[SI-LIST] Re: AW: FR4 Permittivity
- From: "Bill Hargin \(In-Circuit Design\)" <b.hargin@xxxxxxxxxx>
- To: <Gert.Havermann@xxxxxxxxxxx>, <cyril.chastang@xxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 21 Feb 2013 12:13:37 -0800
Hi Cyril:
As you're suspecting, a Dk of 2.173 is simply beyond the reach of FR-4. The
lowest Dk I know of for 370HR is 3.63, and that would be with 71% resin for
2 mil thickness, 106 glass at 5-10GHz. I don't the discrepancy here has
anything to do with resin content, frequency, or temperature, however, as
even 100% resin wouldn't get you to that value at any temperature or
frequency. I see this kind of thing at least once a week, where a PCB
fabricator - who is serving a bunch of customers every month - fails or
forgets to edit a value (Dk, Zo, Zdiff, etc.) from a previous customer's
stackup spreadsheet (or PDF, by the time it gets to you). In fact, this is
my second one of these *today*. (The other one involved FR406.)
It's one of those caveat emptor situations ("let the buyer beware"). In my
opinion, engineers should be planning and validating stackups themselves to
make sure that this foundational component of SI, timing, crosstalk, and
EMC is dialed in properly. Trusting your company's 1000s of hours of design
work to someone who has probably never designed a PCB, is serving 50++
customers per month, and who understands fabrication processes, but not
electrical details of your design doesn't make sense to me.
Our dielectric library (available in our eval) has the Dk numbers you're
looking for. (www.icd.com.au > Stackup Planner > Evaluation.)
Bill Hargin
In-Circuit Design, USA
Software & SI Simulation for High-Speed PCB Design
(425) 301-4425 b.hargin@xxxxxxxxxx Skype: bill.hargin
Online: www.icd.com.au
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Havermann, Gert
Sent: Thursday, February 21, 2013 5:16 AM
To: cyril.chastang@xxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AW: FR4 Permittivity
This isn't good data.
First of all, they only tested only once (you can tell that there is no
variation in their Test results).
Second, they don't specify the test Method they used, and there are official
test methods giving totally wrong results (the old 1MHz plate capacitor
method @ 1MHz used to be quite inaccurate).
Third, the Data is measured at 1MHz, thus these values are useless for
speeds exceeding 100MHz
I recommend to go by the Datasheet (Isola is usually very good at dk/df
testing), or test it on your own, but 2.173 is physically impossible for
glass reinforced resin as the glass altready has a much higher dk.
BR
Gert
----------------------------------------
Absender ist HARTING Electronics GmbH, Marienwerderstraße 3, D-32339
Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.: HRB
8808; Vertretungsberechtige Geschäftsführer: Dipl.-Kfm. Edgar-Peter Düning,
Dipl.-Ing. Torsten Ratzmann
-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von CHASTANG Cyril
Gesendet: Donnerstag, 21. Februar 2013 13:49
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] FR4 Permittivity
Apparently, the screenshot is invisible in my previous email. I have the
following data:
Grade: PLC-FR-370HR H/H(RTF)
Thickness: 0.004 in
Customer: SanminaSIN
Test Property | Unit | Condition
| Sampling | Test Results | Specs
Dissipation factor | - | IPC-4101*A C-40/23/50
@1MHz | 1/month | Ave: 0.007 [0.007 - 0.007] | 0.035
Diectric constant | - | IPC-4101*A C-40/23/50
@1MHz | 1/month | Ave: 2.173 [2.173 - 2.173] | 0-5.4
Thank you.
Best regards,
Cyril
________________________________________________________
Hi,
I have recently received a PCB (dielectric= Isola PLC-FR-370HR) and its
certificate of compliance (extract below). The value of the material
permittivity given below is quite surprising (2.173) to be FR4. Is it the
effective permittivity for a microstrip? Is there a mistake in the
certificate?
Have you ever seen a FR4 permittivity like that ?
Thank you for your help.
Cyril
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