TMM 4 provides a midrange dielectric constant in the ceramic-filled thermoset TMM family. It is a candidate when a designer wants more compact RF structures than lower-Dk materials allow while retaining a rigid, machinable microwave substrate. Its temperature coefficient is comparatively small and positive within the published TMM table.
Material system
Ceramic-filled thermoset polymer
Technical properties
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 4.50 ± 0.045 | 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 | 4.7 | 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 | 16 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Y axis | 16 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Z axis | 21 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 | 15 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 | 0.07 % | 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
- Use it to explore compact feed and matching geometries without jumping directly to the high-Dk TMM grades. Compare actual line width, coupling and footprint using the Design Dk observation rather than the material's numerical name.
- For a temperature-sensitive circuit, include both dielectric change and mechanical expansion. A small material coefficient is helpful evidence, but is not a complete prediction of resonant-frequency or phase stability.
Thickness and copper options
Choose a documented TMM thickness and tolerance; mounting flatness and dielectric spacing may impose different requirements.
Specify copper weight and treatment. Special cladding availability needs supplier confirmation.
Fabrication considerations
- Ask the fabricator to review the chosen thickness, drill sizes and machining support for a ceramic-filled thermoset. Define copper and mechanical tolerances on the same drawing so that RF and mounting requirements do not conflict late in the build.
Application fit
- Microwave feeds
- Compact RF networks
- Precision substrate components
Limits and substitution checks
- TMM 4 is not FR4 and the number four does not indicate a universal FR4 replacement. It is also not a flame-retardant grade in the selector. Qualification should be based on the actual electrical, mechanical and environmental requirements of the assembled circuit.