I only have experience with low-speed boards that are 4 layers at most. I want to get into full-speed USB 2.0 and 100Mb/s ethernet, so I need some impedance controlled traces. Instead of doing something professional first, I want to put together a hobby board that does these speeds.
Advanced circuits, the PCB house that I use, has this pdf about stackup thickness. I've spent about an hour googling, but I haven't come up with clear reputable results to the following questions related to stackup thickness:
- What is pre-preg? What is its purpose in manufacturing? I always thought that we just glued copper to an FR-4 sheet and then photoexposed it.
- Why does pre-preg thickness change depending on how much of the pcb is filled up?
- If I order an "impedance controlled" board, will the pre-preg thickness be better controlled? How is this process different than "regular" boards?
- Is there a textbook or nice, long app note that talks about all the nitty-gritty of pcb manufacture?