I've been given the task of verifying a batch of ICs from a chinese broker, to see that the chips the company has bought are what the broker claims they are. The package we've received looks like this, and has this statement (amongst others) on it:
Why is this recommendation given? The shelf life of the ICs has to be much greater than 5 days right? And how critical is it for me to follow this statement?
The parts can survive well beyond 5 days. However, the component is moisture sensitive. And if you don't store it well (in a well-controlled environment), it could cause SMT assembly issues such as dry soldering.
There are other methods that you can use if you have to use if after a prolonged period post opening the package to reduce such assembly issues. A common method is to do baking where you keep the component in a special oven at a set temperature for a certain duration. Temperature and duration depend on components. This can reduce the number of failures during mass manufacturing.
If you want to use it for prototyping using manual soldering, the impact will be less but if you are planning to use such components for mass manufacturing at an EMS, then better to consume fast once the package has been opened.
It's to do with Moisture sensitivity. When the components were packaged, there were done so in a controlled environment, particularly with regard to humidity (or lack thereof, you can see that bag was packaged at 20% which is pretty low). When you open the bag, the components are exposed to the humidity of your working area (which varies a lot, but my UK house is usually 50-70%), which probably isn't controlled to the same level.
Once this has happened, moisture gradually begins to enter the device, from the atmosphere. When you then assemble the boards,if you use an oven the package will be exposed to 200+ degrees, hand soldering presents much less of a risk. If excess moisture has entered the device, this change in temperature can cause damage as the moisture expands.
One mitigation is to simply bake the parts at a lower temperature prior to assembly to gradually remove the moisture.
I expect the original manufacturer should provide MSL Ratings and Reflow Profiles. See https://www.ti.com/lit/an/spraby1a/spraby1a.pdf as an example from Texas Instruments which:
This application reports explains the relationship of MSL rating to the customer production floor life and surface mount reflow temperatures for TI semiconductors.
65Roadster has already provided a reference to J-STD-033 for helpful background and information.
The above TI application report also references:
STD-020D.1: Joint IPC/JEDEC standard for moisture and reflow sensitivity classification for nonhermetic solid state surface-mount devices
