Long Term Component Storage

Phil
And welcome to Board Talk with Jim Hall and Phil Zarrow, pick and place, the placement brothers, the Assembly Brothers. What's our question today?

Jim
It comes from listener R.A. We need to store a variety of electronic SMD components for at least 10 years. What do you recommend for a humidity and temperature settings? Would these settings be different from typical short-term storage?  

Phil
You don't make life easier on yourself, do you RA?  

Jim
We know these people Phil. We have dealt with them. These are people who want to get lifetime buys of components that are going out of stock or becoming obsolete and you have to deal with them.

Of course the most critical concerns are if these components are moisture sensitive and you receive them in their nicely sealed moisture barrier bags which have their desiccant inside and the temperature humidity indicator card.  But if we read IPC/JEDEC standards 033.

They will see the moisture barrier bag is technically only guaranteed for a year.  Most people have not had problems storing longer than a year, but the question they certainly raised, do you want to keep them in a moisture barrier bag for 10 years.

One alternative that we have known people to address this issue with moisture sensitive parts is to immediately remove them from the moisture barrier bag and put them in a dry cabinet with humidity less than 5% which is the standard storage conditions.

Then monitor the humidity level in the storage cabinet continuously so that if anything should ever fail you have a record of it.

With other components which are not moisture sensitive you have to be concerned about at least the solderability of the terminations.

And in that case having a relative low humidity, certainly not 5% but and a reasonable temperature would seem to make sense.

Phil
Remember every time you re-bake these components if you indeed, indulge in that, you are going to probably have an effect on the solderablity of leads, depending on the finish.

Jim
Another strategy, a much cheaper strategy, with MSD components is just store them in normal temperature, humidity and bake them before you use them.  

But again, as my brother wisely points out, baking them always raises issues with the solderability.

And certainly in any case protect your components from any kind of atmosphere contaminants. Temperature and humidity are probably somewhat contributory although especially humidity for moisture sensitive components but any sulfur in the air or any other kinds of materials that could react with the surface finishes and degrade the solderability after 10 years.

Phil
Well, there you go, good luck. We are the Assembly Brothers and whatever you do --  

Jim
Don't solder like my brother.

Phil
Don't solder like my brother.

As Jim mentioned above moisture bags and baking components are not sufficient while struggling long term storage. Dry cabinet offers best solution for long term storage of SMDs besides it is the most economical and practical way in the long run without requiring labour or consumables. SMD components in dry cabinet are protected from any kind of materials in the air that could react with the surface finishes. Components permanently stored in dry cabinet do not require baking thus solderability issues do not arise. Dry cabinet offers a controlled environment for SMDs. Most critical point for dry cabinets is humidity levels and high precision.

We recommend LTS in nitrogen to our customers. Our storage cabinets run at constant 20 % 4.8 RH. We also recommend set aside a test batch from same date code for periodical testing IE: solder ability & diagonal cut section of leads/pins for any whisker growth checked via SEM. We have stock dating back over 10 years & 100% success rate!

There are companies specialized in long-term storage. There are also companies specialized in re-plating the pins. So you can go external.

Moisture may be an issue for larger parts, that is why it must be stored in a controlled environment with < 5% moisture.

Oxidation may be an issue. Parts can be stored in Nitrogen or vacuum to prevent this.

Tin pest may be an issue, that is a white powder on the pins. Do not stored at very low temperatures, or do and later replate the pins.

Internally, so inside parts, there may be issues. Migration on metals degrade leakage, noise etc. Store the parts at a low temperature to slow this down. Good parts designed by people who know what they do migrate less.

Outgassing (well know to me as we also build (aerospace components) is evaporation of carbons etc from plastic and epoxy packages. This gives a thin but nasty layer on metals and can pollute relay and connector contacts and probably solderability too. Ceramic components do not have this issue. Best is if you store in nitrogen to slowly replace the nitrogen so carbons do not build up too much.

Gold plated parts can be stored for a longer time, but the plating of the parts is important. There must be a good barrier layer between the Copper and Gold otherwise the Copper will migrate to the surface and oxidize. If it does, replating or using aggressive flux (cleaning!) will help, treat them as if they are just Copper pins.

Solderability performance of components are affected by oxidation under the storage environment. Possibly in one year time period. I would like to invite your comments as to how such large size of mass packaging unit as emboss carrier taping reels should be stored properly to extend their solderability performance as well as minimizing oxidation.

I came across this issue about 25 years ago for micro-circuits which were being declared as "Life Time Buys" and no longer being manufactured. After performing a few experimental samples and conferring with known solder experts, I came up with the following solution that worked extremely well.

The subject component leads were re-tinned to guarantee initial solderability. After cleaning thoroughly and assuring dryness, the components were immersed into jars of Vaseline. Solderability samples were taken initially at a 6 month frequency, then at a yearly frequency. All samples soldered like new. The Vaseline was easily removed using standard cleaning solutions. This method was simple, required no special equipment and quite cost effective.

JEDEC released a publication just over a year ago regarding this topic, JEP160 - Long-Term Storage for Electronic Solid-State Wafers, Dice, and Devices. It is a good reference document.