ENGINEERING ANSWER
The cited typical X, Y and Z coefficients of thermal expansion are 10, 12 and 32 ppm/°C. Direction matters: in-plane expansion affects registration, while through-thickness expansion contributes to stress in plated holes.
What to decide before release
Review expansion with layer symmetry, copper distribution, hole structure and thermal cycling. A hybrid board combines materials and bonding layers with different behavior; quoting the RO4350B core alone does not describe the assembly.
Checks to put in your design brief
- Identify axes in material data
- Review via aspect ratios with the fabricator
- Define relevant thermal-cycle testing
Important distinction
CTE alone cannot predict plated-hole lifetime. Copper quality, hole geometry, process control and assembly history also matter.
Sources & basis
Material facts follow the cited source. Design checks are preliminary guidance, not supplier process instructions.