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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 6 Jun 2000 09:34:52 +0300
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Hans

Offhand, no. I would suggest you contact the laminate manufacturer. However, I do know that
there have been papers published on the subject, mainly from academic sources totally
unrelated to electronics laminates. I think that the now defunct polymers laboratory in the
Materials faculty of the Swiss Federal Institute of Technology, Lausanne (EPFL) had a
student who did his dissertation on this subject about 15 years ago, under Prof. Kausch,
but I'm not even sure of this. Otherwise, one of the large epoxy makers may have data. I
don't know the mechanism, but it may have something to do with the residual ionics from the
prepolymerisation reaction.

Brian

Hans Rohr wrote:

> Brian,
>
> Do you know of any published data that shows a relationship between the decrease in Tg
> with increasing board moisture content?  I am doing a failure analysis on a one year
> old board that has a measured Tg (by DSC) that is 12 degrees C lower than when it was
> fabricated.  The moisture content of the board is close to 8,000 ppm.  The DSC scan did
> not exhibit a double peak.  A very small quantity of boards exhibited massive
> delamination after SMD reflow.  The remainder of the boards from the fabrication lot
> were run several times over a 2 month period and exhibited no sign of delamination.
>
> Hans Rohr
>
> Brian Ellis wrote:
>
> > Tim
> >
> > The thermal energy required to remove ab/adsorbed water molecules from a
> > heterogeneous material is about the same, irrespective of the temperature
> > (within reasonable limits and provided you do not have a phase change, such as
> > exceeding the Tg, which, incidentally, drops by about 20 °C when the board is
> > humid). If you use a vacuum oven, you have extra energy required to turn the
> > pump and operate the traps. The pump runs hot, after a time, and this heat is
> > dissipated into the atmosphere and not into the oven. If you use a cryogenic
> > trap to prevent oil vapour from entering the oven or moisture from emulsifying
> > the lubricating oil, this also requires energy to produce the removal of heat.
> > If you use absorber/adsorber traps, they require energy to regenerate. Overall,
> > vacuum drying requires 50-100% more energy than atmospheric pressure drying,
> > albeit the temperature may be considerably lower.
> >
> > Brian
> >
> > Timothy Reeves wrote:
> >
> > > When you say that the energy is actually greater, you mean the energy
> > > imparted to the escaping water molecules, right? But what does that matter?
> > > What really matters is energy imparted to the board. The board itself may
> > > actually decrease in temperature if a low enough pressure is obtained. In
> > > that sense, Doug was right (but he should have said "less heat [transferred
> > > to the polymer, glass, and copper]")
> > > I know... you were just trying to point out the misconception most people
> > > have regarding temperature vs. heat.
> > > I love these technical arguments... :-)
> > > Tim Reeves
> > >
> > > > ----------
> > > > From:         Brian Ellis
> > > > Sent:         Thursday, June 1, 2000 7:54
> > > > Subject:      Re: Baking of boards
> > > >
> > > > Sorry, Doug, the heat is more or less the same. The energy required is
> > > > actually
> > > > greater. It is the temperature that is lower.
> > > >
> > > > Brian
> > > >
> > > > Douglas Pauls wrote:
> > > >
> > > > > If you are really concerned about the effects of heat on the polymer
> > > > > qualities or the oxidation of the surfaces, consider using a vacuum or
> > > > > vacuum-make operation.  Gets the water out with less heat.
> > > > >
> > > > > Doug Pauls
> > > > >
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