TMM 3 is a ceramic-filled thermoset microwave material at the lower-permittivity end of the TMM family. It is useful where mechanical rigidity and stable processing are important alongside controlled RF properties. Its construction differs from both PTFE laminates and woven-glass hydrocarbon circuit boards.
Material system
Ceramic-filled thermoset polymer
Technical properties
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 3.27 ± 0.032 | Typical; 10 GHz, Z direction; IPC-TM-650 2.5.5.5. Test temperature is not stated in this datasheet row. Source |
| Design dielectric constant | 3.45 | Typical, 8–40 GHz; differential phase length method. Average across the common constructions in the cited datasheet. Source |
| Dissipation factor | 0.002 | Typical; 10 GHz, Z direction; IPC-TM-650 2.5.5.5. Test temperature is not stated in this datasheet row. Source |
| Thermal conductivity | 0.7 W/(m·K) | Typical; 80°C, Z direction, ASTM C518; product datasheet thermal table. Source |
| CTE, X axis | 15 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Y axis | 15 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Z axis | 23 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| Thermal coefficient of dielectric constant | 37 ppm/°C | Typical; -55°C to 125°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); frequency not separately stated in this datasheet row. Source |
| Water absorption | 0.06 % | Typical; D24/23, 0.050 inch (1.27 mm) specimen, ASTM D570; product datasheet, not the selector's different moisture conditions. 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
- Compare it with RO4003C when considering a rigid microwave substrate, but use the complete mechanical and manufacturing requirements rather than process Dk alone. The materials can produce different trace widths, thermal behavior and machining results.
- For a precision matching network, examine the effect of core-thickness tolerance and copper geometry on impedance. The low decimal uncertainty in a dielectric table does not remove those other sources of error.
Thickness and copper options
The TMM sheet offers several standard thicknesses; specify grade and thickness together rather than assuming every option is universal.
ED copper is listed, with alternative constructions by enquiry. Copper peel and routing support matter for small features.
Fabrication considerations
- Review cutting, drilling and support methods with a fabricator experienced in ceramic-filled thermosets. The absence of a PTFE matrix does not mean that every glass-epoxy tooling setting or handling practice is optimal for TMM.
Application fit
- Microwave matching circuits
- Rigid RF substrates
- Distributed components
Limits and substitution checks
- The selector identifies TMM grades as non-flame-retardant. TMM 3 also has a positive dielectric temperature coefficient; evaluate physical expansion and dielectric drift together for phase-sensitive circuits. A rigid microwave material is not automatically appropriate for flexing or tightly formed structures.