[SI-LIST] Re: SI Testing of connector without a fixture
- From: "Jim Nadolny" <heavyside@xxxxxxxxxx>
- To: "padma gundala" <pgundala2001@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Sun, 31 May 2009 08:06:18 -0400
Greetings Padma -
I think you will get an idea of any gross insertion loss problems with this
method.
My guess is that most companies in the connector industy have used this
technique at one time or another with mixed results. On the plus side - it
is quick. On the down side - your results will likely be dominated by your
soldering/fixturing skill level. What I have done with OK results is to use
0.062" thick copper clad PCB material for my ground plane. The thin foil is
not to difficult to solder to and the glass epoxy substrate is easy to
drill. Make sure your semi-rigid probes are phase matched, particulalarly
if you are trying to get a differential crosstalk value.
The probe to connector interface is almost always inductive with this
technique and that is a measurment artifact. When the connector is mounted
on a real world PCB - the connnector to board interface will likely be
capacitive...so that is one problem. Bottom line here is that you can't
really believe the impedance profile/return loss measurement that you get.
You are on the right track with having all the return paths connected to a
common ground plane. If you were trying to measure NEXT/FEXT, that would be
very critical.
Also the connector performance comes into play. If you have an "old school"
2 mm HM backplane connector that has a pretty long signal path, this
technique will give you an idea of what's going on. If you are trying to
measure a 5 mm tall board to board connector, well they woud be about
invisible with this technique as they are so short.
If this is a modern connector (developed in the past 5 years) and it is
supplied by a major manufacturer you ought to be able to request a
performance report. I'll caution you that you need to pay attention to how
the data was obtained to understand what was tested (connector, connector +
footprint, connector + test board, etc.)
Hope this helps....
Jim Nadolny
----- Original Message -----
From: "padma gundala" <pgundala2001@xxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Saturday, May 30, 2009 4:03 PM
Subject: [SI-LIST] SI Testing of connector without a fixture
> Hi,
> I am planning to test a connector without a test fixture. (The connector
> is designed to be suitable for SMT soldering to PCB/BGA Packages)
> I was thinking of a quick low cost method.
> Solder a thin flexible co-axial cable with an SMT connector at one end to
> connect to TDR/VNA.
> I plan on testing a differential pair. All the surrounding mated
> pin/sockets  to be soldered to a copper plate with a cutout at the signal
> pair .
> My question is how thick should the copper plate be. Â Also has anyone
> tried this method. Â Were the results accurate enough.
> If it works well for TDR, I was thinking of testing S Parameters on the
> VNA. I accept that there will be losses embedded from the short (2â??)
> co-axial cables/SMT for the VNA measurements.
> At least I will get an idea about the connector performance.
> Any thoughts/ feedback or better ideas will be appreciated.
> Thanks,
> Padma
>
>
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