First off I will preface this by saying that our experiences are limited to rosin based fluxes (e.g. not "water solubles", newer "no cleans".)

First off regarding cause, we find that it is typically caused by a combination of excessive heating during preheat or soldering, the type of flux and the cleaner used.  One particularly useful way of preveing orat least cutting down on amount of residue was to switch (again in the class of rosin fluxes) from a "water white" rosin to a "tall oil" type.  (Contact your flux vendor regarding specific formulations."

In the case of rosin fluxes, we explictly tested if the residue would promote dendritic growth and found that it didn't.  If you contact me directly (via phone) we can discuss specifics.

Jim

========================
Jim Maguire
Associate Technical Fellow
Boeing - Phantom Works
Electrical/Electronics M&P
(253)657-9063
fax   657-8903
[log in to unmask]
========================



> ----------
> From:         Calvas, George (G.)[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Calvas, George (G.)
> Sent:         Monday, February 15, 1999 12:48 PM
> To:   [log in to unmask]
> Subject:      [TN] White Residue between Solder Pads
>
> I read a posting on white residue between solder leads.  I was hoping you
> could give me insight of the probability of dendridic growth based on the
> solder/flux combinations as well as the different cleaning solutions that
> are used.  I have been told that the residue (flux or cleaning solution?)
> with proper humidity, bias and temperature could cause dendridic growth to
> spread across adjacent  leads which would obviously be a detrimental
> failure.  I am using surface mount devices of .050 spacing and .025 lead
> width on an FR4 material.  One final question, Is it the residual flux or
> the cleaning solution or both that causes this anomaly.  I would appreciate
> any insight to this problem.  Thank You.
>
> George Calvas
> Visteon Racing
> Visteon Automotive Systems
> Tel: 734-458-0307
> e-mail:  [log in to unmask]
>
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