Alternate Stack Ups - Intel 852GM Design Manual

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3.2.

Alternate Stack Ups

OEMs may choose to use different stack-ups (number of layers, thickness, trace width, etc.) from the
one example outlined in Figure 2. However, the following key elements should be observed:
1. Final post lamination, post etching, and post plating dimensions should be used for electrical
model extractions.
2. Power plane layers should be 1 oz thick and signal layers should be ½ oz thick. External layers
become 1 – 1.5 oz (1.2 – 2 mils) thick after plating.
3. All high-speed signals should reference solid ground planes through the length of their routing
and should not cross plane splits. To guarantee this, both planes surrounding strip-lines should be
GND.
4. Intel recommends that high-speed signal routing be done on internal, strip-line layers.
5. For high-speed signals transitioning between layers next to the component, the signal pins should
be accounted for by the GND stitching vias that would stitch all the GND plane layers in that area
of the motherboard. Due to the arrangement of the Processor and 852GM GMCH pin-maps, GND
vias placed near all GND lands will also be very close to high-speed signals that may be
transitioning to an internal layer. Thus, no additional ground stitching vias (besides the GND pin
vias) are required in the immediate vicinity of the Processor and 852GM GMCH packages to
accompany the signal transitions from the component side into an internal layer.
6. High-speed routing on external layers should be minimized in order to avoid EMI. Routing on
external layers also introduces different delays compared to internal layers. This makes it
extremely difficult to do length matching if some routing is done on both internal and external
layers.
7. If Intel's recommended stackup guidelines are not implemented, then the OEM is liable for all
aspects of their board design and simulations should be performed based on OEM stackup (i.e.
understanding impacts of SI and power distribution).
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Intel 852GM Chipset Platform Design Guide
General Design Considerations
29