Bill,
From what I know from previous attempts... Since most materials don't
adhere well to teflon, when making a mixed dielectric board, it is
important the have lots of copper on the telfon core. The board
manufacturer is relying on the FR4 prepreg to "stick" to the copper, and
not really the teflon.
As far as reducing RF losses, for the sake of argument the we will
assume it is a stripline environment, it is dependent on your return
paths. In this case if the teflon dielectric is greater than the FR4
dielectric, the majority of your electric fields will be in the
dielectric with the closer return path, in this case the FR4. This
would diminish the reason for using the teflon in the first place.
Accepting of the fact that this is a first order approximation of the
effect, only a good 2D field solver simulation of the cross-section and
loss would give you the correct answer.
My understanding is that assembling a board with mixed dielectrics is
possible, but your SI has to be sound. Otherwise it is all for nothing,
sort of. There may be some benefit, but it may not offset the cost of
such a material.
Contact me offline, if you would like to know more.
Devon
========================================================================
Devon J. Post - C.I.D. Mayo Foundation
<mailto:[log in to unmask]> 200 First Street SW
Voice: (507) 538-5479 Sn 2-134C
Fax: (507) 284-9171 Rochester, MN 55905
Internet: http://www.mayo.edu/sppdg/sppdg_home_page.html
========================================================================
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Brooks,Bill
Sent: 27 February, 2007 10:58 AM
To: [log in to unmask]
Subject: [DC] PTFE 'Teflon' combined FR4 boards...
Hello Designers council... :) Good morning!
It is raining here in San Diego today... (Contrary to popular belief, it
does rain in California... :))
New subject... Does anyone have any data they can share on Teflon/Fr4
bonding of mixed board materials and a guide to the use of them? I have
some
interest in the subject and would like to get more educated...
I hear claims that this is being done a lot and would like to see some
examples and read about the reliability and manufacturability of the
mixed
materials and what are the benefits and pitfalls of choosing this
combination as a solution to reducing the RF loss in a board due to the
dielectric properties?
Best regards,
Bill Brooks
PCB Design Engineer, C.I.D.+
Tel: (760)597-1500 Fax: (760)597-1510
Datron World Communications, Inc.
Vista, California
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