Hi Carson,
I'd like to come back to your initial question.
HDI doesn't require special Prepreg Thickness, thus you can plan your Signal
related stack-up simply based on impedance requirements. For 99% of the High
speed part of the Designs, there is no benefit in using HDI. The major Benefit
is that it saves some Layers on dense electronic Boards and that can save
money, or leave more room in the Stack up for signal Layers with impedance
control.
As a example, a regular board with 20 Layer can have 4 impedance controlled
layer 2 Power Layer and 8 general Purpose Layer all on 2mm PCB Thickness.
Using HDI might reduce the general Purpose Layers to 4, giving you two extra
impedance Controlled Layer without changing the PCB Thickness at all.
BR
Gert
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Carson Au
Sent: Thursday, November 03, 2016 1:07 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] HDI and SERDES Channels
Hi Experts,
From my understanding, HDI build-up layers require thin prepreg layers, leading
to very thin trace widths for 100ohm differential impedance control
- and your high speed serial links would suffer great conductor loss.
How do you mitigate against this?
If your design has many build-up layers with thin build-up layers on either
side of your stripline, then it is impossible to even get something like 100um
(4mil) trace widths for your 100 ohm differential pairs!!
Regards,
Carson
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