Stack up means the PCB material configuration. For a typical 4-layer PCB, there are 2 prepeg and 1 core FR4 material. PCB trace impedance depends on the prepeg thickness. So, you much choose a suitable stack up and then do microstrip impedance calculation to ensure you get the correct impedance.
Core & Prepeg are FR4 materials inside a multilayer PCB.
Refer to above picture, the middle FR4 is the core. There are 2 #2116 prepeg FR4. One between L1 and L2. One between L3 and L4. There are several common type of prepegs. When you design a RF board, you need to know:
1. Total thickness of the board. E.g. 1.6mm? 1.0mm? or 0.8mm?
2. You need to define the stack up structure. E.g. what core thickness? What prepeg? copper layer thickness? You must discuss this with your PCB supplier.
All RF tracks running on top layer (i.e. L1) are microstrips. You can calculate the impedance with some online tools.
One simple tools is here:
http://www.cepd.com/calculators/microstrip.htm
I have a very powerful CAD which can simulate all type of microstrips, striplines, coplanar strips, ...
发表于 2013-10-17 23:44:46
