What Is the Recommended Component Storage Environment?

Phil
Welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting, the Assembly Brothers. So what's today's question Jim?

Jim
Well it comes from G.H. What do you recommend as an environment for component storage to prohibit oxidation, relative humidity, nitrogen atmosphere, temperature, etc?

Is there a standard storage environment scenario considered as good practice?

Phil
With moisture sensitive devices, there are specifications.

JEDEC J-STD-020C
Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices

JEDEC J-STD-033C
Standard for Handling, Packaging,Shipping, and Use of Moisture/Reflow Sensitive Surface-Mount Devices

You definitely want to abide by those and that's absolutely best practices. We say that but not everybody does due diligence on those so take care of those MSD's and we've covered that on some other Board Talks.

But looking at run of the mill components, if they came in bags leave them sealed in the bags they came in until you're really ready to use them. Minimal exposure to ambient conditions. Obviously you can repackage them.

As far as in your storage area, relative humidity, temperature, nothing really special is needed.

Jim
You have to be conscious of any contaminants that are in the atmosphere that are going to affect solderability over the long term.

I think the most important thing is put them back in packages and seal them up reasonably well to prevent them from interacting with the environment. I want to point out that the standard against which for exposure that all MSD components are measured against is 30 C, 60% relative humidity.

You wouldn't want to go above that.

Again, you should be worried about contamination, any sulfur or other stuff that's in the air and avoid big swings in your storage condition so that you won't get condensation.

Put them back in the storage containers and seal them up. It's not necessary to vacuum seal like you do for MSD components, but reasonably well sealed when you're not using them. 

Phil
For best practices monitor and control relative humidity and temperature in your storage area. Beyond that, no, you normally don't necessarily have to put them in a dry box. 

Jim
The long-term solderability of any part at the highest level is determined by the quality of the surface finish that's on the leads. If they're good and well coated with whatever kind of plating they have.

Most parts are coming in today with tin over nickel. Make sure that that tin is put on properly because if it's not you're going to have problems long term no matter how you store them unless you go to the extreme of a nitrogen environment.

Phil
I hope we answered the question succinctly. You've been listening to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting, the Assembly Brothers.

No matter how you store your components and how solderable they are or may not be, when you go to solder them, don't solder 'em like my brother.

Jim
And don't solder like my brother. 

I, too, was surprised at the lack of mention of humidity indicator cards. In addition, there was no mention of adding a desiccant to the moisture barrier bag along with the devices.

Some years (1-3) storage within a metal laminated dry bag is not a problem for solderability if it is possible to avoid Sn/Cu migration with a Ni layer. What about 5 and more years for a customer specific chip layout? A recommendation is to store the wafer in a dry bag instead of the completely packed device.

This will allow you to change packaging type after years if you relayout your PCB to advanced packaging. An agreement with the chip manufacturer is recommended.

The question does not really have anything to do with MSDs and their pertinent standards mentioned, but is related. Long-term storage for what are called 'Legacy' programs is the subject being discussed here. Legacy products are certain products or programs (including chemicals, disposable, software and documentation) that require long-term spare components and spare assemblies because they are not easily replaced, cannot be down for long periods, or are either extremely large and costly. People's lives or major systems depend on them, and parts for these cannot be allowed to become obsolete.

Examples exist in every industrial field, including medical (C-scan equipment and peripherals, X-ray equipment, blood plasma equipment such as dialysis machines, etc), and traffic/train/transit control systems, avionics controls of all types both in the plane and in the air, traffic control systems, large excavators and other mining equipment, ships, submarines, military tanks, missiles, and weapons systems of all types needed for battle readiness, satellites, space shuttles and space stations and (soon to be) space colonization systems, and so on.

These all require spare parts and assemblies and software that cannot be allowed to become obsolete; a long-term buy-and-store system is required to keep them operable in some cases for as long as 30 to 50 years. This is different than the long-term reliability that is built-in to the product; everybody knows things wear out if used daily, and even missiles are periodically tested. A C-scan cannot simply be thrown away and replaced due to lack of components and/or assemblies or software or proper documentation. Legacy programs like these (and there are many!) require long-term storage practices for spares to ensure they remain viable, solderable, and reliable.

Legacy component packaging and storage is similar to MSD packaging and storage with the exceptions that the parts are individually bundled and sealed in smaller quantities inside of a larger bag that is in-turn sealed and stored, typically in a different form of drypak that uses replaceable vacuum valves in the storage bags. These valves are used to first apply an inert gas such as nitrogen but other gases are also used, as well as "getters" and other materials that not only prevent oxidation over time, but also prevent other parts of the components from aging over time as well.

Typically the packaging is performed, and then the entire bags are sealed inside refrigerated dry storage to -40 C. Simply removing oxygen is not enough, only deepfreeze PLUS proper inert storage will completely stop oxidation and other issues. There are different long-term storage methods for different types of components, assemblies, chemicals, software, and even documentation.

You are right when say that there is no need for special condition for the environment to store moisture sensitive components, but you need to remember that the sealed packing guarantee for the shelf life at low humidity for 1 year is if the storage temperature is <40 degrees C and relative humidity at <90%. So, you need keep the temperature and relative humidity at storage area below that.

By the way, the only indicator that can determine if you will need to bake the component when opened from the original packing is the Humidity Indicator Card, just like in J-STD-033 new version D, if its exposed time is exceeded.