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About thick metal expansion

Question asked by DEPAOLA on Sep 26, 2006
Latest reply on Sep 26, 2006 by ALEPEREZ

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Hi All,
when using the thick metal expansion in momentum, the thickness of the dielectric layers in between each metal strip is increased only where there is some metal or is uniformly increased for all the layout? More explictly, if I have places where many metal layers overlap and places where there is only the top metal, is it correct to assume that the substrate is thicker even beneath the top metal?
Thanks a lot

Francesco

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ALEPEREZ Sep 26, 2006 3:07 AM
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The dielectric beneath (DOWN) or above (UP) the metal layer grows by the thickness specified for the metal. If metal exists, there is no dielectric in that volume, and if no metal exists, you have a thicker dielectric than specified in the substrate properties tab.
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DEPAOLA Sep 26, 2006 8:36 PM
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And what about the case when a thick metal is specified in the layer stack but not used in the layout? is the dielectric expanded anyway?
thanks
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ALEPEREZ Sep 26, 2006 10:09 PM
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Yes, because the substrate computation is performed before any layout is drawn. The *potential* Green's function coupling between srip/via layers wrapped around the added dielectric layer(s) is precomputed. If you later do not use those Green's functions, no problem.
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DEPAOLA Sep 26, 2006 10:25 PM
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One last question: in my case I have 9 thick metal layers with vias in between.Is it normal that meshing requires a lot of time?
thanks
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ALEPEREZ Sep 26, 2006 11:02 PM
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That depends on how well the metal is drawn, how many slivery overhangs may exist, and the overall size of the structure. 9 thick layers is generally considered a very complex stack up for the mesher and simulator.
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