Naresh,
Here is more on the flex PCB analysis
https://lnkd.in/gA6zbie8 ;
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
www.simberian.com
Simbeor - Be The SI Expert!T
Simbeor THz - Accurate, Productive and Cost-Effective Electromagnetic Signal
Integrity Software to Design Predictable Interconnects!
Simbeor SDK - The Industry-First Signal Integrity Analysis Automation Kit!
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Naresh Varikuntla
Sent: Wednesday, June 7, 2023 9:45 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Flex PCB for PCIe
Thank you Bill Hargin,Yuriy Shlepnev, Stephen Btotman,Havermann Gert,
Elliott Martison.
Thank you very much for sharing the information . I need some time to
understand the information that you have shared.
On Tue, Jun 6, 2023 at 1:01Б-│AM Bill Hargin <billh@xxxxxxxxxx> wrote:
Hi Naresh:reference
Looks like you're getting some good feedback here. I think you would
benefit from reading chapter 7 in a stackup design ebook that I wrote last
year. You can download it for free from https://i007ebooks.com/su ;.
The end of that particular chapter goes into some of the issues Stephen
Raised below. One trick that a lot of people aren't aware of is to align
your Differential Pitch with the Diagonal Pitch of the associated
layer, which is probably advisable at PCIe speeds.itself,
If you want to check out a tool that will help you do this, including
dialing in differential impedance and calculating the insertion loss, let
me know and I can set you up with an evaluation of our Z-planner stackup
tool. (Also, chapter 3 in the ebook noted above covers loss with a PCIe
example.)
Bill Hargin
Z-zero БvL Innovative PCB Stackup Design БvL www.z-zero.com
billh@xxxxxxxxxx БvL 425-301-4425
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On
Behalf Of Stephen Brotman
Sent: Monday, June 5, 2023 7:30 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Flex PCB for PCIe
From what I understand with flexible PCBs, enhancing reliability can
involve minimizing the use of adhesives, which translates to using an
adhesiveless copper laminate (I've used DuPont Pyralux AP and Panasonic
R-F775 in the past) and sticking with a single-layer or adhesiveless
two-layer stack-up to eliminate the need for bond-ply. For the bend
the closer your traces are to the neutral bend axis, the less likely theypairs
will experience fracturing. Away from this axis, I've read that small
traces do better towards the inner bend experiencing compression (as
opposed to the outer bend experiencing tension). Above all, always stay
within minimum bend radius limits.
With flexible PCBs the reference plane is often cross-hatched to maintain
flexibility, and your signal would be routed over periodic gaps in the
reference plane. This will lead to increased radiation, although I haven't
seen this cause EMI issues with differential pairs. With differential
you'd want to ensure they are routed symmetrically above thiscross-hatched
reference plane to minimize skew. Polar Instruments application note AP534trace
talks generally about hatched ground planes, and this symmetry I mentioned
is illustrated there.
If you use stiffener material on the same side as external controlled
impedance traces, the impedance will increase when your traces transition
into those regions. To minimize reflection, you'd want to adjust your
width in those regions with stiffener.
Best,
Stephen
On Mon, Jun 5, 2023 at 9:49ц-Б--б│AM Elliott Martinson <
emartinson@xxxxxxxxxxxxx>
wrote:
From some quick research, the dielectric constant is lower (3.2-3.4 vs.
4-4.4), so for controlled impedance circuits, thinner board + thinner
line widths and spacings ц©ighter minimum bend radius.
The material is uniform and so the "glass weave" effect in FR4 is
eliminated The copper is rolled annealed with a horizontal and
elongated copper grain structure vs. FR4, which is electrodeposited
with a vertical grain structure. The effect is mechanical, where
copper on the flex is more reliably bent. But there is a reliability
concern where moisture absorbed by the polyimide can--when heated
(such as in assembly)--turn to steam and cause damage, which is why it
is typically baked in an oven before assembly
FR4 has a max operating temperature of 150ц-б│C vs. flex цЁ00ц-б│C Loss
tangent is lower for the flex. Polyimide's ц©003-0.01 while FR4 is
0.02 to 0.03
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On
Behalf Of Naresh Varikuntla
Sent: Sunday, June 4, 2023 6:41 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Flex PCB for PCIe
Hello SI Community,
I am looking at flex PCB for routing PCIE gen3 and PCIe Gen 4 due to
space restrictions. Flex PCB route length could be around 4 Inch.
I do not have prior working experience on flex PCB. I need your help.
1)Could you please help me to understand the likely problem with flex
PCB considering signal integrity and EMC?
2)How to estimate the loss of flex PCB?
3)How to improve Reliability flex PCB in a harsh environment?
Also kindly share your experience with Flex PCB for high speed signal
routing.
Thank you in advance,
Naresh V.
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