Jean-Francois,

Are these boards HASL or some other surface finish? I am going to assume for
the moment that the boards are HASL since you mention fluxes.  In this case
the answer to your question is yes, contamination can come from the HASL
fluxes. I have seen this numerous times in the testing that I have done over
the years.
Many times fabricators will use HASL fluxes that are either chlorinated or
brominated materials and if not properly removed can leave behind
potentially harmful residues.  What specific Halogen substance did the test
lab indicate or did they? Did they use the term Halogen or Halide? Can you
be a bit more specific about the failure? Also, what is your manufacturing
environment?  (Water-soluble, no clean, etc.)

The amount of allowable incoming contamination from fabricators will depend
to some extent on the type of processing environment. If you are a no clean
manufacturer, then the fabricator should be providing you the cleanest
possible boards they can.  Because the higher the residues from the
fabricator plus the residues from the manufacturing equates to higher
residues on the final assembly.  Whether or not a no clean assembly will be
at risk for electrochemical failures (dendritic growth or corrosion) will
depend on the amount of the different residue types either individually or
collectively.

In a water-soluble type of environment the amount of allowable incoming
contaminates can increase a bit since cleaning will be done at the end of
the process.  I would like to point out though that as fab residues are
exposed to reflow conditions they become harder to remove. The more times
through reflow the harder they are to clean.  So a good rule of thumb is to
have the cleanest incoming bare boards possible regardless of process type.

If your boards are a cold plated process such as immersion silver, tin, or
ENIG, then there are other residue sources.  This is where it would be nice
to know what specific contamination was found and the actual surface finish.

So I will digress and let some of the other Tech guru's comment.  If I can
be of further assistance to you feel free to contact me.

Best Regards,

Joe Russeau
Process Analyst

Precision Analytical Laboratory, Inc.
4106 Cartwright Dr. Ste. A
Kokomo, IN 46902

P: 765-455-1993
F: 765-455-1996
E: [log in to unmask]


----- Original Message -----
From: "Bissonnette, Jean-Francois" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, May 13, 2005 7:20 AM
Subject: [TN] Halogen Contamination


> Hi all,
>
> We recently had a number a failures on MOSFETs and set samples for
> analysis.  The analysis from the supplier said that some chemical
> contamination occured and it's related to an halogen subtance.
>
> Can anyone tell me in a board fabrication process where such a
> contamination occur?  Are fluxes containing halogen substances, cleaning
> products etc.
>
> Thanks in advance!
>
> J-F
>
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>

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