RT/duroid 5880 is a random-glass-fiber PTFE laminate frequently considered for low-loss microwave and antenna structures. Its low dielectric constant supports relatively wide lines and larger electrical structures than higher-Dk substrates. Those geometric consequences can be useful, but must be evaluated in the space available for the circuit.
Material system
PTFE reinforced with random glass fibers
Technical properties
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 2.20 ± 0.02 | Specification-labelled process Dk; 10 GHz, C24/23/50; IPC-TM-650 2.5.5.5, Z direction. Datasheet footnote 1 describes 1 oz ED copper acceptance testing. Source |
| Design dielectric constant | 2.2 | Typical, 8–40 GHz; differential phase length method. Average across the common constructions in the cited datasheet. Source |
| Dissipation factor | 0.0009 | Typical; 10 GHz, C24/23/50; IPC-TM-650 2.5.5.5, Z direction. Source |
| Thermal conductivity | 0.2 W/(m·K) | Typical; ASTM C518, 80°C; through-thickness thermal conduction. Source |
| CTE, X axis | 31 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.4.41. Source |
| CTE, Y axis | 48 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.4.41. Source |
| CTE, Z axis | 237 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.4.41. Source |
| Thermal coefficient of dielectric constant | -125 ppm/°C | Typical; -50°C to 150°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); 10 GHz. Source |
Typical reported values are not a purchase specification. Process Dk, design Dk and values measured at different frequencies are not interchangeable.
Selection and design notes
- Consider it for a long RF path when the lower dielectric-loss contribution is valuable and the fabricator can support PTFE processing. Compare total line loss with the selected foil and width, because the Df number alone excludes conductor and launch losses.
- For an antenna, optimize thickness and footprint together. A low-Dk material does not remove the need to model the ground plane, enclosure and nearby conductors.
Thickness and copper options
The datasheet lists 5, 10, 20, 31 and 62 mil cores; choose the tolerance belonging to the actual thickness.
ED and rolled copper are separate options. Copper roughness and finished plating must be specified for meaningful loss predictions.
Fabrication considerations
- Specify ED or rolled foil and require the manufacturer's qualified PTFE drilling and plating preparation. For bonded multilayers, assess the bond film's temperature limits and dielectric effect rather than assuming the core controls the whole structure.
Application fit
- Low-loss antennas
- Microwave transmission lines
- RF measurement coupons
Limits and substitution checks
- The material's low thermal conductivity is not a heat-spreading solution. Its Z-axis expansion and temperature-dependent permittivity can matter in multilayers and precision phase networks. RT/duroid 5880LZ is a different filled composite, not a lighter version with identical RF properties.