Subject: | |
From: | |
Reply To: | TechNet E-Mail Forum. |
Date: | Fri, 5 Feb 1999 10:04:53 -0800 |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
doug smith wrote:
>
> Scott,
> You need to specify which layers are planes and traces,
>
> Example:
> L1 s
> L2 p
> L3 s
>
> etc...
> Regards,
> Doug
>
> >>> Scott Decker <[log in to unmask]@yusa.com> 02/05 9:26 AM >>>
> Hi All
> I have a question / problem....
> I recently used the Impedance calculator on IPC WEB site and
> found a very interesting problem. On one occasion a few weeks
> ago, I used the calculator to do a quick stackup for a board I'm
> working on. The results were fine and were used as a baseline
> for the FAB shop to find me the values they use. I was just showing
> another designer here this neat calculator and changed the values
> I used to the values that the FAB shop gave me. Guess What....
> The calculator came back with an un-balanced impedance value!
> This is a very strange problem. I put in a balanced stackup
> and the values for impedance were different from the top to the
> bottom by 5 ohms. Sure you say, that's the 10% but, why are the
> numbers different? Maybe some of you out their can try these numbers.
> First. 6 Layer Board.
> .5 oz on both outside layers and 1 oz on all inside signals and planes.
> .005" traces on all layers
> Dielectric thickness as follows:
> 6.5
> 10
> 18
> 10
> 6.5
> Er value of 4.2
> OK now you have the numbers, the impedance should be around 72 ohms.
> But Wait! The values I got were 77 72 72 72...... What Gives?
>
> Any Comments???
> I already herd that it's because the UV rays from the sun were hitting
> the top of the board more, but I don't think that's true....(:-}
>
> --
> Scott Decker
> Senior PCB Designer
>
> AKA: PadMasterson
> E-Mail: [log in to unmask]
> -----------------------------------------------------------------
>
> ^
> ^^^ Praegitzer Design - A Division of Praegitzer Industries
> ^^^^^ 7245 N.W. Evergreen Pkwy, Suite 100, Hillsboro, OR 97124
> ^^^^^^^ Phone #: (503) 531-2050 Ext. 1820 Fax #: (503) 531-2051
> Check out our WEB site at http://www.pii.com
> -----------------------------------------------------------------
Doug,
I didn't' say it specifically, but the calculator on the site comes up
with the stackup I had and is the only one that can be used in this
case.
It should be:
S1
P1
S2
S3
P2
S1
Later
--
Scott Decker
Senior PCB Designer
AKA: PadMasterson
E-Mail: [log in to unmask]
-----------------------------------------------------------------
^
^^^ Praegitzer Design - A Division of Praegitzer Industries
^^^^^ 7245 N.W. Evergreen Pkwy, Suite 100, Hillsboro, OR 97124
^^^^^^^ Phone #: (503) 531-2050 Ext. 1820 Fax #: (503) 531-2051
Check out our WEB site at http://www.pii.com
-----------------------------------------------------------------
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
|
|