What are the parameters to be look up for selection of stack up for a new designing, could anyone guide us in step by step manner. It would be very helpful for us.
This higly depends in your application requirements and your manufacturer. Do I suggest you detail what you got so far and at which step you hang right now.
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calculating of impedance and track width
This is out of scope of KiCad, at least currently. Maybe someone can give you a link, but you should find a forum for general electronics.
You can search for e.g. “high speed pcb design”.
Normally I first try to pick the layer count (based on routing complexity) and the board thickness (based on mechanical constraints). After that, I can either look up a standard stackup given those parameters (many manufacturers publish these), or if I already have a relationship with a fabricator, I can email them the custom requirements and they will tell me what stackup to use.
With controlled impedance, there are two ways to go:
For prototypes or lowest cost, you take the standard stackup of your manufacturer and plug it into a calculator (like the PCB Calculator built in to KiCad for example, or Saturn PCB Toolkit if you are ok with a closed-source tool that currently has many more features). This way you can figure the required width (and spacing, for differential pairs) from the given stackup for any impedance you need.
If this comes out to a reasonable number, you are good. If it comes out unreasonable (i.e. to achieve a given impedance your traces would need to be very wide or very narrow), probably it means your stackup (and in particular, the distance from your controlled-impedance routing layer to your reference plane layer) is wrong.
Then you have two options: First, you could choose a different stackup that has different reference plane distances, from the catalog of standard stackups available. This sometimes means choosing a board thickness other than the standard 1.6mm, which can be an easy/cheap way to get better stackups for a particular controlled impedance if the thickness doesn’t matter much to your design.
Second, if you can’t find something standard that works, your only resort is to contact a manufacturer and tell them about your constraints (thickness, layer count, routing vs. plane layers, what impedances you need and on which layers with which reference planes, etc). They can design a custom stackup for you. Of course, this is mostly only an approach for use in a professional setting as it will be much more expensive than the standard prototyping services.
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Thank you Craftyjon for helping me
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