FreeLists / si-list / [SI-LIST] Re: Loss Tangent of Solder Mask

["Scott McMorrow" <scott@xxxxxxxxxxxxx>]

Michael,

Dispersion is certainly a possibility, although it is generally 
minimized with differential transmission, since the above FR4 fields 
tend to want to concentrate between the traces and the soldermask has a 
dielectric constant that is close to that of FR4.

I always wanted to run a controlled experiment that would measure all 
the possibilities of loss with and without soldermask,along with the 
losses of different soldermask materials. Just never had the time.

scott


Michael Khusid wrote:

>Scott, Gustavo,
>
>Based on the description of the experiment, I thought that dispersion
>may something to do with the perceived loss of signal magnitude in the
>microstrip structure. In brief, the dispersion is caused by the
>difference of dielectric constants, and thus, different propagation
>speeds of the high frequency signal content in different layers. The
>difference of propagation speeds causes deformation of the edge as
>measured in time domain.
>
>While stripline dielectric layers make relatively homogeneous structure,
>microstrip is surrounded by at least three very different dielectric
>layers - FR4 on the bottom, aforementioned soldermask, and air above
>that.
>
>Mike
>
>-----------------------------------------------------------------
>Michael Khusid
>Ansoft Corporation
>SI/HF Application Engineer
> 
>25 Burlington Mall Road, 6th floor
>Burlington, MA 01803-4100
> 
>Tel 781-229-8900 Ext. 34
>Fax 781-229-8624
>--------------------- http://www.ansoft.com ---------------------
> 
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of gustavo.duenas@xxxxxxxxxxx
>Sent: Friday, March 07, 2003 1:02 PM
>To: scott@xxxxxxxxxxxxx
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Loss Tangent of Solder Mask
>
>
>
>Scott,
>
>I saw an app note from Accelerant Networks (16_0008_A.pdf) that states
>the
>loss tangent of solder mask is rather lower than fr4 (0.001), yet you
>said
>you determined it must be higher than 0.02? Are there different types of
>maks? Anybody would like to clarify? I'd appreciate it.
>
>Thanks,
>
>Gus
>
>*******************************************************************
>Michael,
>
>At the time we believed that the loss tangent of soldermask was about
>0.02.  Based upon high frequency eye losses that we were seeing, we
>determined that the loss tangent must be higher.  We didn't make any
>additional measurements to determine the loss tangent precisely, nor did
>we go back and make corrections to our model and resolve for the higher
>loss tangent.
>
>scott
>
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-- 
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com




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