Yves:
There are a couple of issues you have touched upon. First glass
transition of the temperature of most plastic packages range from
140C~165C (in certain power devices, there are Tg's which can go as high
as 190~200C). So soldering/reflow temps are well above the Tg.

The fundamental issue with moisture sensitivity is the rate at the
internal pressure builds. When it exceeds the yield strength of the
package or of the wire bond attachment (or in some cases the die attach
adhesive tensile strength limit), we have failures. By most accounts,
there is no magical number. JEDEC regimens have bakeouts at 125C, with
no ramp defined. In the early days of the MSD ad hoc committee (headed
by Ray Prasad at Intel), we had performed bakeouts at 150C.

Try looking at IPC-SM-786A or JESD22-A112 (www.eia.org) for more info on
bakeout regimens, etc.

Regards,
> Bill Davis, Ph.D.
> Diamond Multimedia Systems
> Senior Scientist
> Tel. 408.325.7868
> Cell. 408.888.5650
> e-mail: [log in to unmask]
>
>
>
>
> -----Original Message-----
> From: Yves Trudell [SMTP:[log in to unmask]]
> Sent: Friday, November 13, 1998 12:56 PM
> To:   [log in to unmask]
> Subject:      [TN] Moisture Sensitive Devices
>
> With respect to a saturated moisture sensitive device, what is the
> maximum
> temperature (and ramp) that the device can reach before it becomes
> damaged
> (delaminated)?  Most references just say that you shouldn't put it
> through
> reflow. Our ovens are set to max out at 215 deg C. So, if I brought
> the
> saturated device up to say 200 deg C (which is less than our reflow
> profile)
> then would I damage it?  If I had to guess, I'd guess that we should
> be safe
> as long as we're below the glass transition of the plastic.  But  If
> there
> is a general "magic" temperature for a saturated device, is it only
> important that the plastic over the die stay below this temperature,
> or is
> it the plastic over the die and leadframe (this is important for
> repairs
> using soldering irons or hot air pencils to touch up solder joints).
> I'm not looking for a quote of an acceptable oven profile for smt
> devices
> that are not saturated.  The reason that I'm talking about saturated
> devices
> is with respect to PCBAs that may spend time in a debug queue that
> eventually get hit with a hot air pencil to touch up solder joints.
> We
> don't want to send delaminated devices out the door.
>
> And NO, I don't have a Sonoscan... although I wish I did.
>
> Yves Trudell
> Nortel, Wireless Networks Calgary
> Quality System Engineering
>
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