Michael,
You need to contact Terry Munson at Foresite (www.residues.com) and have him do an analysis of your boards.
You need sophisticated contaminant testing; that's what Terry specializes in. Go look at his website - you'll see what I mean. He's developed instrumentation (like his C3 steam extraction instrument which collects samples that are then injected onto a liquid chromatography column to measure the chlorine level.
City water is full of chemicals designed to keep the water safe to drink. It's eating holes in the copper pipes in the Washington DC area [ http://www.wsscwater.com/home/jsp/content/pinholescroll.faces ] and here in New Hampshire and I'm sure elsewhere.
I finally switched to a well at my home after having to pay plumbers to dig up my lawn many times to splice the feeder pipe (holes clearly etched from the INSIDE of the pipe surrounded with GREEN deposits - copper chloride is what I suspect it is.)
[One of my other hats is that I'm a water commissioner for my town]
Good luck! Be sure to let us know what you discover.
Bob Landman
H&L Instruments, LLC
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Tuesday, February 01, 2011 12:41 PM
To: [log in to unmask]
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
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/ContentPage.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
