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Chapter 20.
Stack-Ups
20.1
Reference Design Stack-ups
This section details the reference design stack-ups.
20.1.1
Importance of Stack-up Definition
Stack-ups define the number and order of board layers. Stack-up definition is critical to the
following design:
Circuit routability
Signal quality
Cost
20.1.2
Impact of Stack-up Definition on Design
Stack-Up Impact on Circuit Routability
If there are insufficient layers to maintain proper signal spacing, prevent discontinuities in
reference planes, obstruct flow of sufficient current, or avoid extra vias, circuit routing can
become unnecessarily complex. Layer count must be minimally appropriate for the circuit.
Stack-Up Impact on Signal Quality
Both layer count and layer order impact signal integrity. Proper inter-signal spacing must
be achievable. Via count for critical signals must be minimized. Current commensurate
with the performance of the board must be carried. Critical signals must be adjacent to
major and minor reference planes and adhere to proximity constraints with respect to
those planes. The recommended NVIDIA stack-ups achieve these requirements for the
signal speeds supported by the board.
Stack-Up Impact on Cost
While defining extra layers can facilitate excellent signal integrity, current handling
capability and routability, extra layers can impede the goal of hitting cost targets. The art of
stack-up definition is achieving all technical and reliability circuit requirements in a cost-
efficient manner. The recommended NVIDIA stack-ups achieve these requirements with
efficient use of board layers.
