I posted a question a couple months ago about solderballs.  The debate
is still happening here.  I thought I would post a more specific
question regarding how to interpret the standards.
Consider a low voltage situation, where minimum electrical clearance is
0.13mm according to Table 6-1 in IPC-2221. 
IPC-A-610 states for acceptable:  Solderballs are entrapped/encapsulated
and do not violate minimum electrical clearance.
Components are so small now, that solder fines are starting to come into
question when they would probably have never been noticed a few years
ago.
If a solderball is entrapped under a component between two pads, and the
sum of the distance from pad to ball and ball to next pad is greater
than 0.13mm, but each individual distance (pad to ball) is less than
0.13mm - does this violate minimum electrical clearance?
The solderball is not connected to anything.
My thought this is a violation, because the solderball is sort of like a
stepping stone in the middle of the stream, that would make arcing that
much easier.  But I am wondering if my logic is flawed?  An arc still
needs to cover the whole span, and the solder ball isn't electrically
connected or contributing to the voltage difference
.
These are usually solder fines that aren't moving.  If one were to
somehow get loose and move toward one pad, though, the remaining
distance would not be a failure.  It is just when they are trapped in
the middle between two pads that each individual distance is a failure.
If the stepping stone idea is correct, we have a lot of solder fines to
rework.  So I am hoping it is incorrect...  But we will do what is
right.

Your assistance in interpreting the standards is much appreciated.

Genny 

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