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I have a bag of DAC7512N digital to analog converter from TI. They are still sealed in the original packing, however the caution notes denote "calculated shelf life in sealed bag: 24 months" and the sealed date on the packing dates back to 01/01/07. Now the question is the shelf life an absolute lifetime for the devices in other words after the 24 months are the component unusable? or does it mean that at this point further procedures must be applied to the component such as baking before they could be used in a circuit?

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The concern is that moisture may enter the device package. When the "moist" package is heated during reflow soldering, that moisture could turn to steam, and damage the package as it expands. If you will be mounting the parts using reflow soldering (or otherwise heating to near solder temperature) they should be baked gently first, to dry them.

The functionality of the parts should not be affected.

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The minimum calculated shelf life is 12 months from bag seal date. If the actual shelf life has exceeded 12 months and the humidity indicator card (HIC) (see 5.5.1) indicates that baking is not required, then it is safe to reflow the components per the original MSL rating. Although unanticipated, factors other than moisture sensitivity could affect the total shelf life of components. Note: An HIC that has been continuously sealed in the MBB is typically accurate up to five years.

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