Hector -
Thank you for reminding me. I completely agree with you. Unlike some other
processes, if you only have one or a few boards to reflow, at least you
don't have to worry about burning up the board or components if you have the
wrong profile. Additionally, it had been reported in the literature several
years ago, of the much lower incidence of the "popcorn" effect due to
moisture absorption on larger plastic devices if you kept the temperature
below a critical temperature. As I recall, that critical component
temperature was around 230 C, but don't quote me. I'd have to search back
through the literature. Anyhow, vapor phase gave you an additional safety
margin for components that were not baked or were improperly baked.
Ed Valentine
Electronics Manufacturing Solutions
8612 Mourning Dove Road, Raleigh, NC 27615
Phone: (919) 270-5145, Fax: (919) 847-9971
Email: [log in to unmask]
Website: http://www.ems-consulting.com
----- Original Message -----
From: Valladares, Hector A (FL51) <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 03, 2000 4:50 PM
Subject: Re: [TN] vapor phase reflow
> Hi Ed,
> We have been using vapor phase reflow since 1992. The one advantage that
no
> one has seem to mention is that you can get 100% reflow on all components
> from the first PWA you assemble. We make some very expensive Single Board
> Computers PWA for space applications that the PWA alone can cost over $4K
> and has 24 layers. In a substantial amount of cases your are only building
5
> or 10 of a certain type. If it has to work 100% of the time from the first
> PWA you profile, vapor phase is it. If you can afford to get a good sample
> of completely populated PWA then forced convection will work out better. I
> agree the fluid is expensive but once you set the profile you don't have
to
> worry about a part change effecting your process. I think Dupont K-6 fluid
> boils at 221C.
>
> Hector Valladares
> Honeywell -SASSO
> Production Staff Engineer
> 727.539.3683 voice
>
>
>
>
> -----Original Message-----
> From: McMonagle, Mike [mailto:[log in to unmask]]
> Sent: Friday, March 03, 2000 2:45 PM
> To: [log in to unmask]
> Subject: Re: [TN] vapor phase reflow
>
>
> Ed,
> Thanks for the due respect, I'll take it wherever I can get it. I
do
> not disagree with the points that you, Brian or Larry have raised, vapor
> phase can have great benefits in certain instances. However, it is not a
> process to move into without a good reason for doing so. And in the
majority
> of applications, a modern forced convection reflow system will achieve
> desired results without the high costs that can be involved with vapor
> phase. Brian's points regarding the GWP of these materials is another
> negative looking towards future usage, it is just a matter of time before
> they become heavily regulated, taxed and ultimately outlawed ala CFCs and
> lead. Even 3M makes note of the high GWP of Fluorinert in their data
sheets,
> right after they trumpet the fact that they are VOC free. Finally, the
> current selection of perfluorinated fluids will not exceed a temperature
of
> 215C, ruling out use for high-temp alloy soldering. The FC-71 you
mentioned
> was discontinued by 3M without replacement back in 1989-1990 due to lack
of
> demand, and there is no other manufacturer I'm aware of making anything
with
> a boil point above 215C.
>
> Mike McMonagle
> PCBA Process Engineering
> Telxon Corporation
> (713) 307-2443
> www.telxon.com
>
> -----Original Message-----
> From: Edward J. Valentine [mailto:[log in to unmask]]
> Sent: Wednesday, March 01, 2000 2:34 PM
> To: [log in to unmask]
> Subject: Re: [TN] vapor phase reflow
>
>
> Jason -
>
> With all due respect to Mr. McMonagle, vapor phase reflow with preheating
> (an integral part of many units since the mid-80's), can produce excellent
> results in very dense assemblies and backplanes. The chief advantage is
its
> very even heat distribution over the assemble. The highest temperature
> fluorinated liquid that I am familiar with is FC-71, which has a higher
> boiling temperature than the 215C (419F), FC-70. The FC-71 is 250C
(495F).
> The liquids are very expensive, but the only fluids that were/are
regulated
> were the secondary fluids (Freons), not the Primary fluorinated fluids
since
> they are not a HFC or cause any effect on the ozone, nor are they a
> regulated contaminant,but that may vary at some locales. Generally,
forced
> convection is the preferred reflow process, but it is not a panacea for
all
> applications.
>
> If you would like to discuss some more, please feel free to contact me
> offline.
>
> Ed Valentine
> Electronics Manufacturing Solutions
> 8612 Mourning Dove Road, Raleigh, NC 27615
> Phone: (919) 270-5145, Fax: (919) 847-9971
> Email: [log in to unmask]
> Website: http://www.ems-consulting.com
>
> ----- Original Message -----
> From: Jason Gregory <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, March 01, 2000 8:53 AM
> Subject: [TN] vapor phase reflow
>
>
> > Hello techies!
> >
> > I am looking for anyone who has performed any qualifications on the
> advantages/disadvantages of vapor phase reflow. Particularly dealing with
> higher temp alloys. Is it the way to go? Is convection better? Who are the
> major manufacturers? Are silicon castments to keep the bottomside
components
> from falling off mandatory? Any replies are GREATLY appreciated.
> >
> > Jason Gregory
> > Production Manager
> > Electrospec
> > (713)784-4900
> > (713)784-1194 fax
> >
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