Not very likely. The IMC's are Nickel Tins which do not grow very fast at
soldering temperatures let alone at room temperature.
> -----Original Message-----
> From: <Peter George Duncan> [SMTP:[log in to unmask]]
> Sent: Wednesday, November 28, 2001 4:48 PM
> To: [log in to unmask]
> Subject: Re: [TN] BGA long term storage?
>
> How about our afvourite IMC's building up within the component -
> ball/component interface for example? Will that affect long term
> reliability/solderabity after a long period of storage?
>
> Just thought I'ld throw that one into the pot.
>
> Peter Duncan
>
>
>
> "d. terstegge"
> <[log in to unmask] To:
> [log in to unmask]
> GROUP.COM> cc: (bcc: DUNCAN
> Peter/Asst Prin Engr/ST
> Sent by: TechNet Aero/ST Group)
> <[log in to unmask]> Subject: Re: [TN]
> BGA long term storage?
>
>
> 11/28/01 07:08 PM
> Please respond to
> "TechNet E-Mail Forum."
>
>
>
>
>
>
> Hmmm, seems I'm the only one who adviced not to worry about long term
> storage of BGA's. I must admit that I never stored a BGA for 10 years to
> see how it solders, but I really don't expect the solderability to
> decrease
> to such an extend that the balls will not solder anymore.
> According to Klein Wassink the oxidation layer on solder will grow
> approximately logarithmically with time, resulting in about 6nm after 20
> years which is just twice as thick as after one year !
> So my question is: are nitrogen cabinets, ROSA-technology or redesigns
> REALLY necesarry ?
> Maybe one of the metallurgists on this forum can add a few words ?
>
> Daan Terstegge
> SMT Centre
> Thales Communications
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
> >>> Graham Collins <[log in to unmask]> 11/27 1:02 pm >>>
> 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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