Hi David and other metallurgical gurus out there,

If I am trying to decrease the time at which a joint is in reflow to
decrease the wetting onto the connecting trace and maintain solder joint
volumes constant, what are the implications in the solder joint in terms
of intermettalic formation when using Immersion Au?  I am confined to
using the current flux chemistry so my only variable now is decreasing
pre-heat temperature and time and affecting the time of reflow? Am I
missing anything else??

Thanks for any input that you may offer...

Marcelo

> -----Original Message-----
> From: David D Hillman [SMTP:[log in to unmask]]
> Sent: Monday, January 19, 1998 9:54 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Overheated solder joints
>
> Hi Tom - "grainy" solder joints can be caused by three sources: excess
> soldering heat, printed wiring board features and gold finishes. The
> excess
> soldering heat results in the lead phase growth that causes surface
> relief
> that looks 'grainy'. Some printed wiring board internal design
> features
> result in thermal sinks which results in grainy solder joints due to
> slow
> solidification. Soldering to gold finishes can result in the formation
> of
> gold-tin intermetallic phases in the solder joints which cause surface
> relief also. I would suspect that you have grainy solder joints due to
> the
> excess soldering heat phenomena. Unfortunately the assembly you are
> trying
> to solder is a tough one thus the reason for the temperatures you are
> using. You might investigate turning the temperatures down and/or
> looking
> at the board design to see if you can get some improvement. Good Luck.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> [log in to unmask] on 01/16/98 03:20:30 PM
>
> Please respond to [log in to unmask]
>
> To:   [log in to unmask]
> cc:    (bcc: David D Hillman/CedarRapids/Collins/Rockwell)
> Subject:  Re: [TN] Overheated solder joints
>
>
>
>
> I've been asked to give some more information on this defect and how
> it
> occurred.
> First the defect: The solder joints of the effected areas are grainy
> and
> crystalline. Distribution is numerous and random, on the solder side
> only. On the component side flow through is great( this is a
> multi-layer
> board with a large ground plane and weird thermal relief that we have
> struggle in the past to get decent flow thru). Vias and PTHs without
> components are effected as well.
> The description of this as an "overheated solder joint" comes not only
> frrom my DOD-2000 training (defect code A117) but also the conditions
> which produced the "defect."
> The conditions: We are using a Novastar 16FD wave solder machine that
> is
> under two years old (we bought it about 3 months ago). We use an RMA
> flux and clean the boards by hand with "Reliasol". Preheaters were set
> at 430 C (unchanged from previous run of same PWA), but the wave
> temperature was raised 250 C to 260 C to address the bridging.
> Thanks again for your help.
> Tom Moore
> Tom Moore wrote:
> >
> > Technetters,
> > In an attempt to reduce solder bridging between P-T-H leads one of
> > our employees raised the temperature on the solder pot of our wave
> > solder
> > machine. While this did alleviate most of the bridging effecting the
> > boards,on one board type, a multi-layer board, we ended up with
> numerous
> > overheated joints. Unfortunately it effected 27 boards, which for
> our
> > small shop would be a large amount of rework.
> >
> > Reviewing both A-610 and J-STD-001 we didn't see anything that
> called
> > this out as a defect to rework or even a process indicator. Is this
> > correct?
> > Thanks for your help.
> > Tom Moore
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