Guenter,

For what it's worth, I basically agree with you.  I have a really good Sonix
ST1000 with a nice collection of transducers.

I have not been extremely successful in getting quality images of the inside
layers of PWBs.  As you indicated, the glass mat really messes up the image.

With the proper set-up, one can sometimes pick up gross mousebites, or gross
necking of conductors, but I will not be so bold as to claim the ability to
pick up "cracks" in internal conductors (the boards I've played with are
only 3-4 layers thick).

Suggest the interested parties send samples to Sonix and/or Sonoscan for
evaluation.  A contact at Sonix is <[log in to unmask]>

Steve Creswick
CTS RFIM








At 04:55 PM 2/21/01 +0100, you wrote:
>Susan, Hans
>
>If these people are actually talking about an acoustic microscope forget to
use it to find broken traces in a PCB.
>- Cracks in traces tend to be quite thin. The smaller the features you want
to see, the higher the frequencies are you have to use for US- inspection.
On the other hand, the higher the frequencies the smaller the penetration
depth of the ultrasonic waves. If you want a lateral resolution in the 100um
you inspection depth is some um.
>
>- Polymers damp the ultrasound too much. The signal is very weak.
>
>- PCB's are reinforced with glass fibres. Each fibre gives you a signal.
Sure, you can filter that out to a certain extend in the time of flight
graph. However, we tried that and the pictures where not satisfying at all.
It might work for traces right below the soldermask.
>
>
>Maybe one finds some nice pictures for a special case in a prospectus of a
acoustic-microscope vendor but I am not convinced yet that this technique is
applicable for PCB's
>
>Best regards
>
>Guenter
>
>Guenter Grossmann
>Swiss Federal Institute for Materials Testing and Research EMPA
>Centre for Reliability
>8600 Duebendorf
>Switzerland
>
>Phone: xx41 1 823 4279
>Fax :      xx41 1823 4054
>mail:     [log in to unmask]
>
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