PAD size for Edge Mount SMA Connector - RF Cafe Forums
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Post subject: PAD size for Edge Mount SMA Connector
Posted: Mon Dec 29, 2008 7:44 am
Wed Aug 16, 2006 8:20 am
I am using
an Edge mount SMA connector to feed CPWG lines on my PCB. The Application
notes form The SMA manufacturer recommends 70 Mils wide pad for the
central conductor pin which is 50 mil diameter and 150 mil long.
While making the footprint I used the same dimensions mentioned by the
On simulating the PCB uisng a 2D solver, I found that
the return loss was very poor. My GND plane was 20 Mils below the Signal
trace. Since I am using a multilayer PCB the stackup gave a total thickness
of 64 mils as required to fit in the SMA connector.
I cleared the
GND on all layers below the SMA signal PAD and used the lowest layer
(at 64 mils form the signal layer) as the GND layer, in order to reduce
the parasitic capacitance. the performance did not improve much.
Please share your comments and suggestions to improve the return loss
Design Engineer- RF
Post subject: Posted: Sat Jan 10, 2009 12:42
Joined: Mon Jun 27, 2005 2:02 pm
First of all
your CPWG thickness should create 50-ohm impedance and should be calculated
accordingly. There are different types of SMA connectos, some have 2
GND pins aligned with the central conductor and some have 4 GND pins.
From your description I assume you use the 4 pins type.
try to see if there are also connectors with different width of the
As for the GND conection - you should connect
the GND on the top with vial holes to the other layers for formation
of a continuous GND plane.
subject: Posted: Tue Jan 13, 2009 2:37 am
Joined: Wed Aug 16, 2006 8:20 am
I am using the 4 GND pin SMA connector. I cannot
change to a different width SMA connector now as the part has been already
ordered. The 70 Mil wide pad suggested by the vendor for SMA center
pin gives an impedance as high as 75 Ohms (VSWR of 1.5) at 7 GHz. I
tried to reduce the pad width to 50 ohm (exactly the same as the center
conductor diameter), and got a VSWR of less than 1.2
I am afraid
that reducing the PAD to 50 mil width would create some problem during
Post subject: Posted: Tue Jan 13, 2009
Joined: Mon Jun 27, 2005 2:02
From my experience, I do not
expect any problems with the soldering of the SMA connector. ..