I've heard the reason is that high purity water is a rather unstable
substance and as such is "ion hungry". 

Recall a story (urban "technet" legend?) which recounted how years ago
Wang (?) had a custom SS cleaning system that used ultra pure DI. Over
time the welded seams were eaten away and the system dumped on the
floor.  

Rich K / Kimball
847-621-7310
 
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Friday, March 07, 2008 4:27 AM
To: [log in to unmask]
Subject: Re: [TN] Effects of rinsing with high purity water.

I'll offer you a guess, without any scientific knowledge to back it up. 
If the Au is porous, the Ni could be attacked with OA residues diluted 
during the first wash, leaving nickel halides in the pores. The high 
surface tension of the final rinse water may prevent them from being 
removed but the Au/Ni couple with the damp residues could make a nice 
corrosion cell. Plausible?

Brian

Peter Barton wrote:
> Hello Technetters,
> 
> There has been some comment on this forum recently implying that
cleaning or 
> final rinsing of assemblies with high purity DI water can have a
detrimental 
> effect on solderability. We very occasionally see a solderability
issue when 
> processing second side surface mount after first side population and 
> cleaning. Because of product build times and the use of paste with an
OA 
> flux that must be cleaned soon after soldering we have to wash the
first 
> side before continuing with the second side.
> 
> The surface finish of the PCB concerned is ENIG. We have had various 
> analyses carried out on the surface finish but have never had any
conclusive 
> evidence that the finish itself contributes to the problems seen.
> 
> Can one of the gurus please explain how high purity water could affect

> solderability and, if there are any circumstances in which variation
in ENIG 
> could be susceptible to degradation in solderability if cleaned this
way.
> 
> Best rgds,
> 
> 
> 
> 
> 
> 
>
-----------------------------------------------------------------------
> Peter Barton
> Senior Process Engineer
> ACW Technology Ltd
> Dinas Isaf West
> Tonypandy
> Mid Glamorgan. CF40 1XX  Wales
> 
> Tel: 01443 425275 (direct)
> Fax:  023 8048 4882
> International Tel : +44 1443 425200
> International Fax : +44 23 8048 4882
> Website/URL:  www.acw.co.uk
> 
> ---------------------------------------------------
> 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.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
> -----------------------------------------------------
> 

---------------------------------------------------
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.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
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.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------