I don't see what the pin length outside of the solder joint has to to
with the reliability of the solder connection, except as an indicator of
solder wetting inside of the hole. Above the solder fillet nothing is
achieved with respect to reliability.
For years the industry has installed PTH leaded components and
connectors and trimmed the leads to within a standard protrusion length
of .060" to .080" from the board surface (per 610). Anything less or
more requires a print note.
As long as the pin goes at least to the opposite side, and the hole fill
is a minimum of 100% (preferred), any additional length does nothing,
except possibly to provide leverage from an unwanted force. That would
be the opposite of what you are stating. 

When connector part numbers are selected one of the selection factors is
to avoid having to trim the leads.
Some of the circuit boards I work on are .125" thick, some even thicker.
There is no way I would ever leave pins sticking out 1/4" past the
bottom of the board if they are not needed for anything.
Using the .130" long pins with an .090" (actually, .093") PWB thickness
leaves about .037" protrusion. To me, that is ideal, provided there is
no fit interference. The portion of the pin that protrudes will form a
solder fillet. The wetting onto that fillet (or lack thereof) is the
indicator of the solder wetting taking place inside the hole.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Wednesday, September 05, 2007 11:18 AM
To: [log in to unmask]
Subject: [TN] Connector pin protrusion

Good Afternoon,

In reviewing PTH connectors it looks like the standard pin length (for
the through board connection) is double the board thickness.  For an
0.062 board the pins are 0.120" long and for a 0.090 board the pins are
0.180" long.  We have some connectors that have 0.130" long pins that we
want to use in an 0.090" thick board.  I maintain this shorter pin will
be problematic to solder reliably.

Am I on the right track?

Phil

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