PCB material selection is a crucial component in the performance of a circuit assembly. In the past, typically FR4 was specified. But, with high-speed designs, the use of the correct laminate is critical. The use of a material with a lower dielectric constant (Dk) is advisable and preferred. This not only ensures the best signal performance, but it will also minimize any signal distortion or phase jitter of the signal.
- Mechanical strength
- Thermal characteristics
- Electromagnetic loss
- Environmental stability of the material in varying humidity and temperature settings
- RF-power handling capability
- Compatibility and use in hybrid constructions
- Cost
Rogers RO4350B Laminates
The Rogers RO4350B laminates provide a low dissipation factor (Df), which boosts the power delivered and therefore enables high-power applications. Also, their low dielectric constant (Dk) permit rapid signal propagation. RO4350B laminates do not call for the special through-hole treatments or handling procedures as PTFE based materials. These materials are UL 94 V-0 rated for active devices and high power RF designs.
Summary of features:
- Dk of 3.48 +/- 0.05
- Dissipation factor of 0.0037 at 10 GHz
- Low Z-axis coefficient of thermal expansion at 32 ppm/°C
Benefits
- Processes like FR-4 at lower fabrication cost
- Competitively priced
- Excellent dimensional stability
Standard Thickness:
- 0.004” ( not available in panel sizes larger than 24”x18”)
- 0.0066”
- 0.010”
- 0.0133”
- 0.0166”
- 0.020”
- 0.030”
Panasonic MEGTRON6 – R-5775 Laminates
The MEGTRON6 laminates are high speed, ultra-low loss materials with impressive HDI and thermal performance
Summary of features:
- Dk 3.4, Df 0.004@12GHz
- Tg (DMA) 185°C
- T288(with copper) >120min.
Find out the main differences between 2 of the most commonly used high-frequency, high-speed laminates; Rogers 4350B and Panasonic Megtron 6.
Property | Rogers RO4350B | Condition | Test Method | Panasonic R-5775(N) – Low Dk glass cloth version | Panasonic R-5775 – Normal glass cloth | Test Method |
Dielectric Constant (Dk) | 3.48 ± 0.05 | 10 GHz/23°C | IPC-TM-650 2.5.5.5 Clamped Stripline |
3.40 (@1 GHZ) 3.35 (@12 GHZ) |
3.6 (@12 GHZ) | IPC-TM-650 2.4.24.1 |
Dissipation Factor tan (Df) | 0.0037 0.0031 |
10 GHz/23°C 2.5 GHz/23°C |
IPC-TM-650 2.5.5.5 |
0.002 (@1 GHZ) 0.004 (@12 GHZ) |
0.002 (@1 GHZ) 0.004 (@12 GHZ) |
IPC-TM-650 2.5.5.9 |
Thermal Coefficient | +50 ppm/°C | -50°C to 150°C | IPC-TM-650 2.5.5.5 | 45 ppm/°C | 45 ppm/°C | IPC TM-650 2.4.24 |
Volume Resistivity | 1.2 X 1010 MΩ•cm | COND A | IPC-TM-650 2.5.17.1 | 1 X 109MΩ•cm | 1 X 109MΩ•cm | IPC TM-650 2.5.17.1 |
Surface Resistivity | 5.7 X 108 MΩ | COND A | IPC-TM-650 2.5.17.1 | 1 X 108MΩ | 1 X 108MΩ | IPC TM-650 2.5.17.1 |
Electrical Strength | Z- axis 31.2 KV/mm | 0.51mm (0.020”) | IPC-TM-650 2.5.6.2 | |||
Tensile Modulus | X- 16,767 MPa X- 14,153 MPa |
RT | ASTM D638 | 18,000 | 19,000 | JIS C 6481 |
Tensile Strength | X- 203 MPa Y- 130 MPa |
RT | ASTM D638 | |||
Flexural Strength | 255 MPa | IPC-TM-650 2.4.4 | ||||
Dimensional Stability | <0.5 mm/m | after etch +E2/150°C |
IPC-TM-650 2.4.39A | |||
Coefficient of Thermal Expansion(X) | 10 ppm/°C | -55 to 288°C | IPC-TM-650 2.4.41 | 14-16 @ 260°C | 14-16 @ 260°C | IPC-TM-650 2.4.24 |
Coefficient of Thermal Expansion(Y) | 12 ppm/°C | -55 to 288°C | IPC-TM-650 2.4.41 | 14-16 @ 260°C | 14-16 @ 260°C | IPC-TM-650 2.4.24 |
Coefficient of Thermal Expansion(Z) | 32 ppm/°C | -55 to 288°C | IPC-TM-650 2.4.41 | 45 @ 260°C | 45 @ 260°C | IPC-TM-650 2.4.24 |
Tg | >280 °C TMA | A | IPC-TM-650 2.4.24.3 | 185 | 185 | DSC |
Td | 390 °C TGA | ASTM D3850 | 410 | 410 | TGA | |
Thermal Conductivity | 0.69 W/m/°K | 80°C | ASTM C518 | |||
Moisture Absorption | 0.06% | 48 hrs immersion 0.060” sample Temperature 50°C |
ASTM D570 | 0.14% | 0.14% | IPC-TM-650 2.6.2.1 0.030″ sample |
Density | 1.86 gm/cm3 | 23°C | ASTM D792 | |||
Copper Peel Strength | 0.88 N/mm | after solder float 1 oz. EDC Foil | IPC-TM-650 2.4.8 | 0.8 kN / m | 0.8 kN / m | IPC-TM-650 2.4.8 |
Flammability | 94V-0 | UL 94 | 94V-0 | UL 94V-0 | ||
Lead-Free Process Compatible | Yes | |||||
Time to delamination at 288°C with copper | >120 min | >120 min | IPC-TM-650 2.4.24.1 |
In sum
As a part of the design process, PCB designers need to specify materials that offer an optimal or near-optimal price-performance ratio. To achieve this task PCB materials need to be researched, analyzed, evaluated, and selected.