Has anyone heard of or done studies of toe-down lead configurations? We had an
instance today of a QA person asking of my opinion on a board that a high lead
count QFP that exhibited this problem. The foot of the lead was not parallel
with the pad and the end of the toe was the only part of the lead touching pad.
I started brainstorming and even asked my 'brother' Steve Gregory here about it.
He had heard of nothing.
My question is: Can the toe-down lead be more structurally sound than the normal
foot-down lead? My thinking is that if the toe is down then more solder volume
accumulates under the foot and the heel has more volume as well. I'm thinking
that this would give the lead more "elasticity" during thermal cycling and
current vibration. Also, I've spoke before of vacuolar porosity and the toe-down
lead would diminish this if not completely eliminate it. If the foot had more
open area between it and the pad, then less flux entrapment within the paste
would occur, letting it outgas normally.

Someone please tell me if my thinking is garbled.

Jason Gregory
Production Supervisor
LaBarge Inc.
(918)459-2367
[log in to unmask]

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