ENGINEERING ANSWER
RO4350B provides a defined RF material system, while FR-4 is a broad family with many electrical properties. Compare an exact FR-4 grade and construction rather than a single generic Dk or loss value.
What to decide before release
Evaluate line length, frequency, allowed loss and dimensional control. A short feed and a long distributed filter may reach different decisions. Include material availability and the supplier’s supported construction in the comparison.
Checks to put in your design brief
- Name the FR-4 grade
- Use matching test conditions
- Compare finished-board cost and performance
Important distinction
A fixed price multiplier between RO4350B and all FR-4 boards is not defensible without a common quotation scope.
Sources & basis
Material facts follow the cited source. Design checks are preliminary guidance, not supplier process instructions.