Hi Glenn!

Don't have a real concrete answer for you, but as you probably already know,
everything I've read recommends NSMD pads over SMD pads. I found figures of
ball collapse that range from 20-25%, but those figures were all referencing
NSMD pads.

Sorry I couldn't be more help...

But during my search, I found this excellent *.PDF file regarding PBGA's,
covers just about everything...

http://e-www.motorola.com/brdata/PDFDB/docs/PBGAPRES.pdf

-Steve Gregory-


> Technetters,
>
>         There is a proposed design here that incorporates Solder Mask
> Defined (SMD) and Non Solder Mask Defined (NSMD) BGA pads on the same part.
> Solderable area on the pad is the same for both as is the solder ball
> diameter to place.  I'm concerned about coplanarity, but I don't have any
> data to back it up.  I know the SMD balls will be higher off the substrate
> than the NSMD balls, but by how much?  The reason for this design is
> electrical performance.
>
>         What do you think?  Is the amount of variation in height too small
> to be concerned about?
>
> Thanks,
>
> Glenn
>



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