RT/duroid 5870 and 5880 are related low-Dk PTFE laminate choices. Their most useful comparison starts with the dimensions and performance of the finished circuit, because even a modest dielectric difference changes an electrically long structure.
Keep the electrical objective constant
Choose the same target impedance, band and electrical length for both candidates. Recalculate width and length using a justified dielectric input, then inspect the resulting layout. An antenna designed for one grade may need retuning on the other. Using identical artwork is appropriate for a substitution-risk experiment, but it is not a fair comparison of two optimized designs.
Check the offered construction
The 5870 and 5880 grade pages identify sourced material information. Confirm the dielectric thickness, tolerance and foil at the time of procurement. A thin construction may be more sensitive to copper geometry and handling than a thicker one. Compare these details before treating the two material names as a simple purchasing alternative.
Example: a long phase reference
For a delay line or phase-reference path, calculate the nominal electrical length and then examine sensitivity to thickness and dielectric variation. A small percentage change in effective permittivity accumulates across a long route. Use the wavelength and phase tool with the effective dielectric constant of the transmission line, not an unexamined bulk Dk. Verify the actual line with a calibrated measurement and a defined temperature.
Evaluate loss in the same fixture
When lower attenuation is the reason for the comparison, use equivalent impedance, copper surface and launch quality. Measure more than one line length if the test method allows separation of propagation and transitions. Document sample handling and support, especially around connectors. Assess the total performance margin and manufacturing repeatability before approving an alternative. If the circuit already meets its limits, preserving a characterized construction may have more value than chasing a small nominal datasheet advantage.
For replacement approval, document whether line dimensions are frozen or may be retuned. If artwork must remain unchanged, evaluate the resulting mismatch directly and set a functional acceptance limit. If redesign is permitted, compare the optimized result without describing it as a drop-in substitution.
Source-aware property comparison
RT/duroid 5870
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 2.33 ± 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 | 2.33 | Typical, 8–40 GHz; differential phase length method. Average across the common constructions in the cited datasheet. Source |
| Dissipation factor | 0.0012 | Typical; 10 GHz, C24/23/50; IPC-TM-650 2.5.5.5, Z direction. Source |
| Thermal conductivity | 0.22 W/(m·K) | Typical; ASTM C518, 80°C; through-thickness thermal conduction. Source |
| CTE, X axis | 22 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.4.41. Source |
| CTE, Y axis | 28 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.4.41. Source |
| CTE, Z axis | 173 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.4.41. Source |
| Thermal coefficient of dielectric constant | -115 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.
RT/duroid 5880
| 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.
Treat the choice as a geometry, phase and repeatability decision, and avoid uncontrolled artwork substitution.