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Subject:	Re: BGA long term storage?
From:	Graham Collins <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Tue, 27 Nov 2001 07:02:57 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (74 lines)

Hi Doug!
Indeed - not a new problem - and one we have faced on other programs. It's just the BGAs that are new to us for this problem.

Nitrogen storage is available here and I expect that's what we will use (unless some other TechNet guru has a better idea!).

I've heard of ROSA, and in fact Dave was kind enough to send me a 35mm thick document describing some experiments and results with it. Very interesting machine. Do you know if anything ever come of the work to produce a commercial (non-lab) version of this? Hmm... wonder what happened to Bev's?

Anyway - thanks to everyone for the responses. Nitrogen storage was/is the plan, but it is always good to have a sanity check with some experts.

regards

Graham Collins
Process Engineer,
Northrop Grumman
Atlantic Facility of Litton Systems Canada
(902) 873-2000 ext 6215

>>> [log in to unmask] 11/26/01 04:11PM >>>
The issue of long term storage of parts or boards is not a new one. The
military, faced with REALLY long lifetimes (e.g. 50 years for a MX missile)
and decreaseing market clout, has had to deal with lifetime buys for a long
time. In my mind, there are two possibilities: (1) preserve the original
solderability for as long as possible, or (2) plan on restoring the
solderability at some point in the future when the part is needed.

In the first case, you will have to setup some fairly elaborate storage
conditions where oxygen and moisture are excluded. Dry nitrogen is most
common, but alternatives could include dessicated conditions or coverage
with a heavy noble gas like argon. You will have to setup incoming and
outgoing logs that tightly control the inventory, and you have to have
floor space for the storage for the life span of the part.

In the second case, you restore the solderable surface. Some people do
this using aggressive fluxes and re-tinning, with limited success. An
alternative to this is to use an electrochemical reduction process called
ROSA to change the surface oxides to the base metal, restoring
solderability. ROSA can be done on many parts at the same time, it is
electroless, and is not too capital intensive. Dave Hillman of Rockwell is
the master of ROSA and has published a number of papers on the topic. He
would probably answer more fully but he is currently putting the finishing
touches on his Master's thesis and so won't stick his head out of his
cubicle for another few days. And when he does, if he sees his shadow,
there will be 5 more months of winter (in Iowa, that's a safe bet). Where
was I?

The advantage of the ROSA approach is that it does not matter all that much
what the solderability condition was when the part was received, and the
storage conditions do not have to be draconian.

As the commercial goes, you can pay me now or pay me later.....

Doug Pauls
Rockwell Collins

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