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Re: Phase Change Memory

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"Paul Rubin" <no.email@nospam.invalid> wrote in message
news:7x7gukn3cq.fsf@ruckus.brouhaha.com...
> [...] PCM [...]
>
> I do worry about data retention at high temperatures.

Which high temperatures: operating or manufacturing?

Bernd said it's a BGA package...  Heat is especially bad for BGAs - which
will unsolder themselves.  The chip heats up, expands or twists, applies a
stress/strain, excessive heat unsolders a "pin", it moves, disconnects from
circuit...  BGAs becoming unsoldered is the reason your XBOX 360 or
ultra-expensive high-end video card dies.

I'm not sure what the soldering temperatures are for surface mount or BGAs.
I'd assume they're somewhat less, maybe substantially less, than
through-hole since the solder doesn't have to wick into holes.  A wave
soldering machine is what solders through-hole circuits.  For a wave
soldering machine (AIR - this was some 15 to 20 years ago), the air
temperatures were 700 to 800 degrees Fahrenheit (371 to 426 degrees
Celsius), and the molten solder was 450 degF (232 degC).  *Everything* on
the board was hot enough to burn you badly.  Shields were constructed to
prevent plastics from melting.  Those temperatures were high since they
chose to switch to a bio-degradable water-based flux, instead of a solvent
based flux.  I.e., they had to drive off quite a bit of water to leave flux
on the board.  The water had to be removed before entering the "fountain" of
molten solder, or the solder would splatter leaving lead balls all over the
circuit board...

> The blurb says that the heat of soldering a chip to a circuit board erases
> the data.

That seems to indicate the phase change material has a "low" temperature for
it's phase change, at least relative to production soldering temperatures.

> I'd like to think heating the pins doesn't cause the actual chip die to
> get all that hot.

During manufacturing?   They had IC packages where the casings separated
from heat from soldering.  I.e., the top case separated from the bottom case
and exposed the die to air (died upon power-up).  That was most likely due
to the higher temperatures used in that company's process and some cheap
ICs.  More expensive ICs of the same type didn't fail that way.

Or, by hand soldering?  If a hobbyist is soldering the chip, the temperature
of the soldering iron is much lower.  However, they can still overheat it
and cause it to fail.  This happens if they solder too many pins too quickly
causing heat to buildup.  Do one or two.  Let cool.  Repeat.

> So I worry about high ambient temperatures erasing
> the data.

Once it's through manufacturing, if it's still operating and wasn't heat
damaged, it'll be operating at much "lower" temperatures from then onwards.
But, if the PCM temp is too low, or you have old heat sink grease or
insufficient heat sinking, I could see data loss as a real possibility.  If
the PCM memory is enclosed, I could see heat build up as being an issue too.
Repeated heating cycles can cause cracking or stress or strain related
failures too.

Do you remember how hot the first CD-burners made CDs by the time they were
done burning?  Sometimes, you couldn't access them later because they shrunk
so much when cooled.

This PC is the first one, of dozens, where I haven't had to change the
thermal grease for the processor after a few years because of heat failure
of the grease.


Rod Pemberton

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Thread

Phase Change Memory Jason Damisch <jasondamisch@yahoo.com> - 2012-07-02 08:39 -0700
  Re: Phase Change Memory "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-07-02 19:45 -0400
    Re: Phase Change Memory Mark Wills <markrobertwills@yahoo.co.uk> - 2012-07-03 03:29 -0700
      Re: Phase Change Memory Paul Rubin <no.email@nospam.invalid> - 2012-07-03 10:47 -0700
        Re: Phase Change Memory Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-04 00:38 +0200
        Re: Phase Change Memory Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-04 02:06 +0000
          Re: Phase Change Memory Paul Rubin <no.email@nospam.invalid> - 2012-07-04 10:04 -0700
        Re: Phase Change Memory "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-07-04 05:05 -0400
          Re: Phase Change Memory rickman <gnuarm@gmail.com> - 2012-07-04 12:33 -0700
            Re: Phase Change Memory "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-07-04 21:48 -0400
              Re: Phase Change Memory rickman <gnuarm@gmail.com> - 2012-07-05 09:57 -0700

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