Intel 820E manual Copper Tab Area Calculation

Intel® 820E Chipset

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Table 4. Copper Tab Area Calculation

Dielectric	Separation between	Min.	Air Gap	Compensating	Copper Tab	C-TAB
Thickness	Signal Trace and	Ground	between Signal	Capacitance	(C-TAB) Area	Shape
(D)	Copper Tab	Flood	and GND Flood	(pF)	(A) (sq. mils)	(mils)
4.5	6	10	6	0.65	2800	140 L x 20 W
						70 L x 40 W

Based on Equation 1, the tab area is 2800 sq. mils, where ε r 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 the copper area over the ground plane. The actual length and width of the tabs may differ as a result of routing constraints (e.g., if the tab must extend to center of hole, or antipad). However, each copper tab should have the equivalent area. For example, the copper tabs in Figure 21 have the following dimensions, when measured tangentially to the antipad:

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

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

Figures 21 through 25 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.

42 Design Guide