Intel 440GX manual Motherboard Layout and Routing Guidelines

Motherboard Layout and Routing Guidelines

Figure 2-6. Six Layer Board Stack-up With 3 Signal Planes and 3 Power Planes

Z = 60 ohms				Primary Signal Layer (1/2 oz. cu.)
	5 mils	PREPREG
				Ground Plane (1 oz. cu.)
	18 mils		CORE
Z = 59 ohms				Inner Layer #1 (1 oz. cu.)

	8 mils	PREPREG
				Power Plane #1 (1 oz. cu)
	18 mils		CORE
				Power Plane #2 (1 oz. cu)
	5 mils	PREPREG
Z = 60 ohms				Secondary Signal Layer (1/2 oz. cu)

Total board thickness = 62.4

Additional guidelines on board buildup, placement and layout include:

•For a 4-layer single processor design, double ended termination is recommended for GTL+ signals. One termination resistor is present on the processor substrate, and the other termination resistor is needed on the motherboard. It may be possible to use single-ended termination, if the trace lengths can tightly be controlled to 1.5” minimum and 4.0” maximum.

•For a 6-layer dual processor design, no termination is required on the motherboard for GTL+ signals, as each end of the GTL+ bus is terminated on each processor. If a single Slot 1 is populated in a DP design, the second Slot 1 must be populated with a termination card.

•The termination resistors on the GTL+ bus should be 56 ohms.

•The board impedance (Z) should be between 50 and 80 ohms (65 ohms ±20%)

•FR-4 material should be used for the board fabrication.

•The ground plane should not be split on the ground plane layer. If a signal must be routed for a short distance on a power plane, then it should be routed on a VCC plane, not the ground plane.

•Keep vias for decoupling capacitors as close to the capacitor pads as possible.

2.3Routing Guidelines

This section lists guidelines to be followed when routing the signal traces for the board design. The order of which signals are routed first and last will vary from designer to designer. Some designers prefer routing all of the clock signals first, while others prefer routing all of the high speed bus signals first. Either order can be used, as long as the guidelines listed here are followed. If the guidelines listed here are not followed, it is very important that your design is simulated, especially on the GTL+ signals. Even when the guidelines are followed, it is still a good idea to simulate as many signals as possible for proper signal integrity, flight time and cross talk.

Intel®440GX AGPset Design Guide 2-5