Kappa 438 is a ceramic-filled hydrocarbon thermoset laminate reinforced with woven glass. It provides a controlled RF substrate with permittivity in the region often associated with conventional PCB materials, while retaining product-specific electrical characterization. Its Design Dk is documented at 2.5 GHz, which should not be silently relabeled as a 10 GHz observation.
Material system
Ceramic-filled hydrocarbon thermoset reinforced with woven glass
Technical properties
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 4.10 ± 0.08 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5 clamped stripline; direction is not separately recorded here. Source |
| Design dielectric constant | 4.38 | Typical; 2.5 GHz, differential phase length method; Z direction. Datasheet footnote 3 describes an average across common constructions. Source |
| Dissipation factor | 0.005 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5; direction is not separately recorded here. Source |
| Thermal conductivity | 0.64 W/(m·K) | Typical; ASTM D5470, 80°C, through-thickness direction. Source |
| Thermal coefficient of dielectric constant | -21 ppm/°C | Typical; -50°C to 150°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); 10 GHz. Source |
| Water absorption | 0.07 % | Typical; D24/23, IPC-TM-650 2.6.2.1. 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 when the intended circuit geometry and fabrication route fit a thermoset material of this dielectric range. Compare it with a named FR4 construction or Anteo using matched frequency and copper conditions.
- For a broadband line, verify the model across the required band. A single Design Dk at 2.5 GHz is a starting point, not evidence of exact broadband phase behavior for every geometry.
Thickness and copper options
The sheet lists 10, 20, 30, 40 and 60 mil standard offerings, with thicker configurations by enquiry.
ED copper is listed. Confirm the precise foil and any special low-profile option separately.
Fabrication considerations
- Define the core, foil and bonding stack with the fabricator and check the relevant RO4000-style process compatibility statements for the actual board. Include etch and finished-copper controls in an impedance drawing rather than relying only on a laminate name.
Application fit
- Controlled RF interconnects
- Thermoset microwave boards
- Material substitution studies
Limits and substitution checks
- The product sheet and selector differ in moisture-test presentation. Similarity to Anteo in some table entries is not proof of product equivalence, renaming or interchangeable supply. Do not infer a transition history without an explicit manufacturer notice and construction comparison.