Layer Stackup and impedance

stack up and impedance

Hi,
How could a PCB designer determine the PCB stackup and Impedance
of the board if the customer or manufacturer didnot mention anything about it? Is there any standard stackup and impedance for the PCB board?
How much thickness should be set for each layer? core or prepeg
values should be in how much thickness?
What is meant by impedance control board?
Can ourselves give the trace width? How to determine the trace width as a PCB designer?

Thanks in advance.

Regards,
Devi.

layer stackup matched impedance

Hi,
First, the stack layer is decided depending on the type of your application. If you application is at low speed, not sensitive to noise, than you can use simple or double plated board. If you app is high frequency analog, digital or mixed, then the things will complicate. You have to use multilayer boards with ground and power planes. The mechanical details of the board (thickness for plating, dielectric, prepreg, min hole size, min track size, max number of layers), all these you should discuss with your pcb manufacturer, each manufacturer has its own limits. Most of the manufacturers who have a website will offer these informations on site. The trace width is important from two points of view. When the signal which pass a trace is low frequency but high current, the trace must be wide enough to withstand the current density. For high speed and rf signals, the trace width (along with other factors - dielectric constant, dielectric thickness, working frequency, and others) will determine the characteristic impedance of the track. In your post, I think you meant "imedance of a track" not "impedance of the board". It is important to use matched impedance transmission lines between diffrent parts of your design, in order to avoid signal reflections, which can affect the functionality of your design. You can find more informations on this forum, search at ebooks after "signal integrity" or "pcb rf design" or similar. A good tool to calculate the impedance of a track is appcad from agilent. It is free.

pcb layer stackup prepeg

The impedance of the routes is fixed by the width and thickness of the copper and the distance from a power plane. Get a program like HyperLynx, which will work out the impedance for you. You need a constant impedance route for high speed signals, a common value is 50 ohms. Any deviation from this will result in distortion and reflections. You need a manufacturer of your board that can do controlled impedance. This is only relevant to high speed design. The impedance also depends on which layer the track is on and the stack up, stripline or microstrip. Get HyperLynx!