ENGINEERING ANSWER
Hybrid construction can reserve RF material for critical fields while using another laminate elsewhere. Whether it lowers total cost depends on processing, bonding, yield and material procurement, not just the price of the core.
What to decide before release
Ask the supplier for a construction it already supports. Confirm dielectric properties at every critical field region and check thermal/mechanical compatibility. A signal that changes layers may move into a different dielectric environment.
Checks to put in your design brief
- Keep critical fields in characterized materials
- Specify all bonding layers
- Compare total fabricated cost
Important distinction
Do not assume every FR-4 prepreg can be substituted into a qualified RF hybrid.
Sources & basis
Material facts follow the cited source. Design checks are preliminary guidance, not supplier process instructions.