Layer stackup

What are the things to be included in layer stack up?

A stack is important when have controlled resistance traces like : Stripline and microstrip.
It includes the number of layers , the distance between layers ,FR4 and the copper height . The distance between layer is in MILS or MM. The copper is mostly in Um.
See the example. It is a mix of MM and Mils.

As I said , it's important when you have control impedance. In the stripline and Microstrip calculations the copper units is in OZ (1.4mil) .See attached calculators

When I design a stackup I usually ask these questions:

* How many routing layers do I need? How many plane layers are required? The sum gives you the total layers you need. If you get an odd number add an additional layer. PCBs generally have even number of layers.
* Is there a board thickness requirement?
* Which routing layers need to be referenced to which planes? This will help determine the order of planes.
* What impedance do you need for each routing layer? I then use an "impedance calculator":http://www.eeweb.com/toolbox/microstrip-impedance to help determine the trace width and distance between layers.

To add a bit to what's already been said, the stackup needs to include the material specification. A common board can be done with the default FR4, but if there are special requirements, then there are dozens of different PCB laminate materials available (aside from the copper), so you may have to discuss your specific needs with the PCB fabricator. Some of the things to consider: Is the material RoHS qualified? The thermal characteristics (Tg and Td parameters; higher temperature-resistant materials are usually required for lead-free soldering). The dielectric constant must be specified if your board is impedance-controlled.

For PCB layer stackup ,I find 2 blog, On this subject have detailed description.

"The impact of HDI and microvias on PCB design()":http://www.techdesignforums.com/practice/technique/density-revisited/

"PCB Stack-Up Design()":http://support.nexpcb.com/hc/en-us/articles/201138205-PCB-Stack-Up-Design-