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March 2000

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Subject:
From:
"Keel, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 20 Mar 2000 17:01:58 -0800
Content-Type:
text/plain
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text/plain (123 lines)
You know you are right.
This looks like a good example of
A less than optimal part being selected;
The mfg guys make it work good. (no failures)
New guys show up and say,
"You guys aren't doing it like that are you ? ?"
"It's really not necessary."
So methods are changed to reflect "current policy".
Then  --  wait for it  . . .
The failures show up in the field and we start the process all over again.
What a fantastic revenue enhancement tool.
Planned Failure Mode
Good luck Phil
I have the feeling you have been around this block before.



                -----Original Message-----
                From:   phil bavaro [mailto:[log in to unmask]]
                Sent:   Monday, March 20, 2000 10:05 PM
                To:     [log in to unmask]
                Subject:        [TN] Electrolytic Capacitor Staking
Requirements

                OK, I know, I know. Why is anyone still using thru hole
parts which have to
                be bonded to the board......!!

                Well. all I can say is that we are and the question I have
for this group
                is what are the requirements for how much and how high.

                Here's the background info:

                An automotive electronics circuit card has about seven very
tall
                electrolytic caps on it which need to be secured to the
board so that the
                vibration does not sever the two leads on these parts.
Historically I have
                always asked that these be bonded 360 degrees around the
perimeter and a
                minimum of 50%, up to a maximum of 100% of the height of the
part using a
                thixotropic UV cure adhesive.  This way the part could not
bend or move at
                all.

                Using this criteria, I have never seen a failure as a result
of the bonding.

                Here's the problem:

                A new engineer decides to minimize the adhesive amount (due
to cycle time
                of course) so that just it connects the board and the bottom
of the part
                only (maybe as high as .15" total which only allows about
.10" of contact
                to the body of the part.  These parts are .75" tall.  The
new engineer
                feels justified because the products which were bonded this
way made it
                thru a HALT test exposure without electrical failures.

                I look at the assemblies which are supposedly OK and find
that the adhesive
                has broken loose from the pwb on at least five out of the
seven parts and
                what is remaining on the parts have fracture lines as well.

                I consider this condition unacceptable and feel that after
environmental
                testing, adhesive bonding should remain intact 100%.

                Am I right or should I yield since the assemblies made it
thru the HALT
                testing?  What bonding requirements do you impose for these
type of parts

                All comments are welcome.


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