Over the last 15 years there has been an explosion in the availability of
surface mount board-to-board connections. Some of these use traditional
folded pins, but more and more are using stamped pins with no stress
limiting bends in the connection.

Photo 8-181 in IPC-A-610H Section 8.4 is an example of this.

Can someone explain to me why IPC calls these "special" as opposed to what
they are: butt joints? I have a module supplier who claims the butt joint
requirements don't apply because they are "special". Thus, whereas butt
joints are dis-allowed in Class 3 and must not overhang the pad for Class
2, this module supplier claims they are fine. No doubt the "butt joint"
section of 610 should be updated to explicitly show this type of
termination, but anyone who categorizes soldered interconnects would have
to label these as common butt joints (where the metal is sheared out of
whatever stock it is made from and then soldered with the sheared side
against the pad.

If there were only a few of these types of connectors on the market, or if
they were seldom used, the "special" would be a valid term. But today
industrial PCBAs I see more commonly have these than not.

(And yes, a supplier who uses the "special" clause still isn't out of the
"hot seat" because they are supposed to bring this up with the customer
when they accept the job.)

By the way, another photograph in Section 8.4, 8-180, shows a standard
surface mount dual row header (which is made up of pins bent into an "L"
shape) with a surface mount to through hole adapter installed. What makes
that "special"? The fact it has something plugged into it? So if it leaves
the assembly plant without that adapter installed, it wouldn't become
"special" until a user plugged in that adapter socket?

Thanks!

Wayne Thayer