TC350 and TC350 Plus should be compared as complete RF and thermal constructions. A thermal-conductivity number without its measurement method and direction cannot establish how much cooler an amplifier board will run.
Normalize the thermal evidence
Read the source attached to each conductivity observation for TC350 and TC350 Plus. Confirm direction, sample temperature and test method before calculating a ratio. If the conditions differ, retain the values separately and obtain comparable evidence. Do not silently select the larger of two published observations as the material’s definitive conductivity.
Identify the thermal bottleneck
Draw the route from the active device through its attachment, copper, dielectric or vias, bonding interface and heatsink. Determine which part is most responsible for the temperature rise. The thermal-resistance tool estimates a simple through-thickness slab; it does not include spreading, contact resistance or the package. A large improvement in one layer can have a small effect if another interface dominates.
Example: a high-power matching board
Suppose the transistor has a direct mechanical heat path into a baseplate while its matching lines sit on the laminate. Evaluate the temperature and loss of those lines separately from the junction-to-baseplate path. Measure gain, efficiency and return loss at the intended power and duty cycle. Material thermal behavior can interact with the matching circuit, so a thermal-only bench comparison is incomplete.
Keep fabrication and acceptance aligned
Confirm dielectric thickness, foil, drilling and bonding for both candidates. Compare the same mounting pressure, interface preparation, airflow and temperature reference in the prototype test. Record the electrical properties needed by the circuit model, including temperature dependence where relevant. Avoid interpreting the word Plus as proof of improvement in every property. Select the candidate that produces an adequate combined result under repeatable conditions, and retain the tested stackup as the approved build rather than permitting unrestricted substitutions.
Use the same definition of temperature rise for both samples. A case temperature, top-surface infrared reading and inferred junction temperature describe different locations and uncertainties. Document sensor location and measurement method so a change in instrumentation is not mistaken for a material improvement.
Source-aware property comparison
TC350
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 3.5 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5 clamped stripline; direction is not separately recorded here. Source |
| Dissipation factor | 0.002 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5; direction is not separately recorded here. Source |
| Thermal conductivity | 0.72 W/(m·K) | Typical, through thickness; ASTM D5470. The product table does not state test temperature. Source |
| Thermal coefficient of dielectric constant | -9 ppm/°C | Typical; -40°C to 150°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); 10 GHz. Source |
Typical reported values are not a purchase specification. Process Dk, design Dk and values measured at different frequencies are not interchangeable.
TC350 Plus
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 3.5 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5 clamped stripline; direction is not separately recorded here. Source |
| Design dielectric constant | 3.62 | Typical; 10 GHz, microstrip differential phase length method, C-24/23/50 conditioning. Source |
| Dissipation factor | 0.0017 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5; direction is not separately recorded here. Source |
| Thermal conductivity | 1.24 W/(m·K) | Typical, through thickness; ASTM D5470. The product table does not state test temperature. Source |
| CTE, X axis | 10 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 | 9 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 | 38 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 | -42 ppm/°C | Typical; 50°C to 150°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); 10 GHz. Source |
| Water absorption | 0.05 % | Typical; E1/105 + D48/50, IPC-TM-650 2.6.2.1. Source |
| Density | 2.22 g/cm³ | Typical; C-24/23/50, ASTM D792. Source |
Typical reported values are not a purchase specification. Process Dk, design Dk and values measured at different frequencies are not interchangeable.
Normalize conductivity methods and validate the full RF assembly under a controlled thermal load.