[SI-LIST] : 18 layer stackup question

About this list Date view Thread view Subject view Author view

From: e (evillaf@home.com)
Date: Wed Apr 12 2000 - 02:36:47 PDT


> I am currently in layout with an 18 layer board stacked up as follows:

1 - TOP
    3 mil
2 - GND
    5 mil
3 - IN1
    4 mil
4 - IN2
    5 mil
5 - GND
    2 mil (buried cap)
6 - 3.3V
    5 mil
7 - IN3
    4 mil
8 - IN4
    5 mil
9 - GND
    2 mil (buried cap)
10 - 5V
    5 mil
11 - IN5
    4 mil
12 - IN6
    5 mil
13 - GND
    2 mil (buried cap)
14 - 1.8V
    5 mil
15 - IN7
    4 mil
16 - IN8
    5 mil
17 - GND
    3 mil
18 - BOTTOM

All layers use 1 oz Cu except TOP and BOTTOM use 0.5 oz. I have specified minimum of 20 mil center-to-center distance between signal layers to minimize cross talk. This give a D/H ratio of 4, per
Howard Johnson's book. Is this overkill? Most signals are running between 66-100 MHz, with rise times of 1-3 ns. I believe Dr. Johnson provides an example where he set the D/H ratio to 5 minimum.

Does anyone have any comments on the stackup? Is there anything I should watch out for?

All inner signal layers are closer to each other (4 mil) than to their respective reference planes (5 mil). Will this cause any problems?

Thanks in advance.
Ellis

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Apr 20 2000 - 11:36:09 PDT