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Solder Mask on RF PCB - RF Cafe Forums
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ashishbondia
Post subject: Solder Mask on RF PCB Posted: Fri Jan
23, 2009 10:55 am
Captain
Joined: Wed Aug 16, 2006
8:20 am
Posts: 23
Location: India
Hi!
I am designing a
PCB to work from 100KHz to 7 GHz. I was almost done with my Layout and
the gerber was ready for fabrication when someone mentioned to me that
I should consider the effect of Solder mask.
He suggested that the
Grounded CPW trace width and separation I used were valid only when
I had air as the dielectric over my traces. Using a Solder mask would
alter the impedance as it has a dielectric greater than air.
I quickly
added a layer of Solder mask in my simulation (using Er for Solder Mask
as 3.3 and loss tangent as 0.04
I found that The VSWR of my trace
improved, however the trace was now more lossy.
I don't want
to get rid of the solder mask as the Coplanar GND plane is just 20 mil
away from the RF trace and many (0402) size components need to be soldered
on them. Since I am not very good at soldering I am afraid that I would
short the traces. My board is fairly large (10 inches by 7 inches) and
has more than 500 components. Few traces are 1 inches long.
Has anyone faced a similar problem or has any suggestions...
_________________
Ashish Bondia,
Design Engineer- RF
Top
IR
Post subject: Posted: Fri Jan 23, 2009 5:36 pm
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts:
373
Location: Germany
Solder mask at frequencies higher than
4GHz is not recommended because it adds insertion loss. Do not worry
about soldering, once you start you will improve with time. But if you
will miss 1-2dB gain in your Tx chain it will be much harder to compensate...
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ashishbondia
Post subject: Posted: Sat Jan 24,
2009 4:44 am
Captain
Joined: Wed Aug 16, 2006 8:20
am
Posts: 23
Location: India
Thanks IR
I am exploring
the possibility of using Solder Dams to restrict the flow of solder
on the bare traces.
However for a board having more than 500 component,
the time required to create Solder dams along each pad would be large.
Along with the Solder mask another issue that is driving me
crazy is that of Board Surface finish. I have a choice of HASL and ENIG
finish. I have learnt that ENIG causes higher insertion loss and also
degrades IMD performance.
_________________
Ashish Bondia,
Design Engineer- RF
Posted 11/12/2012
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