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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