|Ask the Experts|
June 3, 2021
Looking for Long-term Component Storage Options
Looking for long-term (10+ years) options to store components (IC's) in dry or nitrogen environment. Can you provide some options?
|Expert Panel Responses|
J-STD-033D, "Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices" offers three methods. Here is a brief summary:
1) Store in a Moisture barrier bag (MMB) with Humidity indicator card (HIC), per Section 3, and checking the HIC and resealing every 12 months, baking any components whose HIC show exposure due to failed MMB.
2) Store in a dry atmosphere cabinet purged with nitrogen at <=5%RH and temperatures 25+/-5C.
3) Store in a dry atmosphere cabinet purged dry air (desiccant) <=5%RH and temperatures 25+/-5C.
All of these methods have a cost, although most agree that a desiccant (dry air) driven Dry storage cabinet (#3) has the lowest overall cost to own and operate.
Senior Project Engineer
Electronic Controls Design Inc
10 years is a really long time. The main concern is deterioration of solderability. But if you do have to store, oxygen free environment, that means nitrogen environment for storage is a good option. It is better than just dry environment.
Ray Prasad Consultancy Group
10 years... Wow. Are these IC's in the original tubes? Hopefully they were provided in ESD compliant products.
From moisture perspective that device need to be sealed in MVB, moisture vapor barrier bags, under a vacuum seal. The thickest possible bag available. Reality is there is no way to draw a total vacuum on earth. Best recommendation IMO is thickest MVP bag possible, Max vacuum draw with nitrogen purge & a verifying check annually. Storing in an N2 dry box for 10 years will be expensive.
Storage of components for ten years or longer is generally not a normal practice since most components are consumed on a first-in, first-out basis unless one is building end-of-life products. If the components in question are in their original sealed packaging from the component manufacturer there should not be a problem with long-term storage providing the MSL is 3 or less.
If the original packaging has been opened it should be resealed in a moisture barrier bag together with a desiccant and a RH indicator card to indicate the RH remains below 5%, and they should be stored in a nitrogen dry cabinet.
As a precaution you should always double check with the component manufacturer as to their recommendations for long-term storage.
I generally do not like to disagree with the experts, but long-term storage requirements for legacy electronic components (and actually, for many mechanical parts and even certain materials) are actually quite common, and a 10-year preservation requirement is considered medium-term.15 years or longer is considered long-term. There are many, many high-reliability products that have a minimal downtime requirement, and they are either not easily replaced by newer models or are not cheap, or both. Some examples of this are train controls and train traffic controls, automotive traffic controls, military systems such as torpedoes, cruise missiles, missile silos, avionics control systems, naval ship electronics, certain hospital equipment such as c-scans, X-rays, etc.
It is very costly to replace an embedded system or a large ship simply because electronic components for those controls are obsolete. To save costs and ensure continuous run time, it is quite common to have a long-term storage requirement to handle not only after the sale service, but also very-long after the sale needs. Usually, these protective measures require only a good drypak including nitrogen-sealed moisture barrier bags with both a getter and a desiccant sealed inside the main bag, with smaller bags of the same parts similarly drypacked and sealed inside the main bag. This allow for opening the main bag to remove only a small quantity of parts without having to expose all of them, and then resealing in a new main bag with fresh desiccant and nitrogen purge. Then, to provide the triple redundancy required for some programs, the larger bags of compartmentalized components are placed inside a drybox, and not necessarily a nitrogen drybox.
Several papers have shown that this method will protect nearly all electronic components from any significant loss of solderability or reliability for longer than 15 years, with no nitrogen needed outside of the sealed bags. Some of these legacy contracts simply add a requirement that the drybox be held to at least -45 degrees C. for more stringent needs, as this is the only known method of ensuring no loss of solderability during LTS in these conditions. To complement this system, periodic solderability testing is also used, and this is where the compartmented smaller bags come into play, allowing a very small quantity of parts to be removed without compromising the rest.
But forget all about performing a meniscus wetting balance solderability test on these programs; most customers want solderability testing performed under actual production conditions using a scrap PWB and a 2-piece (or more) sample size of several different components to ensure solderability is being maintained.
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