FreeLists / si-list / [SI-LIST] Re: Impedance deviation due to prepreg shrinking

[steve weir <weirsi@xxxxxxxxxx>]

Cengiz, yes the material varies.  This is an issue that addresses the skill 
and experience of the board fabricator.  An experienced shop will be able 
to adjust the unpressed stack thickness and copper line width so that after 
pressing good impedance control is maintained when the stack-up is 
reasonable to begin with.

Steve.


At 12:28 PM 7/11/2005 +0000, caydin@xxxxxxxxxxxxxxxxx wrote:

>Dear listl,
>
>How prepreg layers effect the impedance of
>a stripline? To clarify, my stack-up is;
>
>S1
>--------------  core
>--------------
>GND
>--------------  prepreg
>--------------
>S2
>--------------  core
>--------------
>VDD1
>--------------  prepreg
>--------------
>S3
>--------------  core
>--------------
>GND
>--------------  prepreg
>--------------
>S4
>--------------  core
>--------------
>VDD2
>--------------  prepreg
>--------------
>GND
>--------------  core
>--------------
>S5
>
>We assume that pcb cores are hard enough to
>achieve the required line impedances.
>But, how about the impedances for the striplines
>with one core and one prepreg layer as neighbours,
>such as GND-S2-VDD1. Is there a rate of deviation after
>pcb manufacturing due to prepreg shrinking? Is not it
>more problematic if we have multiple core and
>prepreg layers?
>
>Any comments, suggestions? Thank you.
>
>Cengiz Aydin
>Researcher
>Bilkent University
>
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