I have a customer that objects to solder smear. "What" you ask, "exactly is
solder smear?" Subsequent to HASL, opportunities exist for boards to come
into contact with one another. One example of this would be NC fabrication
where panels are stacked and routed. During this contact, the solder features
on one panel may transfer solder to the solder mask on adjacent parts . This
happens more frequently when there is a high topography soldermask such as
SR1000. With low topography masks (LPI) the condition is nonexistent (at
least to the un-aided eye)

The objection stems from the notion that solder smeared (and we are talking
about an extremely low level, barley detectable with XRF) between traces
and/or pads creates a spacing violation, causing a potential bridging
condition. I have managed to convince the customer to accept this condition
at least on the solder side, reasoning that the smear will be removed during
wave. They will not, however, accept it on the component side.

I would be most interested in hearing from anyone with experience with this
condition. I have spoken with the very helpful folks at IPC about this issue.
It seems that there is no specification addressing this issue directly.

David Pizzoferrato
Centerline Circuits
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