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December 2010

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Subject:
From:
Bob Landman <[log in to unmask]>
Reply To:
Bob Landman <[log in to unmask]>
Date:
Fri, 3 Dec 2010 13:17:10 -0500
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John Anselmo,

Tape the vents with Kapton film or liquid mask then do the water-washable assembly, clean the boards then remove the tape/soldermask.

The vents are there for a long term problem (venting material from the soldermask under the lid or the chemicals in the FR4 in the small pc board that is under the lid. The board is there for the bypass capacitors.  

A presentation by Xilinx on how they assemble their parts explains the issues.
http://www.hlinstruments.com/Foresite/wp236_Flip%20chip%20package%20design_construction.pdf

You can read (and see pictures) at this link about the problem
http://www.hlinstruments.com/Foresite/

Bob Landman
H&L Instruments, LLC
www.hlinstruments.com
LDF Coatings, LLC
www.ldfcoatings.com


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Friday, December 03, 2010 9:52 AM
To: [log in to unmask]
Subject: Re: [TN] DI Wash of Xilinx BGA

Hi folks! Bill Vuono of Raytheon gave a great ppt at the IPC/SMTA Cleaning & Conformal Coating Conference a couple of weeks ago which would be a beneficial reference material for this issue. Look for the following presentation title "Resolving the Issue of Cleaning Fluid Entrapment Under Vented Flip Chip Packages"


Dave Hillman
Rockwell Collins
[log in to unmask]




John Goulet <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/03/2010 08:40 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask]


To
[log in to unmask]
cc

Subject
Re: [TN] DI Wash of Xilinx BGA






To John Anselmo 

The Xilinx wash spec recommends baking afterwards to assure the part is 
dry. In practice blow out the water with an air gun to assure there is no 
water under BGAs, the heated board will then dry. 

The hot water 140-145F will safely dissolve the OA flux from the other 
components and posses no risk to BGAs. 



However from a processing time, double handling and risk damaging or 
knocking off bottomside SMT chip components in the wash  you may want to 
consider putting on the post wave parts with a No-Clean flux pen. Just 
flux the topside holes prior to inserting the part with the flux pen. If 
the customer doesn't allow any No-clean residue then 3M makes an excellent 
cleaner that the operator can use after hand solder. The product flow 
continues and uses less racks etc. 

If you would like info on a safe cleaning mat designed for cleaning SMT 
boards in an in-line aqueous cleaner that prevents all of the aqueous 
cleaning/board handling related issues just E-mail me.  

John Goulet 

MFG/Process Engineer 

  
----- Original Message ----- 
From: "John Anselmo" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Thursday, December 2, 2010 11:59:53 AM 
Subject: [TN] DI Wash of Xilinx BGA 

Hi all, 

  

I have a processing question.  We are building a CCA with a Xilinx 256 
ball BGA. 

The problem is there will be some components added after the BGA is 
placed. 

Normally we used water soluble flux in hand add. 

Is it okay to wash the CCA's with the BGA already placed? 

  

I found some information in the archives (one email string recommending 
sealing the BGA to prevent water from getting under the lid). 

Any other issues with a DI water wash? 

  

Thanks, 

  

John 

  


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