz | 0.0012 | 9E-04 | 0.001 |
| Moisture Absorption (%) | 0.02% | 0.02% | 0.02% |
| CTE X-Axis (PPM/ºC) Pre Tg | 22 | 31 | 12 |
| CTE Y-Axis (PPM/ºC) Pre Tg | 28 | 48 | 16 |
| CTE Z-Axis (ppm/ºC) Pre Tg | 173 | 237 | 24 |
| Material Considered | RF | RF | RF |
| Peel Strength – 1oz (35μm) – N/mm | 4.8 | 5.5 | 1.6 |
| T260 | |||
| T288 – minutes | |||
| Flexural strength – N/mm2 | |||
| Young’s modulus – N/mm2 | |||
| Tensile strength – N/mm2 | 1,300 1,280 (@ 23 ºC) |
1,070 860 (@ 23 ºC) |
828 (@ 23 ºC) |
| Volume Resistivity – MΩ/cm | 2×107 | 2×107 | 1×106 |
| Dielectric strength – V | |||
| Surface Resistivity – MΩ/cm | 2×107 | 3×107 | 1×107 |
| Dimensional stability – mm/M | |||
| Thermal Conductivity – W/mK | 0.22 (@ 80 ºC) | 0.20 (@ 80 ºC) | 0.60 (@ 23 ºC) |
PCB Material Comparison table – Part 4 of 5
| Manufacturer | Rogers | Rogers | Rogers |
| Product | RT/duroid 6006 | RT/duroid 6010.2LM |
RT/duroid 6202 |
| Material Type | Ceramic / PTFE | Ceramic / PTFE | Ceramic / PTFE |
| Lead Free Process Compatible | Yes | Yes | Yes |
| Halogen Free | No | No | No |
| Flammability UL94 | V-0 | V-0 | V-0 |
| Glass Transition Temp Tg Celcius |
|||
| Td (Decomposition Temp) by TGA – Celcius | 500 | 500 | 500 |
| Dk 1 GHz | |||
| Dk 2-3 GHz | |||
| Dk 10-12 GHz | 6.15 (±0.15) | 10.2 (±0.25) | 2.94 ± 0.04 |
| Df 1 GHz | |||
| Df 2-3 GHz | |||
| Df 10-12 GHz | 0.0027 | 0.0023 | 0.002 |
| Moisture Absorption (%) | 0.05% | 0.01% | 0.10% |
| CTE X-Axis (PPM/ºC) Pre Tg | 47 | 24 | 15 |
| CTE Y-Axis (PPM/ºC) Pre Tg | 34 | 24 | 15 |
| CTE Z-Axis (ppm/ºC) Pre Tg | 117 | 47 | 30 |
| Material Considered | RF | RF | RF |
| Peel Strength – 1oz (35μm) – N/mm | 2.5 | 2.1 | 1.6 |
| T260 | |||
| T288 – minutes | |||
| Flexural strength – N/mm2 | X – 2634 Y – 1951 |
X – 4364 Y – 3751 |
|
| Young’s modulus – N/mm2 | X – 627 Y – 517 |
X- 931 Y – 559 |
|
| Tensile strength – N/mm2 | 1007 | ||
| Volume Resistivity – MΩ/cm | 2×107 | 5×105 | 1×106 |
| Dielectric strength – V | |||
| Surface Resistivity – MΩ/cm | 7×107 | 5×106 | 1×109 |
| Dimensional stability – mm/M | |||
| Thermal Conductivity – W/mK | 0.49 (@ 80ºC) | 0.86 (@ 80ºC) | 0.68 |
PCB Material Comparison table – Part 5 of 5
| Manufacturer | Rogers | Rogers | Rogers | Rogers |
| Product | RO3210 | RO3003 | TMM-3 | TMM-10 |
| Material Type | Ceramic / PTFE | Ceramic / PTFE | Ceramic, hydrocarbon, thermoset polymer | Ceramic, hydrocarbon, thermoset polymer |
| Lead Free Process Compatible | Yes | Yes | Yes | Yes |
| Halogen Free | No | No | No | No |
| Flammability UL94 | V-0 | V-0 | ||
| Glass Transition Temp Tg Celcius |
||||
| Td (Decomposition Temp) by TGA – Celcius | 500 | 500 | 425 | 425 |
| Dk 1 GHz | ||||
| Dk 2-3 GHz | ||||
| Dk 10-12 GHz | 10.2 ± 0.50 | 3 ± 0.04 | 3.27 ± 0.032 | 9.2 ±0.230 |
| Df 1 GHz | ||||
| Df 2-3 GHz | ||||
| Df 10-12 GHz | 0.0027 | 0.001 | 0.002 | 0.0022 |
| Moisture Absorption (%) | <0.1% | 0.04% | 0.06% | 0.09% |
| CTE X-Axis (PPM/ºC) Pre Tg | 13 | 17 | 15 | 21 |
| CTE Y-Axis (PPM/ºC) Pre Tg | 16 | 15 | 21 | |
| CTE Z-Axis (ppm/ºC) Pre Tg | 34 | 25 | 23 | 20 |
| Material Considered | RF | RF | RF | RF |
| Peel Strength – 1oz (35μm) – N/mm | 11 | 2.22 | ||
| T260 | ||||
| T288 – minutes | ||||
| Flexural strength – N/mm2 | 1.72 | 1.79 | ||
| Young’s modulus – N/mm2 | ||||
| Tensile strength – N/mm2 | x – 3992 y – 3565 |
x – 930 y – 823 |
||
| Volume Resistivity – MΩ/cm | 1×103 | 1×107 | 3×109 | 2×108 |
| Dielectric strength – V | 441 | 285 | ||
| Surface Resistivity – MΩ/cm | 1×103 | 1×107 | >9X109 | 4×107 |
| Dimensional stability – mm/M | x- -0.06 y – 0.07 |
|||
| Thermal Conductivity – W/mK | 0.81 | 0.5 | 0.7 | 0.76 |