The distinction between TMM 10 and TMM 10i includes dielectric behavior and isotropy, not a simple quality ranking. Evaluate how the fields in your circuit sample the material before selecting the input used by the solver.
Understand the isotropy question
The official TMM family identifies TMM 10i as an isotropic dielectric option. That matters when a structure contains significant fields in more than one direction. A scalar material input may be adequate for an initial study, but it can conceal directional behavior that becomes important in tightly coupled structures, transitions or three-dimensional fields. Confirm the relevant data before simplifying the model.
Compare the same electrical function
The names do not imply identical dielectric constants. Read the TMM 10 and TMM 10i records, then re-optimize widths, lengths and coupling distances separately. A design copied unchanged between them can move in frequency even if both are broadly described as high-Dk thermoset materials. Use source-specific design values and retain their measurement context.
Example: a coupled microwave component
Consider a compact coupler with narrow spacing and bends near its ports. Run a geometry study for each material and compare amplitude balance, phase balance, return loss and isolation across the required band. Include manufacturing variation in the gap and thickness. A candidate with a slightly larger optimized layout could be preferable if it offers a more robust result under achievable tolerances.
Resolve the mechanical and thermal details
Check the mounting arrangement, copper configuration and fabrication guidance for the exact construction. Measure the selected circuit through its operating-temperature range rather than inferring finished-circuit stability from one thermal coefficient. Where substitution into an established design is contemplated, retain a measured reference unit and require formal approval of the updated model and drawing. The qualification guide helps link each electrical or mechanical requirement to a repeatable acceptance measurement.
Ask whether the available material model represents a single direction or a full dielectric tensor, and record the answer. When evidence is insufficient for a complex field distribution, a dedicated resonator or coupled-line measurement is more informative than choosing whichever nominal Dk gives the preferred simulation.
Source-aware property comparison
TMM 10
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 9.20 ± 0.230 | 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 | 9.8 | Typical, 8–40 GHz; differential phase length method. Average across the common constructions in the cited datasheet. Source |
| Dissipation factor | 0.0022 | Typical; 10 GHz, Z direction; IPC-TM-650 2.5.5.5. Test temperature is not stated in this datasheet row. Source |
| Thermal conductivity | 0.76 W/(m·K) | Typical; 80°C, Z direction, ASTM C518; product datasheet thermal table. Source |
| CTE, X axis | 21 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Y axis | 21 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Z axis | 20 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 | -38 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 | 0.09 % | 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.
TMM 10i
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 9.80 ± 0.245 | 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 | 9.9 | 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 | 0.76 W/(m·K) | Typical; 80°C, Z direction, ASTM C518; product datasheet thermal table. Source |
| CTE, X axis | 19 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Y axis | 19 ppm/°C | Typical; 0°C to 140°C; ASTM E831 and IPC-TM-650 2.4.41, product datasheet. Source |
| CTE, Z axis | 20 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 (estimated) | -43 ppm/°C | Estimated, explicitly marked with an asterisk in the datasheet; -55°C to 125°C, IPC-TM-650 2.5.5.5. Frequency is not separately stated in this row. Source |
| Water absorption | 0.16 % | 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.
Choose with the relevant dielectric directions and re-optimized geometry, then verify the finished coupled structure.