|Ask the Experts|
November 3, 2020
Long Term Component Storage
We need to store a variety of electronic SMD components for at least 10 years.
What do you recommend for humidity and temperature settings?
Would these settings be different from typical short term storage?
|Expert Panel Responses|
It has been our experience that dry cabinets that hold 25°C at 0% RH with or without nitrogen work well for long-term solderability storage if they are solderable going in.
President/Senior Technical Consultant
Most all manufactures ship their products having a Moisture Sensitivity Level (MSL)> 1 in a Moisture Barrier Bag (MMB) containing a desiccant to keep the humidity near zero and a Humidity Indicator Card (HIC) to prove it. This sealed MMB is only good for a year, unless the manufacture says otherwise.
So the best environment to keep components, according to J-STD-033 for long periods of time is in the same basic conditions as a MMB: <5%RH. This is the best way to stop moisture absorption, contact corrosion, and prevent the need to bake the parts before use.
The only other issue is proving that these conditions were indeed maintained for the entire 10 years! This is where an RH and Temperature monitoring system of the storage environment is critical to prove conformance to J-STD-033. Without data to show conformance to the required RH levels in your storage system, you are forced to bake the parts before use, which can add to corrosion and possible component damage.
Senior Project Engineer
Electronic Controls Design Inc
As an Aerospace & Defense OEM, we have the same requirements, and have implemented LTS (Long-Term Storage) protocols to deal with it. Following are the risks that require mitigation for electronic components:
Mitigation of risk (2) is not accomplished by excluding oxygen and/or moisture. The only way to slow the growth of IMCs is to store parts at cold temperatures, but this is not recommended. Most good component finishes, when held at 20°C, should not degrade to the point of losing solderability over a 10-year period.
My first question would be "why do you need to store components for 10 years". I am going to assume that this is for a user requirement but given the state of obsolescence this seems to be a long time.
The proper method for long term storage of devices would be as follow
Preservation of solderability for such a long period of time would involve mitigating the two main reasons for deterioration of coatings. Oxidation or corrosion of the surface finish can be minimized by storing in nitrogen or, alternatively, in a sealed moisture proof bag.
Diffusion and intermetallic growth between coatings and substrates can also cause solderability issues and is accelerated with temperature and time. Storage at a low temperature would therefore be an advantage. Perhaps a combination of low temperature storage within a moisture proof sealed bag would be the preferred option.
Principal Engineer - CMA Lab
Storing of components for a long period of time is based upon the requirements of J-Std-033°C.
This document specifies the bake out times especially for SMT components, which are to be used after a storage period of time.
Sect 5.3 Safe Storage, is define as meaning dry SMD packages held in a controlled humidity condition such that the floor-life clock remains at zero. Acceptable safe storage conditions for SMD packages classified as Level 2 through 5a are listed below.
5.3.1 Dry Pack
Dry packed SMD packages in intact MBBs, stored per 3.3, shall have a calculated shelf life of at least 12 months from the bag seal date shown on the caution or bar code label.
5.3.2 Shelf Life
The minimum calculated shelf life is 12 months from bag seal date. If the actual shelf life has exceeded 12 months but less than 2 years from the bag seal date 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 (Humidity Indicator Card) that has been continuously sealed in the MBB is typically accurate for a minimum of 2 years.
5.3.3 Dry Atmosphere Cabinet
Storage cabinets which maintain low humidity by purging with dry air or nitrogen at 25 +/- 5 C. The cabinets must be capable of recovering to their stated humidity rating within one hour from routine excursions such as door opening/closing.
18.104.22.168 Dry Cabinet at 10% RH
SMD packages not sealed in a MBB may be placed in a dry atmosphere cabinet, maintained at not greater than 10% RH. These dry cabinets should not be considered a MBB. Storage of SMD packages in these dry cabinets should be limited to a maximum time per Table 7-1. If the time limit is exceeded they should be baked according to Table 4-2 to restore the floor life. 22.214.171.124 Dry Cabinet at 5% RH SMD packages not sealed in a MBB may be placed in a dry atmosphere cabinet, maintained at not greater than 5% RH. Storage in these dry cabinets may be considered equivalent to storage in a dry pack with unlimited shelf life.
Therefore, 126.96.36.199 infers that storage in an environment of less than 5% RH, may be considered to be stored in a dry pack with unlimited shelf life.
It is important to remember however that this is for moisture entrapment within the component. We must also be concern with the solderability of the component leads which maybe impacted by two elements, one being the growth of the intermetallic layer due to solid state diffusion and second through exposure to contamination being deposited on the surfaces of the component leads. Therefore it would be advantageous to store the devices below 30°C [86F].
Vice President, Technical Director
The key is to preserve solderability and keep moisture out.While removing moisture is relatively easy by doing a bake oxide,increases in oxidation are harder to deal with. Higher oxidation brought on by exposure to air for many years may later require the use of more active flux systems.
In some cases using a stronger flux is not allowed. So preserving solderability and reducing oxidation is critical. Oxidation can be reduced by using vacuum packing or flushing with nitrogen before sealing in low permeation plastic bags. The plastic bags used should restrict both air and moisture.
As for the storage environment it should be free of oxidizing agents, free of sulfur containing cardboard, be low in humidity 20% or less and at room temperature or cooler in the range of 60-70°F.
Senior Market Development Engineer
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