Re: [SI-LIST] : BackPlane stackup

Chris Heard/US/3Com (Chris_Heard/US/3Com%3COM@SMTP1.isd.3com.com)
29 Jul 97 9:16:14 EDT

Your proposed stackup is not symmetrical about the neutral axis of the pcb, and
at a thickness of only 93 mils, the board will likely warp.

You may want to address why 88 ohms is needed, seems incredibly high.

Chris Heard
3Com Corp

----- Previous Message ----------------------------------------------------

To: si-list @ silab.Eng.Sun.COM @ SMTP1
cc:
From: LinJohn @ mail.dec.com (John Lin - TAO) @ SMTP1
Date: Tuesday July 29, 1997 10:52 AM
Subject: [SI-LIST] : BackPlane stackup
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Hi,

Can somebody tell me about if it is feasible to have the
stackup configuration, as following, for a backplane design ?

---------------------------------Ground plane
1
35 mils
----------------------------------Signal
2
35 mils
-----------------------------------Ground Plane
3
15 mils
----------------------------------- Signal
4
The total thickness is 93 mils.

Doing so is to match the impedance of microstrip( layer 4) to
Stripline (layer 2) impedance to the value of 88 ohms.

I am afraid that the manufacturing cost will increase greatly
compared to the following.

---------------------------------- Ground
Plane
27 mils
---------------------------------- Signal
33 mils
---------------------------------- Signal
27 mils
----------------------------------- Ground
Plane

The total thickness is 93 mils.

Thanks in advance,

JOHNLIN
CAE Engineer of EDA Department
Digital Equipment Corp. Taiwan Branch
Email: Linjohn@mail.dec.com
TEL: 1-886-3-3900000 ext. 2565