Ioan,
If the product is new, or repetitive order but still imature, then you may look ALSO at design problem. But, if this is a repetitive production of a mature product and the problem was not detected then I agree with Werner, but add to it the possibility of SJ problems between the balls and the component's substrate. I suggest to identify a problematic ball, then cross-section a failed board, and look at both sides using high magnification and even SEM.
Ofer Cohen
Seabridge - a Siemens company
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
> Sent: Friday, September 23, 2005 21:53
> To: [log in to unmask]
> Subject: Re: [TN] Soldering or design problem?
>
> Hi Ioan,
> Your heat/freeze=it works, ambient temperature=fail points to
> some intermittent opens
> 2 possibilities: (1) fractures SJs, (2) fractures PTV barrels.
> (2) is less likely, because it typically results in freeze=it
> works, heat/ambient temperature=fail;
> (1) is most likely given your descriptions. Have you tried
> press-down on BGA=it works? Your heat/freeze=it works is
> indicative of some BGA/PCB warpage.
> Possible causes: excessive BGA warpage due to thermlly
> unsymmetric design; thermal shock cracking due to rapid
> cooling after reflow.
> But, until you know what the problem is--let alone what the
> root cause(s) is(are), you cannot even think of a fix.
>
>
>
> Regards,
> Werner Engelmaier
> Engelmaier Associates, L.C.
> Electronic Packaging, Interconnection and Reliability Consulting
> 7 Jasmine Run
> Ormond Beach, FL 32174 USA
> Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
> E-mail: [log in to unmask], Website: www.engelmaier.com
>
>
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