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July 2008

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Subject:
From:
Jean-François Bissonnette <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Jean-François Bissonnette <[log in to unmask]>
Date:
Fri, 25 Jul 2008 09:58:43 -0400
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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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