Hi Bev - there have been a number of reported cases of whiskers growing out
of polished microsection surfaces. That highly polished mirror surface is a
great place for some of the metals (aka tin) to change a high energy grain
boundary to a low energy grain boundary.

Dave Hillman
Collins Aerospace
[log in to unmask]

On Mon, Jan 6, 2020 at 2:08 PM Bev Christian <[log in to unmask]>
wrote:

> TechNetters,
> Here are a few provisos though.
> 1) Chemistry still happens, so grain and intermetallic growth will still
> happen although slowly since your samples are presumably stored under room
> temperature conditions.
> 2) Surface oxidation will occur but for tin based solder this is not an
> issue. Could be an issue if you are talking about iron based samples and
> your storage conditions are on the moist side.
> 3) I have seen the growth of lead whiskers out from the surface of
> cross-sections of samples with high lead solders.  I believe this was the
> result of both the pressure and temperature of the curing epoxy, so not
> likely to occur in RT stored x-section samples. However, I have seen enough
> change in the surface of more traditional tin/lead and lead-free samples
> that a re-polish with the finest grit was required.
>
> Regards,
> Bev.
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Stadem, Richard D
> Sent: Monday, January 6, 2020 2:33 PM
> To: [log in to unmask]
> Subject: Re: [TN] storage life of PCB microsection mold
>
> Absolutely!
>
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Bhanu Sood
> Sent: Monday, January 6, 2020 11:10 AM
> To: [log in to unmask]
> Subject: Re: [TN] storage life of PCB microsection mold
>
> And the microsectioned/prepped surfaces are protected from internal and
> external contamination.
>
>
> > On Jan 6, 2020, at 11:44 AM, Stadem, Richard D <[log in to unmask]
> >
> wrote:
> >
> > I would assume it is just about forever as long as it was potted within
> the shelf-live and pot life of the mold potting material.
> >
> >
> > -----Original Message-----
> > From: TechNet <[log in to unmask]> On Behalf Of R Saravanan
> > Sent: Monday, January 6, 2020 10:16 AM
> > To: [log in to unmask]
> > Subject: [TN] storage life of PCB microsection mold
> >
> > Dear all,
> >
> > What is the storage life of the pcb microsection mold . How long we can
> preserve.
> >
> > I am using long curing resin.
> >
> > R.Saravanan
>