Glenn,
 I don't think the difference is going to be significant enough, assumming
they are eutectic solder spheres. What needs to be considered is
reliability. Motorola did a study in 1996 which indicated that NSMD pads
were significantly more reliable.

Regards,
Rey Sosa
Pentagon EMS

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Glenn Pelkey
Sent: Tuesday, October 29, 2002 10:48 AM
To: [log in to unmask]
Subject: [TN] SMD and NSMD pads on same BGA


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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