The central reason to investigate RO4835 alongside RO4350B is long-term behavior in an oxidative thermal environment. Similar initial electrical data do not answer whether a specific circuit remains within its limits over its intended service life.
Define the exposure before comparing
Record continuous and peak temperatures, dwell times, oxygen exposure, protective coating and the amount of exposed dielectric in the layout. Material aging depends on the physical circuit and environment. An enclosure temperature alone may not describe the temperature near a power device. Do not turn a manufacturer comparison into an unconditional lifetime multiplier for a completed PCB.
Separate initial performance from drift
Compare RO4350B and RO4835 at equivalent thickness and copper configuration. Rogers positions RO4835 for improved oxidation resistance, but the initial impedance, loss and phase still require a valid model. A candidate that reduces aging concerns can still require dimensional or assembly changes. Preserve the exact source revisions used for the decision.
Example: an outdoor RF module
Consider a module whose narrowband response has little room for frequency drift. Build a baseline sample and candidate sample, measure the initial response, and expose them to an engineering-approved aging condition. Repeat measurements using the same temperature and recovery procedure. Compare resonance or phase drift, insertion loss and physical condition. This is a proposed evaluation approach; the site has not performed an aging test on either material.
Make qualification relevant to service
An accelerated test should have a defensible relationship to the failure mechanism you are investigating. A convenient oven exposure is not automatically a lifetime prediction. Agree acceptance limits and sample selection before testing, and include the bonding system, coating and finish used in production. Review the qualification workflow and seek material-specific guidance where the expected environment falls outside available evidence. If ordinary conditions already meet the requirement, a material change needs a clear benefit to justify requalification.
Inspect the places where dielectric is exposed around patterned copper and board edges when defining the aging sample. A fully clad reference coupon and an etched RF structure can present different exposure conditions, so choose the vehicle for the failure mechanism being investigated.
Source-aware property comparison
RO4350B
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 3.48 ± 0.05 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5 clamped stripline; thickness direction. Source |
| Design dielectric constant | 3.66 | Typical, 8–40 GHz; differential phase length method. Average across the common constructions in the cited datasheet. Source |
| Dissipation factor | 0.0037 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5; thickness direction. Source |
| Thermal conductivity | 0.69 W/(m·K) | Typical; ASTM C518, 80°C; through-thickness thermal conduction. 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 | 12 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 | 32 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 | 50 ppm/°C | Typical; -50°C to 150°C, IPC-TM-650 2.5.5.5 (modified temperature measurement); 10 GHz. Source |
| Water absorption | 0.06 % | Typical; 48 h at 50°C, 60 mil specimen, ASTM D570. Source |
| Density | 1.86 g/cm³ | Typical; 23°C, ASTM D792. Source |
Typical reported values are not a purchase specification. Process Dk, design Dk and values measured at different frequencies are not interchangeable.
RO4835
| Property | Reported value | Conditions / source |
|---|---|---|
| Process dielectric constant | 3.48 ± 0.05 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5 clamped stripline; thickness direction. Source |
| Design dielectric constant | 3.66 | Typical, 8–40 GHz; differential phase length method. Average across the common constructions in the cited datasheet. Source |
| Dissipation factor | 0.0037 | Typical, 10 GHz, 23°C; IPC-TM-650 2.5.5.5; thickness direction. Source |
| Thermal conductivity | 0.66 W/(m·K) | Typical; ASTM C518, 80°C; through-thickness thermal conduction. Source |
Typical reported values are not a purchase specification. Process Dk, design Dk and values measured at different frequencies are not interchangeable.
Evaluate RO4835 for a defined aging risk and validate drift on the actual circuit construction.