LAMINATES: DK, DF AND TRACE WIDTH
What are the Dk and Df of Arlon 85N?
Arlon 85N has a dielectric constant (Dk) of 4 and a loss factor (Df) of 0.015 at 10 GHz, as published by its maker. A 50 ohm surface microstrip over a 0.2 mm dielectric comes out about 0.380 mm wide on it, against 0.353 mm on standard FR-4.
- The nearest grade in the catalogue by Dk is Panasonic Megtron 4, at Dk 3.8 and Df 0.007 at 10 GHz.
- Dielectric loss on that microstrip is about 0.525 dB per inch at 10 GHz, and the signal travels at about 146 ps per inch.
- Buried as a stripline between planes 0.4 mm apart, 50 ohms needs a trace about 0.139 mm wide.
50 ohm surface microstrip, 1 oz copper
| Dielectric height | Trace width on 85N | On standard FR-4 |
|---|---|---|
| 0.1 mm | 0.179 mm | 0.166 mm |
| 0.2 mm | 0.380 mm | 0.353 mm |
| 0.5 mm | 0.989 mm | 0.920 mm |
| 1.6 mm | 3.24 mm | 3.02 mm |
As published
| Property | Value |
|---|---|
| Type | Pure Polyimide |
| Tg (°C) | >250 |
| Td (°C) | 407 |
| Dk @ 10 GHz | ~4.0 |
| Df @ 10 GHz | ~0.015 |
| Key Application | Aerospace, burn-in, downhole |
Nearest grades in the catalogue by Dk at 10 GHz
| Laminate | Dk | Df | Tg |
|---|---|---|---|
| Panasonic Megtron 4 | 3.8 | 0.007 | 210 (DMA) |
| Nelco Meteorwave 1000 | 3.7 | 0.0055 | not published |
| Rogers Kappa 438 | 4.38 | 0.005 | not published |
How this was counted
Dk and Df are the maker's published values at 10 GHz, from the MPBxChange material catalogue, which keeps each source's test frequency and method. Where a maker publishes a range, the midpoint is used. Widths are solved with the Hammerstad and Jensen microstrip equations and Wadell's stripline form, for 1 oz copper, and are a starting point: Dk moves with frequency, resin content and glass style, and a fabricator's field solver is the authority. Standard FR-4 here is the median of 22 FR-4 grades in the catalogue (Dk 4.4).