Hi Kevin - We have done some trial work of attempting to apply ultrasonic
technology as a method of crack detection in BGA solder joints without
success. The major problem was there are two many " reflection interfaces"
which compete with the goal of looking at the potential crack interface of
the BGA joint on a printed wiring assembly. The potential for ultrasonics
to be helpful was not ruled out but more work was needed in basic
ultrasonic signal detection/manipulation. We have also done some work with
Xray technology but as Werner and others have pointed out there was more
relevant data obtained with electrical test methodology (i.e. boundary
scan). The major problem with xray techniques was lack of resolution needed
in relation to the crack geometries encountered within a single material of
high density (i.e. lead). The crack sizes are in the noise limits of the
xray resolution measurements.  Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




[log in to unmask] on 01/01/98 09:18:05 PM

Please respond to [log in to unmask]; Please respond to [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: David D Hillman/CedarRapids/Collins/Rockwell)
Subject:  Re: [TN] Crack detection under BGA?




I doubt ultrasonics would help you.  Accelerate the cracks to failure.  The
quickest/least expensive way I know of accelerating cracking is thermal
cycling/thermal shock.  Best way to detect opens is to do an electrical
test.  Checking many 100s of interconnects for (dis)continuity during
vibration can be tricky (unless we're just talking about test BGAs and test
boards rather than actual assemblies).  Take a decent sample of parts, test
for continuity, temp cycle them and then re-test.  If you have any
failures, repeat the temp cycling on the units which passed and re-test
again.  This will give you some confidence that you're screening out
something.  Analyze the failures to determine the root cause of failure.
At 11:24 PM 12/31/97 -0500, Bev Christian wrote:
>Werner and all,
>Does anyone know if the ultrasonic methods for delamination detection in
>components are powerful/sensitive enough to look through BGAs to find
>either gross opens and/or hairline cracks in the BGA solder joints ?
>
>Bev Christian
>Nortel
>
>>----------
>>From:  Engelmaier[SMTP:[log in to unmask]]
>>Sent:  Wednesday, December 31, 1997 5:39 PM
>>To:    [log in to unmask]
>>Subject:       Re: [TN] Crack detection under BGA?
>>
>>Hi Kevin,
>>The only way you have a chance of finding cracked solder joints in
product
>>with BGAs is to functionally test while subjecting your assemblies to
>>vibration. This gives you a chance of finding fully fractured solder
joints,
>>as well as use the vibration as a screening test for latent defects.
However,
>>with BGAs, I am not certain that even this method is 100% effective.
>>
>>Werner Engelmaier
>>Engelmaier Associates, L.C.
>>Electronic Packaging, Interconnection and Reliability Consulting
>>7 Jasmine Run
>>Ormond Beach, FL  32174  USA
>>Phone: 904-437-8747, Fax: 904-437-8737
>>E-mail: [log in to unmask]
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