[SI-LIST] Re: Loss Tangent of Solder Mask
- From: "Eric Sweetman" <eric@xxxxxxxxxxxxxx>
- To: <scott@xxxxxxxxxxxxx>, <ray_waugh@xxxxxxxxxxx>
- Date: Fri, 7 Mar 2003 08:30:01 -0800
Scott,
Did you also measure microstrip losses without soldermask? Also, what =
was the surface treatment of the microstrip metal? At Lucent, we found =
that microstrip losses without soldermask were varied considerably =
between unplated Cu, solder-plated CU, HASL Cu, and a couple of =
different Ni plating processes. Unfortunately, I don't have the =
information in my possession anymore.
Eric Sweetman
-----Original Message-----
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Thursday, March 06, 2003 8:49 PM
To: ray_waugh@xxxxxxxxxxx
Cc: cnepsc@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Loss Tangent of Solder Mask
Ray,
Actually with coplanar waveguide over ground the loss effect of=20
soldermask should be higher than even microstrip, due to the field=20
intensity within the gap. I suspect that you see little difference due=20
to your relatively short length.
When I was with another company, we made some measurements of microstrip =
and stripline traces on a very long test backplane structure (>20").=20
The microstrip traces were wider than the stripline traces and our=20
field solver predictions with Ansoft 2D showed that we would have=20
marginally lower loss with our microstrip traces embedded in soldermask. =
In this case we assumed that the loss tangent was about the same as the =
FR406 we were using, about 0.02 in the 1 to 20 GHz range, or so. In=20
fact, when we performed side by side comparisons, we found that the=20
microstrip conductors had significantly higher loss by about 50%,=20
consistent with a higher loss tangent for the soldermask. At this point =
we discontinued our investigation and decided that for long traces it=20
would not be a good idea to use microstrip routing.
Some day I always thought it would be a interesting idea to investigate=20
the loss properties of different soldermask materials on a series of=20
test boards with a substrate material that has well controlled=20
properties, like the Rogers 4000 series.
best regards,
scott
--=20
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
ray_waugh@xxxxxxxxxxx wrote:
>Neeraj...
>
>What we use is coplanar waveguide over a groundplane, on the top of a =
single-layer board 0.032 inch thick (ground plane on the bottom). This =
makes for nice, easy-to-etch dimensions for line and gap. We put the =
solder mask on the top, and it goes into the gap. However, I must admit =
that our boards are short, with lines that are generally two inches or =
less in length.
>
>Ray
>
>Raymond W. Waugh
>Agilent Technologies
>
>-----Original Message-----
>From: Neeraj Pendse [mailto:cnepsc@xxxxxxxxxxx]
>Sent: Thursday, March 06, 2003 4:12 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Loss Tangent of Solder Mask
>
>
>
>Ray,
>
>Regarding coplanar wavegiudes, I have a question: are these buried or =
on
>the top layer of the PCB? If they are on the top layer, then wouldn't
>the deposition of the solder mask affect the area between the traces?
>
>- Neeraj
>National Semiconductor Corporation
>
> =20
>
>>ray_waugh@xxxxxxxxxxx wrote:
>>
>>Michael...
>>
>>Unless you are forming a transmission line using a conductor over a =
ground plane with solder mask as the dielectric, it does not much =
matter. If you are concerned about solder mask over the top of a =
microstrip line (for example), the e-fields above the line is so weak =
that you'll never be able to tell (by measurement) if there is solder =
mask there or not. We commonly use solder mask on our 2 GHz CDMA test =
boards (on top of microstrip or coplanar waveguide lines) and it has no =
effect whatsoever.
>>
>>Ray
>>
>>Raymond W. Waugh
>>Agilent Technologies
>>
>> =20
>>
>
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