FEDEVEL
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michaelchang , 11-07-2017, 04:07 PM

Hello,

According to our PCB manufacturer's calculation, the trace width will be above 0.2 mm in order to keep 40 Ohm single ended impedance.

I found that it was impossible to fan out this trace from BGA (0.8mm pitch). I have to make it thinner, thus I can't keep required impedance under BGA. I did some research online, someone said it shouldn't be an issue with such a short distance of trace without impedance control. I am not sure if this kind of impedance mis-matching will cause any reflection big enough to affect signal quality.

I am wondering how you guys deal with this kind of situation in your design?

Thank you!

robertferanec , 11-07-2017, 07:43 PM

I have seen many designs with tracks thinner under BGA.

PS: However, I have never really needed this, so I can not say from my own practical experience.

michaelchang , 11-08-2017, 04:29 PM

Thanks, Robert.
I think maybe this is the only option for me to fan out the tracks.