----- Original Message -----
Sent: Thursday, March 09, 2000 4:22
PM
Subject: [TN] Mechanical Straining Solder
Joints
Hi
TechNet
Has anyone got any
opinions on verifying solder joint quality by applying mechanical
strain?
I have had a board
rejected recently for "insufficient solder" on a corner pin of a wave soldered
SO08 package.
The joint was
inspected by Customer QC, who determined the joint was suspect due to dull
colour and potential insufficient toe fillet. To verify if the joint was
good or bad, mechanical strain was applied to the lead using tweezers and
wiggling it back and forth. This caused the lead to pull from the solder
joint. Leaving a pocket of solder on the pad from where the lead was
pulled (What was left of the pocket exhibited good heel fillet and sufficient
toe fillet).
Customer QC opinion
is that if a solder joint is good you should not be able to pull the lead from
the joint and if too much force is applied the pad will pull from the board
not the lead from the joint.
My understanding is
that a solder joint is not meant for mechanical strain only good electrical
contact therefore by applying force even a good joint will deteriorate.
Therefore, even if the lead doesn't pull from the joint, the quality of the
joint has been affected.
Any comments?
Would anyone classify this as a valid verification technique? How do you
verify a suspect joint?
Thanks
Clayton
Gardner
Engineering Manager