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March 2, 2018

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 thesesettings be different from typical short term storage?

R.A.

Expert Panel Responses

It has been our experience that dry cabinetsthat hold 25 C at 0% RH with or without nitrogen work well for long termsolderability storage if they are solderable going in.

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Terry Munson
President/Senior Technical Consultant
Foresite
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.

Mostall manufactures ship their products having a Moisture Sensitivity Level (MSL)> 1 in a Moisture Barrier Bag (MMB) containing a desiccant to keep thehumidity near zero and a Humidity Indicator Card (HIC) to prove it. This sealedMMB is only good for a year, unless the manufacture says otherwise. Sothe best environment to keep components, according to J-STD-033 for longperiods of time is in the same basic conditions as a MMB: <5%RH. This is thebest way to stop moisture absorption, contact corrosion, and prevent the needto bake the parts before use. The only other issue is proving that these conditions were indeedmaintained for the entire 10 years! This is where a good RH and Temperaturemonitoring system of the storage environment is critical to prove conformanceto J-STD-033. Check out the SensorWATCH system on line, a system designed to doexactly this: monitor the RH and Temperature in the manufacturing and storageareas of electronic assembly facilities. Without data to show conformance tothe required RH levels in your storage system, you are forced to bake the partsbefore use, which can add to corrosion and possible component damage.

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Paul Austen
Senior Project Engineer
Electronic Controls Design Inc
Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.

As an Aerospace & Defense OEM, we have the samerequirements, and have implemented LTS (Long-Term Storage) protocols to dealwith it. Following are the risks that require mitigation for electroniccomponents:
  1. Oxidationof lead finishes destroys solderability
  2. IMC(Intermetallic Compound) growth through to the surface destroys solderability
  3. Moistureuptake requires pre-bake, which will incur additional risk per (1) and (2)
Mitigation of risks (1) and (3) can be accomplished by excludingoxygen and moisture. A nitrogen-purged, sealed MBB (Moisture barrier Bag) withthe proper amount of desiccant enclosed per J-STD-033 will be good forapproximately three years. The time depends entirely on the quality of the bag(permeability) and the quality of the seal. Rather than re-package atintervals, storing the MBBs within a dry, nitrogen-purged cabinet will allowyou to maintain the dry, oxygen-free environment within the MBBs indefinitely. Mitigation of risk (2) is not accomplished by excludingoxygen and/or moisture. The only way to slow the growth of IMCs is to storeparts at cold temperatures, but this is not recommended. Most good componentfinishes, when held at 20C, should not degrade to the point of losingsolderability over a 10-year period.

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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

My first question wouldbe "why do you need to store components for 10 years". I am going toassume that this is for a user requirement but given the state of obsolescencethis seems to be a long timeThe proper method forlong term storage of devices would be as follow
  1. Make sure thesedevices are as moisture free as possible, dry box storage, before packaging.
  2. Utilize a properlysized MVB, Moisture Vapor Barrier bag, Do not scrimp on the side of costs. Usea top quality bag. Use the thickest bag you can get. 6.5 mil would berecommended.
  3. Use a vacuum sealerthat has a N 2 purge, critical to remove as much O 2 as possible.
  4. Use a desiccant packappropriate to the size of the total volume of the devices being packaged.
  5. Insert amoisture/humidity card to detect if a breach has occurred. Verify that thecard can be read after sealing.
  6. Vacuum at the highestpossible draw you can attain.
  7. Heat seal.
  8. Verify seal.


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Jerry Karp
President
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.

Preservation of solderabilityfor such a long period of time would involve mitigating the two main reasonsfor deterioration of coatings. Oxidation or corrosion of the surface finish canbe minimized by storing in nitrogen or, alternatively, in a sealed moistureproof bag. Diffusion and intermetallic growth between coatings and substratescan also cause solderability issues and is accelerated with temperature andtime. Storage at a low temperature would therefore be an advantage. Perhaps acombination of low temperature storage within a moisture proof sealed bag wouldbe the preferred option.

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Bryan Kerr
Principal Engineer - CMA Lab
BAE Systems
Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.

Storing ofcomponents for a long period of time is based upon the requirements ofJ-Std-033C. This documentspecifies the bake out times especially for SMT components, which are to beused after a storage period of time. Sect 5.3 Safe Storage, is define as meaning dry SMD packages held in a controlled humiditycondition such that the floor-life clock remains at zero. Acceptable safestorage conditions for SMD packages classified as Level 2 through 5a are listedbelow. 5.3.1 Dry Pack Drypacked SMD packages in intact MBBs, stored per 3.3, shall have acalculated shelf life of at least 12 monthsfrom the bag seal date shown on the caution or barcode label. 5.3.2 Shelf Life The minimum calculated shelf life is 12 months from bag seal date. Ifthe actual shelf life has exceeded 12 monthsbut less than 2 years from the bag seal date and thehumidity indicator card (HIC) (see 5.5.1) indicates that baking is notrequired, thenit is safe to reflow the components per the originalMSL rating. Although unanticipated, factors other than moisture sensitivitycouldaffect the total shelf life of components.Note: An HIC (Humidity Indicator Card) that has beencontinuously 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 bypurging with dry air or nitrogen at 25 +/- 5 C. Thecabinets must be capable of recovering to their statedhumidity rating within one hour from routine excursions such as dooropening/closing. 5.3.3.1 Dry Cabinet at 10% RH SMD packages not sealed in a MBB may be placed in adry atmosphere cabinet, maintained at notgreater than 10% RH. These dry cabinets should not beconsidered a MBB. Storage of SMD packages in these dry cabinets should belimited to a maximum time per Table 7-1. If the timelimit is exceeded they should be baked according to Table 4-2 to restore thefloorlife.5.3.3.2 Dry Cabinet at 5% RH SMD packages not sealed in a MBB may be placed in adry atmosphere cabinet, maintained at notgreaterthan 5% RH. Storage in these dry cabinets may be considered equivalent tostorage in a dry pack with unlimited shelf life. Therefore,5.3.3.2 infers that storage in an environment of less than 5% RH, may beconsidered to be stored in a dry pack with unlimited shelf life. It is importantto 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 layerdue to solid state diffusion and second through exposure to contamination beingdeposited on the surfaces of the component leads. Therefore it would beadvantageous to store the devices below 30C [86F].

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

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 oxidationbrought 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 solderabilityand reducing oxidation is critical. Oxidation can be reduced by using vacuumpacking or flushing with nitrogen before sealing in low permeation plastic bags. The plastic bags used should restrict bothair and moisture. As for the storage environment it should be free of oxidizingagents, free of sulfur containing cardboard, be low in humidity 20% or less and at room temperature or cooler in the range of 60-70F.

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Peter Biocca
Senior Market Development Engineer
Kester
Mr. Biocca was a chemist with many years experience in soldering technologies. He presented around the world in matters relating to process optimization and assembly. He was the author of many technical papers delivered globally. Mr. Biocca was a respected mentor in the electronics industry. He passed away in November, 2014.