CLTE materials use ceramic-filled PTFE with woven-glass reinforcement. Their selection context is dimensional and electrical stability in structures where registration, phase or plated-hole behavior must remain controlled through changing temperatures.
Begin with the stability requirement
A feed network needs stable electrical length; a multilayer assembly also needs layers and plated holes to tolerate thermal movement. List these separately. Low expansion does not by itself prove a phase limit because dielectric variation and physical length both contribute. Compare CLTE-AT, CLTE-XT, CLTE-MW and the base grade against the actual stackup.
Thin layers need construction-specific data
Do not average property records from different thicknesses or copper types into a single convenient Dk. For a thin RF layer, small changes in spacing and copper interface can alter the modeled response. Confirm the material direction used by the field solver and the fabrication drawing, especially where routing turns through multiple orientations.
Qualify the combined stack
Review bonding compatibility, registration allowance, drill strategy and the number of thermal processing cycles. A useful prototype includes a phase-sensitive line and a representative plated-hole structure. Measure before and after the agreed thermal exposure, with a defined recovery condition. The CLTE-AT versus CLTE-XT comparison provides a focused way to structure the decision.
References in this family
Select CLTE using an explicit electrical-stability target and the reliability demands of the complete multilayer stack.