User's Manual

Intel

820 Chipset Design Guide 2-15

Layout/Routing Guidelines

Based on Equation 1, the tab area is 2800 sq mils, where ε

is 4.2 and D is 4.5. These values are

based on 2116 prepreg material.

Note that more than one copper tab shape may be used. The tab dimensions are based on copper

area over the ground plane. The actual length and width of the tabs may be different due to routing

constraints (e.g., if tab must extend to center of hole, or antipad); however, each copper tab should

have equivalent area. For example, the copper tabs in Figure 2-17 have the following dimensions,

when measured tangent to the antipad:

Inner C-TAB = 140 (length) x 20(width)

Outer C-TAB = 70 (length) x 40 (width)

The following figures show a routing example of tab compensation capacitors. Note that ground

floods around the RIMM pins must not be interrupted by the capacitor tabs, and they must be

connected to avoid discontinuity in the ground plane as shown.

Table 2-3. Copper Tab Area Calculation

Dielectric

Thickness

(D)

Separation

Between

Signal Trace &

Copper Tab

Minimum

Ground

flood

Air Gap

between

Signal &

GND Flood

Compen-

sating

Capacitance

in pF

Copper Tab

(C-TAB)

Area (A) In

sq mils

C-TAB

Shape

(mils)

4.5 6 10 6 0.65 2800

140 L x 20 W

70 L x 40 W