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February 2011

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Subject:
From:
Bob Landman <[log in to unmask]>
Reply To:
Bob Landman <[log in to unmask]>
Date:
Thu, 3 Feb 2011 15:01:10 -0500
Content-Type:
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text/plain (174 lines)
This paper shows how Foresite measures contamination on PC boards.
http://www.residues.com/pdfs/Process_control_of_cleanliness_issues.pdf

On page 4 is stated:

Each sample must be extracted prior to having the ion chromatography analysis conducted. We have two extraction protocols that area used in this evaluation. The first is a total board extraction (standard extraction) of the break away coupon with the 68 pin LCC component (top left corner of the umpire photo on page 1). The total extraction is done with a solution of IPA and DI water at 75% IPA and 25% DI water. A 10 ml volume of extraction solution is placed into a Kapak bag and the area of
the board is placed in the bag and then suspended in a water bath at 80C for one hour to extract the residues from the assembly. This extraction solution is then injected directly into the Dionex ion chromatography system that has a 100 uL injection loop that will deposit in the different columns.

Note the use of DI water.... 

Bob Landman
H&L Instruments, LLC


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Forrester, Michael (H USA)
Sent: Tuesday, February 01, 2011 8:57 PM
To: [log in to unmask]
Subject: Re: [TN] PCBA Water Wash

Doug,
 
       We sent defective parts back to the IC manufacturer.  During their failure analysis of the parts (involved opening the
part) they showed clear pictures of gold dendrites between two adjecent pads as well as thinning of the gold bond wires near the area described as migration of the gold to "fuel" the dentrite growth. A surface analysis in the area of the wire bond to external pin showed Chlorine residue.  The dendrite growth was confirmed on other samples sent to a 3rd party lab.  The growth causes intermittent and failed parts.  They are CMOS optocouplers that fail within 10 - 20 days under power.
 
    I will try and contact Mike Bixenman.  Thank you for the contact.
 
Best Regards,
 
Michael Forrester
Sr. Product Engineer
________________________________

From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, February 01, 2011 12:41 PM
To: TechNet E-Mail Forum; Forrester, Michael (H USA)
Subject: Re: [TN] PCBA Water Wash



Michael, 
I will give it a shot. 

1)  Documented, as in a standard "thou shalt use DI water"?  Not really,
no.  It would be considered as a Best Manufacturing Practice though.
Most standards and specifications are based on the theory of we don't
care how you clean it, it just has to meet "X".   

2)  Chloride on electronics is as common as nitrogen in air.  The issue
is how much is present and how free is the chloride to react and do its
dirty work.  What method did you use to determine chlorine
contamination?  I know it takes quite a bit to make gold electromigrate.
In your case, ROSE is worthless, worthless I tell you.  You need to have
your bare boards analyzed by ion chromatography in their incoming state,
and your assemblies tested by ion chromatography after your city water
cleaning process.  That will tell you where your chlorides are coming
from and who to go after when you arm the villagers with torches and
pitchforks.  You can do the same thing on components in the incoming
state to see how much they contribute to the picture. 

3)  Is 80-100 psi too strong?  Depends.  Do you want components on the
board when you are done?  I would suggest a lower pressure, but a higher
volume.  Mike Bixenman of Kyzen Corporation gave an excellent paper on
this at the IPC Cleaning and Coating Conference in December. 

Doug Pauls 



"Forrester, Michael (H USA)" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]> 

02/01/2011 11:08 AM 
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Forrester, Michael (H USA)" <[log in to unmask]>


To
[log in to unmask] 
cc
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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