> >
> > > -----Original Message-----
> > > From: moonman [SMTP:[log in to unmask]]
> > > Sent: Tuesday, January 13, 2004 2:29 PM
> > > To: Dehoyos, Ramon
> > > Subject: Re: [TN] reflowing 0402 SMT capacitors with underside
> > termination s
> > >
> > > Hey Ramon,
> > >
> > > How you doing?
> > >
> > > The phased reflow profiles can do a lot for this condition. You simply
> > > determine the ones that will work with your solder pastes and your
other
> > > soldering requirements.
> > >
> > > I never have liked to use an non-eutectic solder of any type but in
> these
> > > cases, as Steve said, a 2% silver formulation can be beneficial for
the
> > same
> > > basic reasons as phased reflow. Simply, the small chip devices have a
> > > buoyancy that prevents proper wetting so they "float" in all
directions
> > > starting with up as there are no end terminations to be "grabbed" and
> > held,
> > > via wetting, during the soldering process.
> > >
> > > Using phases or "phased" solder pastes provides time for the devices
to
> > > "adhere" to the solder without "roaming" all over. The Ag2 goes
through
> > > phases pure eutectic pastes do not. They go through a minor plastic
> phase
> > > whereas eutectics go from solid to liquid without the plastic phase.
> > >
> > > I have had problems coming up with "good," well balanced profiles,
using
> > > phased reflow soldering, that satisfy my requirements for what I would
> > call
> > > good wetting for all components of varying thermal densities or of
> varying
> > > solder termination differences. Something personal I guess or maybe I
> just
> > > didn't take enough time. As a team we managed to get the job done but
it
> > was
> > > a trial.
> > >
> > > Another thing to be considered is the solder paste volume that needs
to
> > > minimal but enough to effect acceptable solder joints. However, with
> these
> > > things - what is acceptable? The question must be asked for obvious
> > reasons.
> > > The other major point to be considered is the solder termination
> geometry
> > > and size. Again, I and many others use minimal pad sizes for most chip
> > > devices with very small solder joints. Another consideration would be
> > using
> > > the "home plate" design for many small chip devices though I've not
yet
> > > tried them for the devices in question.
> > >
> > > Lots' to be considered not the least of which, again, is what is an
> > > acceptable solder joint and how do you determine it. I've read little
> > about
> > > initial quality or long term reliability investigations. Have you?
> > >
> > > Personally, I think these little devices should be outlawed
> > >
> > > Keep me posted and take care,
> > >
> > > MoonMan
> > >
> > > ----- Original Message -----
> > > From: "Dehoyos, Ramon" <[log in to unmask]>
> > > To: "moonman" <[log in to unmask]>
> > > Sent: Tuesday, January 13, 2004 11:27 AM
> > > Subject: FW: [TN] reflowing 0402 SMT capacitors with underside
> termination
> > s
> > >
> > >
> > > >
> > > > > Some of the big guns are away and have not
> > been
> > > > > heard from.What do you think about this 0402 chip problem Moonman?
> > > > > Regards,
> > > > > Ramon
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Steve Gregory [SMTP:[log in to unmask]]
> > > > > > Sent: Monday, January 12, 2004 3:23 PM
> > > > > > To: [log in to unmask]
> > > > > > Subject: Re: [TN] reflowing 0402 SMT capacitors with
> underside
> > > > > terminations
> > > > > >
> > > > > > Hi Tom!
> > > > > >
> > > > > > There's a few articles out there that talk about "Phased Reflow
> > > > > Soldering".
> > > > > > Here's a link to one:
> > > > > >
> > > > > >
> > >
http://www.reed-electronics.com/semiconductor/index.asp?layout=article&
> > > > > > articleid=CA274087&industryid=3026
> > > > > >
> > > > > > Something I've done in the past that works really well in my
> > opinion,
> > > is
> > > > > to>
> > > > > > use a 2%
> > > > > > silver solder paste. Sn62/Pb36/Ag2...works in the same way that
> > Phased
> > > > > Reflow
> > > > > > does.
> > > > > > The difference is pretty dramatic when it comes to eliminating
> > > > tombstones!
> > > > > >
> > > > > > -Steve Gregory-
> > > > > >
> > > > > >
> > > > > > > Greetings All,
> > > > > > >
> > > > > > > I am having my first experience working with an assembly
design
> > that>
> > > > > > > involves 0402 capacitors with underside solderable
terminations
> > > (vice
> > > > > > > wrap-around end terminations)... The reflow process seems to
> cause
> > > the
> > > > > > > components to tilt and skew to highly unacceptable levels.
> > > Physically
> > > > it
> > > > > > > looks as if the caps floated to the top of the molten solder
> > volume
> > > > (as
> > > > > if
> > > > > > > on pontoons) then slid down one way or the other. The vendor
> made
> > a
> > > > few
> > > > > > > recommendations including migration to a thinner (4 mil)
stencil
> > as
> > > > well
> > > > > as
> > > > > > > some pad design and nitrogen tweaks and... Even after
> implementing
> > > > these
> > > > > > > recommendations we are experiencing the same problems, just to
a
> > > > > slightly
> > > > > > > lesser (although still unacceptable) degree... Does anyone out
> > there
> > > > > have
> > > > > > > any additional thoughts on how to remedy this sort of issue?
> > > > > > >
> > > > > > > We do build another part [successfully] with a similar style
> > > > component,
> > > > > but
> > > > > > > it is a 1206 form factor and is perhaps massive enough to keep
> > from
> > > > > floating
> > > > > > > up the way the 0402 caps do...
> > > > > > >
> > > > > > > Your collective wisdom is greatly appreciated!
> > > > > > >
> > > > > > > Best Regards,
> > > > > > >
> > > > > > > Tom Ochenas
> > > > > > > Process Engineering
> > > > > > > Maxtek Components Corporation
> > > > > > > 2905 SW Hocken Avenue
> > > > > > > Beaverton, OR 97005
> > > > > > > [log in to unmask]
> > > > > > > desk: 503-627-3078
> > > > > > > fax: 503-627-4651
> > > > > > >
> > > > > >
> > > > > >
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