[SI-LIST] Re: PCB thin dielectrics
- From: "Qazi Iqbal" <qazi@xxxxxxxxxx>
- To: <wolfgang.maichen@xxxxxxxxxxxx>, "'Bowden, Ivor'" <ibowden@xxxxxxxxxxxxxxxxx>
- Date: Mon, 21 Dec 2009 16:38:37 -0700
Ivor,
Try to see if you can skip the adjacent planes for the signals to use as a
reference plane (return path). In many applications we create a void in the
adjacent planes and then use the next plane (above or below it) as the
reference plane. That way you can avoid having very thin traces for the
controlled environment.
-Qazi
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of wolfgang.maichen@xxxxxxxxxxxx
Sent: Monday, December 21, 2009 4:26 PM
To: Bowden, Ivor
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: PCB thin dielectrics
Ivor,
it depends what signals you have. If they are slow-speed (= slow rise
times!), i.e. no need to use impedance-controlled transmission lines,
there is no signal-integrity(!) reason to not use them.
For high-speed signals just run a few numbers. A stripline sandwiched
between two 1 mil layers of eps_r=4 would need to have a width of around 1
mil to achieve 50 Ohm impedance (neglecting trace thickness - traces of
finite thickness will make the situation even worse). That is not
manufacturable with normal processes, and even if it were, you etch
tolerances will kill you. Second, keep in mind the copper has some
thickness, too - 1 oz copper is about 1.4 mils. How can you ever achieve
conformal embedding in a dielectric that is thinner than the trace? (you
can't).
The signal-integrity tradeoffs of thin traces are straightforward - high
skin loss, poor impedance control.
Wolfgang
"Bowden, Ivor" <ibowden@xxxxxxxxxxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
12/21/2009 03:11 PM
To
<si-list@xxxxxxxxxxxxx>
cc
Subject
[SI-LIST] Re: PCB thin dielectrics
I would like to thank everyone that responded, both on and off the list.
While thin dielectric for power planes have advantages, can it be used for
signal layers? To maintain impedance, signal traces have to be reduced to
impractical levels or permittivity must be increased. How common is this
in practice, what are the tradeoffs?
Ivor
_______________________________________________________________________
This e-mail and any files transmitted with it are proprietary and intended
solely for the use of the individual or entity to whom they are addressed.
If you have reason to believe that you have received this e-mail in error,
please notify the sender and destroy this email and any attached files.
Please note that any views or opinions presented in this e-mail are solely
those of the author and do not necessarily represent those of the
Curtiss-Wright Corporation or any of its subsidiaries. Documents attached
hereto may contain technology subject to government export regulations.
Recipient is solely responsible for ensuring that any re-export, transfer
or disclosure of this information is in accordance with applicable
government export regulations. The recipient should check this e-mail and
any attachments for the presence of viruses. Curtiss-Wright Corporation
and its subsidiaries accept no liability for any damage caused by any
virus transmitted by this e-mail.
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
