Motorola has published papers on the effect of soldermask versus non soldermask defined pads on BGA reliability (Motorola Customer Applications Support and Reliability Test Center- try Digital DNA from Motorola web search . I would guess that these diamond pads would function the same as Solder Mask Define Pads in that it would effect the bonding area on the PCB pad and change the strain distribution within the joint. 

Tom Gervascio
Senior Process Engineer
Sparton Electronics
(352) 540-4040

>>> [log in to unmask] 07/23/04 10:16AM >>>
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

--
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560

Direct: (919)653-4249
Main: (919)653-4180
Fax: (919)653-4297

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