Hi Dave
You know that strictly speaking ANY KINETIC PROCESS WILL ALMOST NEVER STOPS but yes it can slow down significantly depending on the activation energy.
The same goes to intermetallics at the UBM side but I totally agree it would be of no concern.
Regards,
Vladimir
Sent from my BlackBerry 10 smartphone on the Rogers network.
Original Message
From: David Hillman
Sent: Tuesday, April 7, 2015 15:10
To: [log in to unmask]
Reply To: TechNet E-Mail Forum
Subject: Re: [TN] 5 year old BGAs
Hi gang - hate to destroy an industry myth but tin oxidation is pretty much
self limiting. The oxidation reaction will hit a plateau around 40 nm and
then stop. Most long term solderability loss isn't from oxidation of the
external interface but rather the consumption of a tin layer from
intermetallic growth over time. Since a BGA typically has a SMD gold over
nickel over copper pad (the gold is consumed during ball attach) and the
IMC growth of tin/nickel is very slow, once the solderball outer surface
hits the 40 nm mark, solderability isn't going to change, especially if
MSL/inert gas packaging is used.
Dave
On Tue, Apr 7, 2015 at 1:52 PM, Stadem, Richard D. <[log in to unmask]
> wrote:
> Drypak alone won't do any good unless the it is done with nitrogen. The
> oxidation will continue unless all Oxygen is purged and the hermetic bag is
> sealed.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
> Sent: Tuesday, April 07, 2015 1:42 PM
> To: [log in to unmask]
> Subject: Re: [TN] 5 year old BGAs
>
> low temp storage with hermatic seal package (dry pack)... pack in a way
> according to your forecast usage level (once a year for example or every 6
> month). if it is programmable device, make sure you still has computer and
> program to run for it... check solderability every year. just in case you
> see problems, you have time to final alternative, like re-design-usually
> take 3-6 month go through qual (not if you want to, but
> 5 years anything can happen)...my 1.6 cents.
> jk
> > Hi Peter - Sue and Richard gave you the critical parameter = proper
> > storage. The two primary processes you want to stop or significantly
> > slow
> > down: the oxidation of the solderballs and the absorption of water by
> > the BGA laminate/molding. If you use the industry MSL bags designed to
> > control moisture diffusion, use desiccant, use an inert gas such as
> > argon or nitrogen and then store the bags in a controlled environment,
> > you will address both issues and should be able to get a 5 year use
> > life. Most folks try to cut corners/costs and do things cheaply which
> > dooms their potential for success.
> >
> > Dave Hillman
> > Rockwell Collins
> > [log in to unmask]
> >
> > On Tue, Apr 7, 2015 at 8:53 AM, Peter G. Houwen
> > <[log in to unmask]>
> > wrote:
> >
> >> We have an FPGA that may not be available to us soon. One of the
> >> options available to us to avoid a redesign is to buy 5 years' supply
> >> of the BGA.
> >>
> >> I'm being asked to analyze the risk factors (and we need an answer
> >> today of course)
> >>
> >> We can easily bake parts for moisture, but what about plating
> >> degradation on the balls? Any other problems I might expect?
> >>
> >> I assume that even with baking we should expect some yield reduction,
> >> but I can't begin to guess how much.
> >>
> >> Thanks,
> >>
> >> Pete
> >>
> >
> >
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