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

["Bleu Carlo Franco" <Carlo_Franco.Bleu@xxxxxxxxxx>]

Cengiz,
theoretically speaking, when you define the thickness of dielectric, =
prepreg or core, you ask to your customer for the value after the =
pressing phase. So you do not care if the dielectric is core or prepreg, =
it is your customer problem how much thick is the initial prepreg to =
obtanin the wanted final thickness.

Hope this help
Carlo

-----Messaggio originale-----
Da: steve weir [mailto:weirsi@xxxxxxxxxx]
Inviato: luned=EC 11 luglio 2005 11.35
A: caydin@xxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Oggetto: [SI-LIST] Re: Impedance deviation due to prepreg shrinking


Cengiz, yes the material varies.  This is an issue that addresses the =
skill=20
and experience of the board fabricator.  An experienced shop will be =
able=20
to adjust the unpressed stack thickness and copper line width so that =
after=20
pressing good impedance control is maintained when the stack-up is=20
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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