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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