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>Reply-To: "TechNet E-Mail Forum." <[log in to unmask]>,
>        Yvon Hache <[log in to unmask]>
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>From: Yvon Hache <[log in to unmask]>
>Subject: [TN] FR4 dielectric constant
>To: [log in to unmask]
>
>Hello out there,
>
>My weekend seems longer now that we have designated "Steve's day" on Friday.
>
>I am a design engineer and started working with RF stuff on this last
>design.  I am doing the calculation for a microstrip width for a FR4 PCB,
>0.062" thick.  What would be the dielectric constant of this material?
>
>Yvon Hache
>Design Engineer
>Concept + Inc.
>
>T: 506-863-2467
>F: 506-858-4075
>[log in to unmask]
>www.concept-plus.com
>
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Dear Yvon,

Most laminate suppliers give Er for FR-4 @ 1 MHz in the range of 4.5 to 4.7
depending on core type and pre-preg finished glass/resin ratio.

For controlled impedance designs you need a figure for typical Er at a much
higher frequency, say 1 GHz.  Er for FR-4 @ 1 GHz is typically in the range
of 4.0 to 4.3 for these types of material.

Watch out for the allowance of the air dielectric around the trace in surface
microstrip designs and also for soldermask effect (SM reduces impedance
of surface microstrip traces).

Hope this helps.


Best regards

Andy Burkhardt
Product Manager
Email: [log in to unmask]
Tel: + 44 1481 253081
Fax: + 44 1481 252476
http://www.polar.co.uk
=====================================================
World leaders in PCB faultfinding and controlled impedance measurement
=====================================================

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