I nice discussion thread on this, but don't forget about minimum electrical clearance.  IPC-2221 Table 6-1 is the industry standard for spacing between non-common conductors.  It's used by designers who (hopefully) include some guard area to allow for process variables (placement, coplanarity, ball collapse, solder quantity variables).  There's probably a bit more consideration needed than just "doesn't short".  Jack

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>>> [log in to unmask] 04/17/01 07:32AM >>>
Hi Steve,

Sorry if I didn't present the question clearly.  The question I am asking is refer to the
spacing (gap) between two solder joints not the pitch of a BGA component.  For example, in a
1.27mm (50 mil) pitch BGA, a solder joint is roughly 35 mil after reflow, that leave the
theoretical spacing between the solder joints become 15 mil.  However for some reason the
package that used may have balls that off the true position which may result the two solder
joints come very close together after reflow.

What would be the minimum allowable spacing between the two joints?

Thanks,
Alex