Hi Brad,

thanks for your informative email.  I figured asymmetry might be a bad 
thing, and it turns out i don't need to board to be exactly .063".  i am 
waiting to hear back from the fabricator as to the thicknesses of core and 
prepreg they stock.

thanks again for taking the time to provide me with some useful information.

-rimas

At 05:44 PM 8/1/2002 -0700, you wrote:
>Rimas,
>         have just a few minutes here to type out a reply, here are my brief
>comments.
>
>Your stackup is assymetrical. Your laminate top and bottom should be equal.
>An assymmetrical stackup will usually result in unacceptable bow & twist.
>Your bottom laminate thickness should match the top 6.3 mil thickness.
>
>Secondly, I would be pretty sure that you can't get core/prepreg in those
>precise thicknesses. I don't deal with this a lot but I would be suspicious
>about your xx.x mil thicknesses. Have you asked the fabricator what
>core/prepreg thicknesses they stock? Use their standard cores/prepregs to
>determine the best stackups, then calculate the impedance control trace
>widths that you would use/need for your particular impedance.
>
>Third, in your stackup you did not account for copper thickness for your
>total stackup thickness. 1/2 oz. CU = 0.7 mil 1 oz. Cu = 1.4mil 2 oz. Cu =
>2.8mil.
>
>         Is the thickness of your PCB that critical? Could you get away with
>0.055", 0.065", 0.050" or something inbetween. Just asking because that
>would give you more leeway in prepreg and core thickness selection.
>
>         Got to run right now. Chat with your fabricator to make sure your
>core/prepreg thickness is OK and that they believe your stackup is OK to
>fab. Doesn't matter what stackup you create if the fabricator doesn't have
>those prepregs or cores to build it with.
>
>Sincerely,
>Brad Velander.
>
>Lead PCB Designer
>Norsat International Inc.
>Microwave Products
>Tel   (604) 292-9089 (direct line)
>Fax  (604) 292-9010
>email: [EMAIL PROTECTED]
>http://www.norsat.com
>
>
>-----Original Message-----
>From: rimas [mailto:[EMAIL PROTECTED]]
>Sent: Thursday, August 01, 2002 4:06 PM
>To: Protel EDA Forum
>Subject: [PEDA] question about layer stackup/controlled impedance
>traces...
>
>
>hello out there,
>
>i'm about to have my first PCB design involving controlled impedance traces
>manufactured in the near future (just a small run of protos).  I only have
>controlled impedance traces on the top layer.  using the transmission line
>impedance calculation tool at:
>
>http://www.eskimo.com/~ultra/calc.htm
>
>(which someone on this list pointed me to before, thanks!)
>
>i've discovered that if I'm using FR4 and 7 mil traces with 2oz of copper,
>that a dielectric width of 6.3 mils will give me a reasonably close
>impedance (52.6 ohms and i'm aiming to get 50)
>
>now here's my question - is this a reasonable way to do the layer stackup?
>(oh yeah, this is a 6 layer board and i'd like the resulting board to be
>.063" wide)
>
>(TOP)
>core -> 6.3 mils
>prepreg -> 12.6 mils
>core -> 12.6 mils
>prepreg -> 12.6 mils
>core ->  18.9 mils
>(BOTTOM)
>
>this seems logical to me but being as that i am inexperienced and such
>things and have noone knowledgeable around here to ask i thought i would
>ask for this group's wisdom.  thanks for any help, hope the
>non-directly-protel related question doesn't bother anyone.
>
>-rimas
>
>
>************************************************************************
>* Tracking #: A050A66B34F2154BAF06DE47FD1ACB3A65DE569F
>*
>************************************************************************


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/leave.html
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Forum Guidelines Rules:
* http://www.techservinc.com/protelusers/forumrules.html
*
* Browse or Search previous postings:
* http://www.mail-archive.com/proteledaforum@techservinc.com
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Reply via email to