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February 2002

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From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 20 Feb 2002 08:59:37 -0500
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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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