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Our purchasing department requested the AT32UC3B1256 and the supplier has a few thousand in storage. However, those trays have a date code from 2009.

While shelf-life is normally not much of an issue with integrated circuits, 10 years is quite a number.

I looked for some general info regarding shelf-life. For example TI states:

[...] TI’s standard shelf life for packaged products is two years from the time it was manufactured to the time it is delivered by TI or a TI authorized distributor.

TI also offers extended shelf life (ESL) of certain products for up to five years of total shelf life from the time it is manufactured to the time it is delivered by TI or a TI authorized distributor Product warranty is measured from the actual shipment date, not the date of manufacture.

According to supplier, the trays are sealed. What would be the limiting factor for shelf-life with respect to micro controllers? May those parts require long tempering before assembly?

tl;dr: Should we be concerned about buying 10 year old micro controller?

In my opinion the shelf-life might be more limited by whoever wants to take the responsibility to guarantee that the ICs still work rather than that there are technical reasons for the ICs to "expire". So more a legal responsibility than a technical issue.

I think it is very likely that the ICs will just work without issue as they were stored in a proper way, in a dry environment.

If the price of these ICs was considerably less than "new" ones and your company is willing to accept that there might be a small chance that there are issues with these ICs then it can be a good deal.

If you prefer "no risk" and "guaranteed to work" then you might need to use "new" ICs.

You do not mention what the supplier states about the fact that these ICs are 10 years old, do they still guarantee 10 years lifetime for example?

The concern is solderability.

If not stored correctly oxidation on the pins can cause problems in the solder process.

Try ordering a few to begin with and see how it goes.

Your EMS might have some tricks to deal with components that have been on the shelf too long.

I would not worry too much about the chips functioning.

What I would be relatively concerned about is solderability- that’s the main reason behind the relatively short “shelf life” numbers. A more aggressive flux may help- there may be some recommended procedures used by low volume high-rel folks who may have little choice about using NOS parts. At the other extreme, I’m told one car maker has a 6-month limit on parts - reflecting the perceived risk of unreliable PCBs vs. their ability to dominate suppliers.

Also, if you are not 100% sure they were stored in a low humidity cabinet, a specified bake procedure is called for to drive moisture out of the plastic packages and prevent damage in the reflow process- it’s unnecessary for hand soldering.

Actually, I found an interesting document from TI: Component Reliability After Long Term Storage).

I will just quote some interesting parts here:

• Each year the semiconductor industry routes a significant volume of devices to recycling sites for no reliability or quality rationale beyond the fact that those devices were stored on a warehouse shelf for two years.


• Results show that current packaging material (mold compound and leadframe) is sufficiently robust to protect the active integrated circuits for many decades and permit standard reflow solder assembly beyond 15 years.


• Standard packing materials (bags, desiccant, and humidity cards) are robust for a 32
  month storage period that can be extended by repacking with fresh materials.


• Packing materials
  designed for long term storage are effective for more than five years.

Background:

• The origins of date code age restrictions are not well documented, but it is probable that limitations of the packing materials for moisture sensitive components and post storage solderability of SnPb or Sn finishes contributed to the
  concerns of customers that led to the shelf life restrictions

Device risks:

• Device functionality and parametric performance after extended periods of shelf
  storage
  
  
  
  
  • No failure mechanisms have been identified that would compromise the electrical performance or circuit reliability of LTS devices.
  
  
  
  


• Exposure to the ambient atmosphere for extended periods of time may oxidize the lead
  surface impacting solder wetting during assembly.
  
  
  
  
  • Aging studies have shown that NiPdAu lead finish devices pass solderability requirements beyond 8 years. Actual testing of LTS devices indicates that storage for 15
    years does not compromise solderability.
  
  
  
  


• Moisture absorbed in the epoxy matrix of devices categorized as MSL 2 to 6 could
  vaporize during reflow solder assembly and crack the package.
  
  
  
  
  • Devices targeted for LTS are packed in special metallized bags that are sealed with desiccant and a HIC.
  
  
  
  


• Devices stored for extended periods may exhibit corrosion of bond pads or interconnect
  metallization


• Devices that incorporate non-volatile memory may suffer data retention issues after long storage intervals.

Packing material risks:

• The static dissipative properties of tubes or tape and reel may degrade over time
  resulting in potential ESD damage to LTS devices


• Storage bags may leak, allow moisture to enter, and cause problems for MSL


• Label adhesives may fail or the ink marking could fade making lot history or device identification difficul

Conclusion:

The shelf life of LTS devices as determined by solderability, SEM visual, SEM spectral analysis, optical microscopy, MSL performance, solderability, and decapsulation/visual is >15 years.

IC packing material shelf life is limited by moisture diffusion through the MBB. A standard MBB maintains satisfactory moisture levels for 32 months. LTS bags control moisture levels
beyond 5 years.

Terms:

• Humidity Indicator Card: (HIC) – A card printed with a moisture sensitive chemical (cobalt chloride) that changes from blue to pink in the presence of water vapor.


• Long Term Storage: (LTS) – Storage of devices in an uncontrolled indoor environment for
  more than two years.


• Moisture Barrier Bag: (MBB) – Storage bag manufactured with a flexible laminated vapor
  barrier film that restricts transmission of water vapor.