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Reply To: | TechNet E-Mail Forum. |
Date: | Mon, 9 Mar 1998 18:15:43 -0500 |
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Hello all, an odd question that has come up in some evaluations:
I have a "known good" impedance calculator formula from IPC-2141 that has worked for years on Polyclad 226 material.
I know my circuit widths, dielectrics, stackup and coupon design are good.
THE DIFFERENCE tried Polyclad 370 material Higher Tg (170 vs 140)
DK/Er (4.5 on both)
THE PROBLEM - my formula says 48-52 ohms
coupons read on 2 different TDRs at 59-63 ohms
One has a Tr @ 30ps the other is newer so probably a quicker Tr
THE QUESTION(S) 1) Am I in error ?
2) Should I be using a compensation factor ?
3) Do I have incorrect data on the 370 material ?
4) Have the laws of physics forsaken me for some sin against the stray molecular particle ?
Any help would be greatly appreciated, especially on questions 1,2 & 3.
JOE SENDZ....
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