Re: [SI-LIST] : bypass cap question (long, simple)

Christopher Donham (donham@axon.engr.sgi.com)
Mon, 2 Feb 1998 15:26:06 -0800 (PST)

> You could also reduce the end cost of the board by reducing the
> number of layers to 7 instead of 8 by using a split power plane. Thus
> your stackup could look like this:
>
> 1 Horizontal
> 2 V33 Plane/V5 Plane
> 3 GND Plane
> 4 Vertical
> 5 Horizontal
> 6 GND Plane
> 7 Vertical

Hmmm -- I thought that boards had to be created from layer pairs
I didn't know that a 7 layer could be easily constructed, and hence
cost less than an 8 layer board. (I am a novice at these things --
please correct me if I am wrong. I thought a board was constructed
by etching metal on either side of a "core" and then pressing it
together with "prepreg" in between. This would suggest an even
number of layers).

I also thought that to keep a board from warping, you wanted a
stackup that was symmetrical. So having planes 2 and 3 towards
the top and only plane 6 towards the bottom was also a cause for
concern. How big does a board have to be for this to be a concern?

Thanks (a lurker).

Chris

-- 
Christopher Donham
Silicon Graphics, VSG                             Phone:  (415) 933-2474
2011 N. Shoreline Blvd MS 43U-993                 FAX:    (415) 932-2474
Mountain View, CA 94043-1389                      E-Mail: donham@sgi.com