Don,
We investigated this same issue for Mil-Spec parts about two years ago.  Because
of our ultra-low volume, we tend to allow our parts to sit in stock for quite a
long time prior to use.

To summarize, we found that not all Mil-Spec, chip passives are tested for
solderability on a lot to lot basis.  Rather, a periodic sampling is performed
on some types of chips (e.g., every six months).  Secondly, we often times
purchase parts from distributers who have had the parts in their stock for some
time, with conditions which are pretty much unknown to us.  We polled various
manufacturers and were given times from six months to two years for shelf life
of pre-tinned terminations.

The actions that we took include assessing shelf life from the lot date code
(date of manufacture) and not the purchase or receiving date.  Establishing an
eighteen month shelf life, prior to a lot sampling test for solderability
(various locations on a reel proved to be impractical for us - right off the
top).  Initiating an end termination mechanical test.  It turns out that end
terminations are not tested for adhesion for the majority of passives we looked
at.  Lastly, it is considered the manufacturer's (internal or external)
responsibility to assess the solderability prior to assembly - manufacturing
risk.  This implies that even if the parts are within the shelf life, we
recommend that our internal labs sample the lots for solderability prior to
assembly.  Attrition quantities have been increased to allow for this type of
sampling.

Our ultra-low volume applications make it necessary/viable to perform some steps
which production facilities may not have to/be able to perform.  So please take
this info with that in mind.

Phillip Barela - Jet Propulsion Lab
_______________________________________________________________________________
Subject: Shelf Life of Pre-Tinned Leadless Components
From:    <[log in to unmask]> at Internet
Date:    5/9/95  7:23 AM

Does anyone have any information regarding the shelf life of leadless
pre-tinned components(chip caps and resistors, LCC packages)?

First, what is the shelf life for these components when stored without
significant precautions (ie. stored in orginal packaging, 20 to 50% R
humidty and temperature 72 +/- 10 degrees).?

What is the recommended storage to enhance shelf life? ie controlled
temperature humidity etc. and do you have data on how long the shelf life
can be increased.

How does one go about testing shelf life for components packaged on a reel?

By testing the first components on the reel does that give a good indication
of the parts in the end of the reel?


Thanks
Dan Krebs
AlliedSignal Aerospace