Hi Doug,
We looked at some of these at the Lake before I left.  They were program
specific and accomplished through coordination with a nameless contractor.
As is often the case, the specific reports were not available for public
release.
As I recall there were many additional issues due to the rigidity of the
adhesive as opposed to solder which was more forgiving. One of the
significant issues was passive component fractures.  We eventually did
arrive at material that was better than others with meticulous process
controls, but as you said the acceptance criteria for coverage was based
upon the soldering standards (2K) - as a default not a bad idea - IMO. Hope
that make you feel better about your project.
I don't put too much faith in pull tests since we don't do much of that in
operation environments (pulling on components).
Looks like you have a another extensive DOE. Good luck
BTW  If you can share, I would really like to see this incorporated in 610
acceptability criteria.

Best regards,

Mel Parrish
Soldering Technology International Inc.
Madison, AL


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Doug Pauls
Sent: Tuesday, December 09, 2003 2:14 PM
To: [log in to unmask]
Subject: [TN] Adhesive strength vs overhang


Good afternoon all,

Internally, we are having discussions on the amount of allowable overhang
of passive SMT components (R and C).  Our specifications are based on
solder joint connections and the solder specifications are not in question.
We have an application where a silver filled adhesive is used to make the
connection between SMT metalization and mounting pad.  The solder joint
requirements were applied to these adhesive joints and I am wondering as to
the validity of this.  The adhesive is epoxy based and, in my mind, more
rigid than solder.  I think we are unnecessarily rejecting parts that are
acceptable.

So, before I go off and do a complex designed experiment, I thought I would
check with the Technet crowd first.  Do you know of any studies that show
the adhesive force (e.g. pull strength) vs. the degree of pad overhang?

Doug Pauls
Rockwell Collins

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