Stan,

The glue upon curing does become brittle.  However, unless the warpage
was extra-ordinarily severe, I cannot see that to be the cause.  Was the
boards cured properly accordance with the manufacturer?


Tom Han
Ardent Systems

On Wed, 7 Oct 1998 14:16:00 PDT "Traxler, Stan"
<[log in to unmask]> writes:
>We recently had a small lot of pwa's (qty 3),where a large quantity of
>the
>SMT chips on the backside of the boards (approximately 60 on each
>board)
>came off during the wave solder process. It appears that the glue
>failed
>during some stress, (not a poor bond line), when viewing the "failed"
>locations,(within the same glue dot) some of the glue stayed on the
>board
>and some came off with the part. (Also the glue dot size was adequate)
>
> The boards are  mixed technology boards where all the thru-hole
>components
>are assembled to the top side of the board, then the SMT components
>(chip
>capacitors, mainly 1210's) are glued to the back side of the board
>using
>Loctite 348 and the glue is cured in an inline oven.
>
>We ran 3 other lots (similar designs) the same morning, using the same
>glue,
>and the same process, with no part loss. (also this board has been run
>in
>the past without these failures) The only visible difference between
>these
>boards and the other 3 lots is they appear more warped.
>
> I'm wondering if when loading the board onto the wave solder fingers
>(removing the warp that was on the board) could this have caused the
>glue to
>crack and weaken to a point where they could have fallen off in the
>wave.
>(we did see the parts in the wave after the boards were processed).
>
>Has anyone out there had a similar experience or have some
>theories????
>
>
>Thanks.......
>Stan
>Raytheon
>Towson, Md
>
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