Use with utmost caution if you have to. Solder joint strength varies enormously according to
rate of stress direction of stress and so on and are very poor in peel, which is most likely
what your guy has done.
There is tons of stuff on this in Technetpast.
Seeing as how your customer probably doesn't appreciate technical facts try an  analogy on him:
Sardine cans. These are supposed to be hermetically sealed or you die. Yet the lids can be
peeled off by hand so how can they be hermetic?

Mike Fenner


----- Original Message -----
From: Clayton Gardner <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 10, 2000 12:22 AM
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

A.E.M.S
11-13 Fiveways Boulevard
Keysborough VIC 3173
AUSTRALIA
Ph. 61 +3 9701 5499
Fx. 61 +3 9701 5422
Mb. 0416044552
Email:  [log in to unmask]
WEB:  www.aemspl.com.au

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