[SI-LIST] Re: need help with micro probes

  • From: Gustavo Blando <Gustavo.Blando@xxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Wed, 15 Aug 2007 21:00:43 -0400

Please read bellow after GUS:

Hi Experts,
I am just starting / trying to do high speed measurements with pico probes
and would like to get some feedback how to do it right.

I have GGB model 40A pico probes, a GGB CS-11 calibration substrate and
Quater research XYZ500 micropositioners.

GUS: Not familiar with the XYZ500 positioners, have a different one, but
have used CS-11 and GGB 40A probes.


What's the recommended magnification for the microscope to place the probes?

GUS: Not entirely sure I understand your question, or maybe your setup, but
you just need to make sure you clearly see your landing. Most of the times
it's easier just looking on the u-scope directly, (not digitally on a
monitor) since there is a much better 3D feel and you'll be able to see
depth better.

How do I know, when the probe tip touches the calibration substrate or the
DUT

GUS: Some VNAs during calibration will forced you to a particular view, this
is my case when doing guided-cal, (magnitude only visible), If this is your
situation I would recommend land the probes first on the CS-11 50Ohms load,
then you'll clearly see when the probe is landed (you should see a low and
slowly increasing return loss). You can't see this, when looking at
magnitude on a short or open. 
After you set the angle position of your probe on the 50 Ohms you are much
more likely to get a good landing on the short and open using the same probe
angle.

If your VNA allows you to view two channels simultaneously when calibrating
in one of them, you can set the un-calibrated channel to view the phase.
With that, now you'll see the phase change by 180degrees on a short. 
On the open, you can put a pointer on the phase on the un-calibrated channel
and you'll see the angle change bit, not much, but at least is some
indication.

GUS: Summary.
     
If your VNA allow viewing only one channel during cal:
- Set the channel to magnitude
- Land first on the 50Ohms and make sure the contact is good with not to
much pressure
- Then proceed with the cal.

If your VNA allows to view two channels simultaneously:
- Follow the above list +
- Set the additional channel to view phase. 

How far do I overdrive to get good contact of teh probe to the calibration
substrate or DUT

GUS: Here, you'll need some practice. If you are using the probes that are
pretty long, (S like) then probably you can start by doing this:
-Land the probes on the white ceramic area just passing the 50Ohms(for
example)
- When you see the probes touching the white ceramic piece, push a bit more
such the probe slides just a bit on the white part
- Bring the probes back towards the 50Ohms cal, you should see a bit of an
scratch both on the tip and ground when moving through the gold part. (It's
important you bring your probes back to the substrate and never push,
because if you do, the probe will jump an the GND blade will start to weaken
and deform)
- Look at the screen and see if you got a good landing.
- If you did, on that position, lift the probe and put it down again, with
no much pressure you should have a good landing.
- If you did not make good contact, adjust a bit the angle and repeat the
procedure from the beginning.

For the through on the calibration substrate, how do I control how far I
need to go from the edge to the inside, so that I probe the right lenght of
the through.

GUS: Please review the CS-11 manual, in there they show you a nice picture
for the proper through positioning with respect to the edge.
GUS: Hope this helps.

Any help / feedback is greatly appreciated,
Axel

Regards
Gus

       
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