Guy,
The obvious answer is that modern SMT parts are totally different animals than those of past decades.
Even the U.S. Army has major concerns about long term storage of modern components and circuitry.
David A. Douthit
Manager
LoCan LLC
Guy Ramsey wrote:
> I was surprised by Peter's response to your post. I wonder what he means by
> exercised.
>
> I have work experience with manufactures of electronic instruments that are
> serviced for 50+ years (Been in business since just before W.W.II. In the
> early seventies they transitioned from analog to digital 27 V NMOS logic
> devices. They have components in storage from that time frame. There are
> occasional problems with lead frames that have failed (rusted under the
> gold) and occasional bad lots of die (didn't test everything before it was
> placed in storage). But, mostly, they are able to service and guarantee
> their work using solid state devices that were manufactured over 25 years
> ago. They use (stored in their own vaults or purchased through brokers)
> components that have been out of production for five to ten years; these
> would include Crowbar ICs, Switch-mode regulator ICs, Bucket-Brigade ICs, OP
> AMPs, Voltage Regulators and Transistors. I cannot recall getting bad (non
> functional) parts but we did have our soldering problems.
>
> Occasionally, there were differences in the performance of components that
> required changes to passive component values in some designs. We believed
> this was due to variation that was present at the time the components were
> made rather than related to changes over time.
>
> Relays or other Electro-mechanical devices are a concern (reed switches,
> motors, valves, solenoids). We had problems with them. But it would be hard
> to place a shelf life on them, are they hermetically sealed (many were to
> allow chemical cleaning)? Most of the problems I experienced were with open
> parts. Today many relays are open assuming no-clean processing.
>
> Electrolytic capacitors, carbon resistors are a concern but carbon resistors
> are really a thing of the past. SMT Electrolytic cans, five years would be a
> very conservative limit if you are talking about function.
>
> Solderabiltiy is your main concern Genny.
>
> Guy Ramsey
> Senior Technician / Instructor
> E-Mail: [log in to unmask] <mailto:[log in to unmask]>
> Ph: (610) 362-1200 x107
> Fax: (610) 362-1290
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Genny Gibbard
> > Sent: Tuesday, February 19, 2002 10:19 AM
> > To: [log in to unmask]
> > Subject: [TN] How old is old?
> >
> >
> > One of the purchasers has asked if they can purchase some parts
> > with a 2000
> > date code on them for 'a really great deal!' The part is an 8 lead uSOIC
> > package
> > At what point do you say they are too old?
> > I would appreciate info specific to this package or, just in general,
> > guidelines for chip or standard SM components. We do not use
> > BGA's yet. We
> > aren't trying to do lead free. We generally spec 60/40 HASL finish on our
> > boards.
> > Thanks for your time.
> >
> > Genny Gibbard (mailto:[log in to unmask])
> > Product Transition and Support
> >
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