Bill, I might broadly suggest some kind of contrast approach.  Take a 
good board, make a suitable image of it, then take the bad one, image it 
and compare images.  I believe IC makers use voltage contrast with 
electron microscopes to look for inactive regions.  that would be 
expensive, presumably.  Other things, like thermal contrast or 
holographic image would likewise not be cheap, I suspect.   Lou Hart


.

On Tue, 13 Aug 1996, bill birch wrote:

> We are looking to support our colleagues at various PWB testing 
> facilities, who are looking for an effective methodology for identifying 
> the locations of failure sites following accelerated stress testing.  Our 
> present method utilizes an infra red thermal imaging system, 
> inconjunction with a low level (milliamps) DC current supply that creates 
> the necessary temperature differences to uncover the exact position of 
> one or multiple defect sites.
> 
> 	The cost of thermal imaging equipment is prohibitive for most 
> companies, we are looking for a lower cost alternative that has the 
> following capabilities:
> 
> 	Ability to uncover partial failures, defects that have not fully 
> propagated to an open state (opens are easily found with conventional 
> multimeters).
> 
> 	Ability to identify intermittent defects that are not detectable 
> unless the test vehicle is elevated to a temperature close to the 
> laminate Tg.
> 
> 	Ability to isolate (identify) defect location.
> 
> 	We are open to any suggestions/recommendations.  We are 
> interested in any additional information regarding "thermal tapes/inks" 
> that can be applied to the surface of the test vehicle, to identify 
> localized temperature differentials.  Electrical testing fixtures that 
> could accommodate the passing of DC current through the test vehicle 
> during the fault finding. 
> 
> Respectfully,
> 
> Bill Birch
> PWB Interconnect Solutions Inc.
> 
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