Leo, you said:

>The problem we are facing is that a customer is having us hold SMT
>devices for next years production.  We have some materials in storage
>for 6 months already and by the time the material is in use, some may be
>over one year.

Don't know about South Dakota, but here in Texas I solder parts every day
with date codes in 95 - sometimes 94 - with little difficulty. Holding
parts (which aren't already quite old) a year or so should not be a problem
if they are stored properly or haven't already been mistreated.

>In the past one customer who held material, for 15
>months and then found it was unsolderable, scrapped over $100,000 worth.

I think even WS-6536 permits the storage of parts for 12 months under
proper (i.e. low humidity) conditions. Are you using a flux/paste with any
guts at all? If not, call Alpha or Multicore or Kester and have them advise
you. I've always been a big believer in the power of chemistry, and a big
doubter of no-clean or other wimpy fluxes. Give me something that I KNOW
will reduce oxides.

>Has the IPC issued any guidelines for storage times?  Are there
>recommneded techniques such as vapor bags with dessicants or storage in
>inert gas environments, etc that are practical?

Don't know about IPC. My suggestions:

Make sure you have parts that are not already jeapordized by improper
storage or "old age". Check the date codes. Tell your customer you can't
guarantee it if you have doubts the parts aren't OK today.

Keep the room humidity as low as practical, avoid any potential for
condensation. If necessary, heat the room above normal levels and monitor
the humidity. I'd say that below 70% RH max and shoot for 40-60%, but low
won't affect you, other than raising the possibility of ESD.

If you have difficulty with the above, get some office type cabinets with
doors, and install incandescent light fixtures which will be left burning
at all times. Seal the doors with weather stripping to make them relatively
air tight. Place some indicating Drierite in open trays in the bottom of
the cabinets. Check every week or two, and re-activate the dessicant by
baking 6 hrs at 120 degrees C or until the Drierite turns blue, then put it
back in the trays in the cabinets.

Make sure you don't have any sulfur bearing paper in near or direct contact
with the parts. Kraft paper (normal courrugated) is a no-no, so trash any
corrugated bin boxes you may be using. Put the parts in plastic bins or
keep them in the tubes they were shipped in.

I've seen new parts go bad in a few months time when stored in cardboard
boxes. It murders tin-lead plating on copper, I can assure you. Did you
keep those other parts in tape sealed cardboard shipping boxes? The sulfur
concentration in a closed box is much higher...

Store your PWB's in poly bags, and again, avoid cardboard like the plague.

>Leo Reynolds
>Electronic Systems, Inc.
>P.O. Box 5013
>Sioux Falls, SD  57117
>
>Ph 605-338-6868
>Fax 605-338-5061

good luck, and apologies for any obvious pointers you already knew...

Jerry Cupples
Interphase Corp
Dallas, TX