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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