[SI-LIST] : RE: Power planes

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From: Doug Hopperstad (doug.hopperstad@qlogic.com)
Date: Tue May 01 2001 - 09:34:13 PDT


I am currently looking at the following stackup for a design and would like
some feedback:

1. ---- ---- Top layer (Very little routing) (2 oz)
2. --------- Ground (1 oz)
3. --------- Split Power (1 oz)
4. --------- Ground (0.5 oz)
5. ---- ---- Routing (0.5 oz)
6. ---- ---- Routing (0.5 oz)
7. --------- Ground (0.5 oz)
8. ---- ---- Routing (0.5 oz)
9. ---- ---- Routing (0.5 oz)
10. --------- Ground (0.5 oz)
11. ---- ---- Routing (0.5 oz)
12. ---- ---- Routing (0.5 oz)
13. --------- Ground (0.5 oz)
14. --------- Power - 3.3v (1 oz)
15. --------- Power - 2.5v (1 oz)
16. ---- ---- Bottom layer (Very little routing) (2 oz)

The dual-striplines are separated by grounds and the power-to-grounds are
adjacent to each other for high frequency noise coupling. The board will be
made from Getek with Er = 3.9 with a total thickness of 125 mils.

Dielectric spacing between layers:
1:2, 15:16 = 14 mils
2:3, 14:15 = 6 mils
3:4, 4:5, 6:7, 9:10, 10:11, 12:13, 13:14 = 4 mils
5:6, 8:9, 11:12 = 12 mils

Layers 14 and 15 are going to be dedicated power planes, each for a single
voltage source (2.5v and 3.3v). The split plane will have 1.35v, 1.8v and
5v.

1. Is there any concerns with making the outer layers 1 or 2 ounce compared
to the inner layers set at 0.5 ounce?
2. Put the split power plane between two grounds planes?
3. How much of a dielectric spacing would be best between two adjacent power
planes?

I am open to using layer 2 as a power plane instead of a ground. I look
forward to any comments on this issue, thanks.

Doug Hopperstad

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