Hi Phil,
You write:
>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

1) If "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",
how can this be defined as having "made it thru the HALT testing"?
2) Who annointed this particular HALT test (duration, loading) to be
representative of the loading in use for anything representing the desired
life of this automotive electronics? There is a lot of testing going on that
is Highly Accelerated only in the sense that it does produce failures early,
but does NOT accelerate the damage mechanisms at work in actual product.
3)  There are a lot of single-sided CEM-1 unsupported through-hole assemblies
produced today [it is cheap]; it is not surprising that these fail in the
automotive under the hood environment which is the most severe common use
environment by far.

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