City water is fine if it is removed (air knife) prior to drying. 

Run the number on dissolved solids content and calculate or weigh the amount
of later left on the board. With a simple blow off you will find the
remaining ionic content is very tiny.

Get ionic contamination tests done. City or DI that test results are the
important issue.

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Forrester, Michael (H
USA)
Sent: Tuesday, February 01, 2011 12:08 PM
To: [log in to unmask]
Subject: [TN] PCBA Water Wash

I have three questions I hope someone can help me with:
 
    1) We have a vendor that uses "city water" directly into their SMT PCA
washer.  I believe DI water is industry standard.
    Does anyone know if it is documented anywhere?  Spec?
 
    2) We had an issue where there was Chlorine contamination and gold
dendrites found inside some standard gull-wing 6 pin SMT ICs.
        This issue seems to be batch related.  The chip manufacturer claims
that chlorine is never used in their process.  Should the SMT 
        process expect to handle the possibility that the wash solution may
get into a part? The PCA vendor uses unfiltered "city water", 
        with no cleaner, in the wash process and does a ROSE test on one
board of each lot.  Since the ROSE test passes, the PCA vendor 
        is blaming the part manufacturer for having "leaky" parts, since the
thinking is the wash is getting into the part and trapped.  
    3) One issue I have is the water pressure in the wash is 80-100 psi.
I think this is too strong, and should be half of that?  You want to 
        flood the board with water, not hit the board and bounce off?
 
    Thank you in advance.
 
Best Regards,
 
Michael Forrester
Sr. Product Engineer
 

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