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
> > > >
> > > > ##############################################################
> > > > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> > > > ##############################################################
> > > > To subscribe/unsubscribe, send a message to [log in to unmask] with
> > > following text in
> > > > the body:
> > > > To subscribe: SUBSCRIBE TECHNET <your full name>
> > > > To unsubscribe: SIGNOFF TECHNET
> > > > ##############################################################
> > > > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > > additional
> > > > information.
> > > > If you need assistance - contact Keach Sasamori at [log in to unmask] or
> > > > 847-509-9700 ext.5315
> > > > ##############################################################
> > >
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> the body:
> To subscribe: SUBSCRIBE TECHNET <your full name>
> To unsubscribe: SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################
|
