Posted by yy_sia: Wed May 21, 2008 4:52 pm    Post subject: Detection of sagging wire thru electrical test

Hi all,

Is there any way that sagging wire can be detected thru electrical test? As far as I know, leakage test is one of the main test parameter which can be use to detect this failure. But, how good is the sensitivity? Any other test to confirm a better reliability?

Thanks,
YY

Posted by Sebastian: Wed May 28, 2008 4:10 pm    Post subject: Re: Detection of sagging wire thru electrical test

YY,

I think you are right by saying that leakage test response can be used to detect sagged wires. However, there may be other defects whose electrical test response is leakage (like two or more wires very close to each other) so this is not reliable. X-ray would most likely confirm it.

Also, you may want to explain why you wanted to trap this sag wire problem at Test. Why not address it at assy, particularly within the WB-Mold areas? It's kinda late correcting this problem at Test.

regards...

Posted by FARel Engr: Tue Jun 03, 2008 11:22 am    Post subject:

Hi YY,

Sagging wires per se can not be detected by electrical testing.  Exception is if they are gross enough to create electrical paths that divert the natural flow of current in the circuit, such as a wire touching another wire or a wire touching an unpassivated edge of the die. Another scenario is when testing a high-speed device under high-frequency operation, in which case the higher inductance caused by the sagging wires can affect device performance even if the wires do not contact other live parts of the circuit.

The failure modes that can result when sagging wires touch greatly varies – from just a marginal leakage to a dead short to ground that can cause EOS, depending on which parts of the circuit are bridged by the sagging wire. 

Thus, to answer your question, electrical testing is not a good way to detect wire sagging because: 1) wire sagging does not always cause electrical failures and 2) if they cause electrical failures, the failure mode is unpredictable. I therefore agree with Sebastian that x-ray inspection is more effective in detecting wire sagging issues.

Good luck!