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February 2011

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Subject:
From:
Robert Kondner <[log in to unmask]>
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Date:
Tue, 1 Feb 2011 19:09:16 -0500
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Paul, 

 Well, try it. Go ahead, tell me the weights of the PCB when dry and then
after wash and blow off. You can easily calculate the equiv ug / in sq.

 And / Or do an ionic contamination test of a DI and that same board you
measured above. I would love to see the numbers. My problem was I did not
have a scale with the required sensitivity.

Instead of anything with an "I have seen ...." do an "I did this experiment
and this is what I measured"  type statement.

Enquiring Minds Want to Know!  :-)

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Tuesday, February 01, 2011 2:02 PM
To: [log in to unmask]
Subject: Re: [TN] PCBA Water Wash

I disagree with Bob...

I have never seen an air knife remove water from all the spaces that can be
on a board...

The work fine if you have plenty of clearance between ALL surfaces... 

I have seen air knives drive water into spaces where to water's natural
surface tension would NOT allow it to go...

When the water evaporates, if it evaporates, it leaves the organo-halogen
complexes that supply base materials for dendritic growth...

Paul

Paul Edwards
Process/Quality Engineering
Surface Art Engineering


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Tuesday, February 01, 2011 10:23 AM
To: [log in to unmask]
Subject: Re: [TN] PCBA Water Wash

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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