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Paul
Just a couple of remarks:
1. if the die bond is failing, then this is a component manufacturing
issue. This should not happen, even if the component is letting water
in.
2. if you are using 63/37, 260°C seems to me excessive. I would up the
preheat to, say, 110°C topside to make sure all the water in the flux
solvent has evaporated, including what has gone through to the topside
and reduce the wave temp to, say, 240 - 245°C (less thermal shock). You
may need to adjust the conveyor speed slightly, as well.
Brian
Paul Truit wrote:
>
> We are experiencing a problem related to an Optocoupler. I wanted to
> see if anyone had any ideas as to the whys. The IC's have failed
> intermittently in the field.
>
> Specifics:
> Mixed technology board. The Opto in question is Through Hole. It is
> Hand inserted. The board is processed using a VOC free OA flux that is
> sprayed on with a spray fluxer. 2 bottom side convection pre-heaters
> bring the board up to a 96°C (204°F) top side board temperature on a
> conveyor that is set for 4'/min in a wave solder machine. Wave solder
> pot is at 260°C (500°F). The maximum part lead temperature is
> 164°C(327°F) for 6 seconds. The board transitions into an aqueous
> cleaner. The board has 6 feet to cool off before hitting the water.
> This is 1.43 minutes. The water temp is set for 63°C(145°F). and the
> belt speed is set for 4'/ min. 2 dryer sections dry the boards off.
> Cooling of the part is a slope of -1.63°C/sec(-35°F/sec).
>
> The optocoupler's pass a functional test. They then fail intermittently
> in the field. Failure analysis of the IC has shown an inadequate die
> bond between the Lead frame and the silicon die. 2 different date codes
> have been found to have failed.
>
> There has been a different EMS making a similar board using identical
> part numbers that these boards have not failed. What appears to be
> different is we clean, they don't. Any issues with aqueous cleaning and
> Opto's? And this process causing the lead frame and die separation
> issue?
>
> --
> Paul Truit, Mfg. Eng.
> RBB Systems, Inc.
> 4265C E. Lincolnway
> Wooster, OH 44691
> Ph. (330) 567-2906 ext 514
> Fax (330) 263-5324
> Email: [log in to unmask]
>
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