Yes, I have heard of this, but with respect to x-ray inspection, not optical. On the x-ray its easy to see if the extension of the pad has been wetted by the ball. Its not as easy to see if a ball/pad has flowed if the ball is completely in line with the pad. The 'extension' whether it be a teardrop, or just a trace stub, needs to be unmasked. I suspect that optical and x-ray inspection has improved to the extent that this technique probably isn't as useful as it once may have been.
Gary Crowell
Micron Technology
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Seymour
> Sent: Friday, July 23, 2004 2:55 PM
> To: [log in to unmask]
> Subject: Re: [TN] BGA Land Patterns
>
>
> This request is not for Soldermask defined pads.
>
> The Request is for diamond or a tear drop shaped
> copper land patterns for the BGA pins. Just curious if
> anyone out there had seen this.
>
> Thanks,
> dave
>
>
> Werner Engelmaier wrote:
>
> >Hi Tom,
> >The problem with SMD-SJs [solder-mask-defined] is that the
> SJ geometry
> >results in a stress concentration where it is shaped by the
> solder mask--it has
> >nothing to do with bonding area or overall strain distribution.
> >
> >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
> >
> >
> >
>
> David Seymour wrote:
>
> >To All,
> >
> >
> >
> >I just had an assy house recommend a diamond shape
> >
> >or tear drop shape for a BGA land pattern to allow for better
> >
> >optical inspection related to reflow and solder opens detection.
> >
> >
> >
> >Has anyone come across a white paper or reliability study
> >
> >for or against alternative pad shapes for BGAs?
> >
> >
> >
> >dave
> >
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>
> --
> Dave Seymour, CID+
> Catapult Communications Inc.
> 800 Perimeter Park Dr, Suite A
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>
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> [log in to unmask]
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