AD255C-IM combines the AD255C PTFE substrate concept with Rogers' IM copper cladding. The change targets antenna intermodulation behavior and comes with its own dielectric characterization. The IM suffix should remain visible in material records because the published Design Dk and Df differ from those of the base AD255C entry.
Material system
Woven-glass-reinforced PTFE with IM copper cladding
Technical properties
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 2.55 | Typical; 10 GHz, 23°C/50% RH; IPC-TM-650 2.5.5.5 clamped stripline; direction is not separately recorded here. Source |
| Design dielectric constant | 2.58 | Typical; 10 GHz, microstrip differential phase length method, C-24/23/50 conditioning. Source |
| Dissipation factor | 0.0014 | Typical; 10 GHz, 23°C/50% RH; IPC-TM-650 2.5.5.5; direction is not separately recorded here. Source |
| Thermal conductivity | 0.35 W/(m·K) | Typical, through thickness; ASTM D5470. The product table does not state test temperature. Source |
| CTE, X axis | 34 ppm/°C | Typical; -55°C to 288°C, IPC-TM-650 2.4.41; average expansion over the interval, not necessarily linear. Source |
| CTE, Y axis | 26 ppm/°C | Typical; -55°C to 288°C, IPC-TM-650 2.4.41; average expansion over the interval, not necessarily linear. Source |
| CTE, Z axis | 196 ppm/°C | Typical; -55°C to 288°C, IPC-TM-650 2.4.41; average expansion over the interval, not necessarily linear. Source |
| Thermal coefficient of dielectric constant | -110 ppm/°C | Typical; 0°C to 100°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); 10 GHz. Source |
| Water absorption | 0.03 % | Typical; E1/105 + D48/50, IPC-TM-650 2.6.2.1; 60 mil reference construction. 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 an antenna feed with a defined PIM requirement and a measurement plan capable of separating laminate behavior from connector and assembly effects. Specify the IM copper, not merely an AD255C core with unspecified smooth foil.
- Compare the two grades using the same line geometry, thickness and finish. A copper-related improvement cannot be quantified by replacing only Df in a transmission-line calculation.
Thickness and copper options
Standard IM sheet offerings are 30 and 60 mil. Most property-table observations use a 60 mil laminate.
The IM construction uses a dedicated 35 µm ED cladding option. Retain the exact foil designation and test method.
Fabrication considerations
- Use a PTFE-capable fabricator and preserve foil orientation and handling cleanliness through manufacture. The antenna test vehicle should include representative joints and launches so that a low-PIM laminate result is not mistaken for proof of the finished feed network.
Application fit
- Low-PIM antenna feeds
- Base-station antenna panels
- Intermodulation-sensitive RF structures
Limits and substitution checks
- The IM sheet characterizes specific 30 and 60 mil constructions using two 43 dBm swept tones near 1900 MHz. Those conditions do not establish a universal PIM limit at every frequency. Non-contact roughness measurements also should not be mixed with differently defined surface metrics.