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How PCB Manufacturer prepares the PCB layer stack up and determines the values?

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tennythomas

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I sent my previous queries regarding the PCB layer stack up and thickness of core and prepreg. I got a common reply - the PCB Manufacturer will prepare the same.

How can the PCB Manufacturer prepare the PCB Layer stack up and determine the value of thickness of core and prepreg?

Is the forum for the PCB Manufacturer available?

I ask this bcoz I am planning to get a job in a PCB Manufacturing company. The interviewer MAY ASK me how to prepare the PCB Layer stack up and determine the value of thickness of core and prepreg?

Please guide me.

Thanks in advance.
 

PCB Manufacturer

common practice is PCB designer will suggest a layer stack up.but in most of the cases it will not be acceptable for fabricator.Fabricator will have some possible Core and prepeg thickness .
Some formula is there which relates characteristic impedence,distance from ground(referance) plane and trace width .here distance from referance plane is the major factor which controls the impedence.So by adjusting ( adjusting core and prepeg thickness)this you can achieve desirable impedence.
 

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Re: PCB Manufacturer

Hi Nikhil,

Can u show me a formula and an example?

Thanks....
 

PCB Manufacturer

Just download Appcad. It's free.

Keith
 

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Re: PCB Manufacturer

I use appcad for calculating impedance and dielectric thickness.

From the appcad (microstrip) window, what is the significance of L (physical length of a track), as it does not affect impedance?

Can I ignore L while calculating impedance and dielectric thickness?
 

PCB Manufacturer

The length doesn't matter when calculating impedance. Nor does frequency. They are used when you are wanting to make a quarter wave line, for example.

Keith
 

Re: PCB Manufacturer

Multilayer PCB consists of a layer of alternating cores and prepregs.

Please let me know whether the thicknesses of cores (alternating) / the thicknesses of prepregs (alternating) are same or mixed.
 

Re: PCB Manufacturer

tennythomas said:
Multilayer PCB consists of a layer of alternating cores and prepregs.

Please let me know whether the thicknesses of cores (alternating) / the thicknesses of prepregs (alternating) are same or mixed.
Click to expand...

Core build & prepreg build are the same. Core build are just partnered with 2 copper layer from top & bottom. If you cannot recommend a stack up to your manufacturer you can just put on your fabrication notes the impedance controlled lines.

example :

All 0.15 line width on top layer will be 50 ohms single line
All 0.1 line width on top layer will be 100 ohms differential line

Hope this helps.
 

Re: PCB Manufacturer

I heard that the thicknesses of cores (alternating) and prepregs (alternating) are same or different or mixed depending on the application.
 

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