1. Broadside coupled pair. On core / On prepreg ?

2. Broadside Coupled Pair - On Core? - On PrePreg?
In the current version of Si8000m impedance field solver we show broadside coupled pairs modeled only on the two sides of a core. This is the preferred construction as registration of the line pair is optimised. However…
In the event that the pair are modeled on the two sides of prepreg, it becomes necessary to adjust the H1 and H2 dimensions to take into account the fact that they no longer directly correspond to the thickness of the dielectric material layers. This shortcoming will be addressed in a future version of Si8000 but until that time the drawings on the following pages illustrate how the H1 and H2 dimensions must be constructed from the dielectric and copper dimensions.
The three pictures that follow “are worth a thousand words.”

3. Broadside Coupled PairH2 W2 T1 W1 H1 W1 T1 W2 H2

4. Broadside Coupled Pair on CoreH2
PrePreg Er2 W2 T1 W1 H1
Core Er1 W1 T1 W2 W2
PrePreg Er2 H2

5. Broadside Coupled Pair on PrePreg
Core Er2 H2 W2 T1 W1 H1
PrePreg Er1 W1 T1 W2 W2 H2
Core Er2
We “trick” the current structure into giving a close approximation of impedance.
H1 = overall prepreg thickness – (2x T1) and H2 = core thickness + T1.
We ignore the small error caused by the dielectric interface being in the wrong position for the field solver (the solver thinks it is at the H1 & H2 interface.)

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