Hi Clayton & All -
There are no mechanical tests afforded the inspectors of
assembled electronic product, nor have there ever been. Simply put, the
product of an intentional mechanical movement of a soldered electronic
connection produces a change in the metallurgical structure of the connection
which cannot be measured or quantified as to its affects. Specifically,
this applies to idiots "using tweezers and wiggling it back and
forth".
Mechanical tests of soldered connections such as tensile,
shear, etc., are reserved for the collection of engineering data from test
specimen, not deliverable product. This data, in turn, is generally
converted to knowledge regarding acceptability of both design and manufacturing
practices. Note that when a set of requirements is finally published in a
design or manufacturing standard, that allowances have been given for safety
factors, so that that requirement is not easily compromised.
I've encountered a number of folks like the customer inspector
you described. The only way I've ever been successrul in correcting the
problems they create is by going back to the basic specifications governing that
particular contract s workmanship and inspection. This generally takes a
hard nosed approach and the support of your management.
At this stage, it sounds as if your customer owes you for the
time spent to deal with a product which he/she damaged thru use of an improper
test method.
Regards - Kelly
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