The current IPC/JEDEC standard J-STD-033 for moisture-sensitive devices does not include a bake cycle at 90C (it includes cycles at 40C and 125C for non-assembled components in reels or trays).
However, the upcoming revision, which should be released before the end of the year, includes a bake cycle at 90C for populated boards, mainly for hot air rework or second side reflow.
The bake duration at 90C, as with other bake temperatures, varies based on the specific components that must be baked, according to their MS level, body thickness and their level of moisture content (i.e. saturated or at limit of floor life). At 90C it ranges from 11 hours to 10 days. Take note that the 11 days is only valid for the best case condition, for a component with MS level of 2a, body thickness less than 1.4 mm and at the limit of floor life. (I can send you a copy of the proposed revision if you are interested).
In other words, the 12 hour bake cycle at 90C is really out of line with the industry standard. I suspect that it will be hard to convince any informed customer that this is a safe approach. Don't forget that a partial bake is sometimes worse than no bake at all because initially the ingressed moisture is being pushed towards the critical interface at the center of the package.
Internal defects such as partial cracks and delaminations cannot be detected with standard test and inspection tools but they will reduce the MTBF and increase the risk of early life failures.
Francois Monette Cogiscan Inc. Tel : 450-534-2644 fmonette@cogiscan.com
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