[SI-LIST] Impedance Mismatch due to neck down

Hi Experts,
The board that I am using is of a stripline setup with 8mil traces (1 oz
Cu), FR-4 (4.0) and 10 mil dielectric thickness which gives 50ohm
(relatively low speed). The BGA is tightly pitched and I have to neckdown
traces around 4-5 mils which gives impedance mismatch (65.4 ohm). Neckdown
is a must but I also want to avoid impedance mismatch, is there any way of
doing it? Does doubling help? (looks like this would give a parallel of 2
65.4ohms = 32.7, worse than what I have).

Thanks in advance,
Qazi






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