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March 2004

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Subject:
From:
David Tremmel <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 3 Mar 2004 14:30:22 -0600
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Hello,

Regarding your first example, chances are you have you have residual flux on
the boards although it depends on who, when and where they were
manufactured.
I have been doing repair of various types of PCBs for years and am confident
without seeing your examples that the residual flux between the leads of
your SMTs in nothing to worry about.

Your example of where the hand soldering was done is definitely an example
of flux residue.  When the heat of a soldering tool is applied to the flux,
the liquids evaporate and the heavier solids remain on the board and become
crystallized or become a very thick and tacky substance.

I am sure that the engineers in the TechNet forum could give you a more
technical answer, but I hope this helps in the meantime.

Have a nice day,

David

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bissonnette,
Jean-Francois
Sent: Wednesday, March 03, 2004 2:19 PM
To: [log in to unmask]
Subject: [TN] Flux Identification and Soldering over gold plated pads???

Got two questions here

First I would like to know if there is a way to identify flux residues on a
soldered assembly.  For instance, I have a series of
board that have a glass like residues between the lead (SMT) and quite a lot
of it.  It looks clear, little bit brownish and it
breaks like glass if I apply pressure with a dentist pick.  Also where hand
soldering was done, the brown color is much 
more obvious.

Second.  Any of you ever seen a board with gold plated lands  instead of tin
plated?  Well I would not be able to say it
it IS gold plated but it sure looks like it and not copper.  

Any help would be appreciated.

Jean-François Bissonnette
Vérificateur, Contrôle de la Qualité
Électronique
Produits et Procédés
Vapor Rail Inc.
10655 Henri-Bourassa O.
St-Laurent, Qc
H4S 1A1

(514) 335-4200 x2021
(514) 335-4231 fax



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