When engineers search for standard FR4 thicknesses, they usually expect a simple answer. Instead, they often encounter conflicting information.
One source lists a 0.10 mm core. Another shows 0.136 mm. A third refers to a 1080 prepreg with a thickness of 0.075 mm, while a supplier datasheet lists an entirely different value.
The confusion arises because several different concepts are being mixed together:
Core thickness Finished core thickness Prepreg thickness Pressed dielectric thickness Glass style Resin content Lamination behaviour All of these values are related, but they are not the same thing.
Material selection for a PCB is rarely driven by electrical requirements alone. The operating environment — temperature, humidity, chemical exposure, thermal cycling — defines the boundary conditions within which the laminate must perform reliably over its service life. Choosing a material adequate for the bench but wrong for the field is one of the most consistent sources of premature failure in electronic assemblies.
The Four Laminate Families # For the purposes of environmental selection, the relevant laminate families are:
When buyers specify FR4 High-Tg on an RFQ, they often do so because a datasheet or engineer told them to. Fewer understand why it behaves differently from standard FR4 — and why that difference matters when a board heats up under load, goes through lead-free soldering, or operates in a demanding environment.
The answer lies not in the glass fibres or mineral fillers, but in the epoxy resin chemistry itself.