Post subject: Solder Mask on RF PCB Posted: Fri
Jan 23, 2009 10:55 am
Joined: Wed Aug
16, 2006 8:20 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
Has anyone faced a similar problem or has any
Post subject: Posted:
Fri Jan 23, 2009 5:36 pm
Jun 27, 2005 2:02 pm
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...
Post subject: Posted: Sat Jan 24, 2009
Joined: Wed Aug 16, 2006 8:20
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.
Design Engineer- RF