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July 2008

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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]>
Date:
Fri, 25 Jul 2008 12:40:19 -0400
Content-Type:
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Or do ionograph test for every asy right after rework
... Just kidding 
--------------------------
Sent using BlackBerry


----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Fri Jul 25 12:12:00 2008
Subject: Re: [TN] Cleaning WS fluxes and other evil

1. with a good water wash, just th same as when you solder the beastie 
with a WS flux. No messing, no short cuts.

2. categorically NO! Alcohol may not dissolve the residues, either 
organic or metallic

3. Yes! This is why you need to give it a full-scale wash. You cannot 
clean with a brush: all you will do is harm by spreading those ionics 
all over the place.

WS=WATER soluble - un point, c'est tout!

Brian

Jean-François Bissonnette wrote:
> Hello Technetters,
> 
>  
> 
> We experienced some problems after reworking circuit boards, I would like to have inputs on the following.
> 
>  
> 
> The problem found is capacitor leakage.  The capacitor was added manually after automated production.  The boards were coated with acrylic conformal coating.
> 
>  
> 
> 1-       How should a WS flux be cleaned after a rework?
> 
> 2-       Can WS be cleaned with alcohol?  If not what would happen?
> 
> 3-       When reworking a SMT component, can WS flux be trapped under the component and cause leakage.  The rework was cleaned with a brush or similar method.
> 
>  
> 
> We think that the rework method was as follow (to fix a possible contamination under the component)
> 
> a-       SMT component is removed (possibly directly through the conformal coating)
> 
> b-       Using coating thinner, the area is cleaned and verified under UV to ensure no coating is present.
> 
> c-       WS flux is added
> 
> d-       Component is soldered back in place
> 
> e-       Area is cleaned with isopropyl alcohol
> 
> f-         Coating is added
> 
>  
> 
> I think I've read that cleaning WS flux with alcohol is a NO NO!  Can anyone confirm and comment? 
> 
>  
> 
> Jean-Francois 
> 
>  
> 
> 
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