Doug,
And if that toast is a multigrain construction in the Lead-Free forum,you
could have long term reliability concerns.
Some of the criteria we have for high reliability assemblies in a
potentially No-Clean(or low residue) soldering process is clean and
solderable parts/PWBs.Verifiable objective evidence of meeting these
requirements must be maintained and made available upon request.
Dewey
> -----Original Message-----
> From: Douglas O. Pauls [SMTP:[log in to unmask]]
> Sent: Wednesday, February 11, 2004 6:33 AM
> To: [log in to unmask]
> Subject: Re: [TN] Contamination on a SOT-23 component
>
> Good morning Daan,
>
> Where did you ever get that idea? Must have been one of those mornings
> before I had my Diet Dew(s).
>
> Residues on components or bare boards is always an issue. If the residue
> on either is a purely surface residue, then it is less of a concern if
> they
> are going into a no-clean assembly operation. It is more of a concern, or
> critical, in no-clean assembly because you have no way of addressing those
> residues.
>
> If the components or boards have absorbed residues, you are toast. You
> "might" be able to do rescue cleaning in mild cases, but most often not.
> The laws of physics are not subject to repeal or negotiation.
>
> Doug Pauls
>
>
>
>
>
> "d. terstegge"
>
> <[log in to unmask] To:
> [log in to unmask]
>
> SGROUP.COM> cc:
>
> Sent by: TechNet Subject: Re: [TN]
> Contamination on a SOT-23 component
> <[log in to unmask]>
>
>
>
>
>
> 02/11/2004 03:16 AM
>
> Please respond to
>
> "TechNet E-Mail Forum.";
>
> Please respond to "d.
>
> terstegge"
>
>
>
>
>
>
>
>
>
> Hi Brian,
>
> I understood from earlier posting of you and others that the lack of
> cleanliness of incoming components is considered a risk ONLY for
> no-clean technology. Now Cheryl obviously has a problem with
> contaminated parts in a process that does include cleaning. This makes
> me wonder how (in general) the chances are that a cleaning process
> designed mainly for cleaning flux residues from pcb assemblies will
> clean the variety of contaminants present on incoming parts. Perhaps you
> can comment on this ?
>
> Daan Terstegge
> Thales Communications
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
> >>> [log in to unmask] 02/11/04 08:56am >>>
> Amen! Lord Doug has hit it on the head.
>
> It may interest you (academically) to know that the erstwhile company
> I
> owned manufactured the Microcontaminometer 20 years ago, through to
> 1991. It was capable of measuring the ionic contamination on parts as
> small as a single diode. It was not a popular instrument: I think we
> probably sold less than 50 of the beasts. What we did find was that
> many
> components were hopelessly badly contaminated. There is a whole
> chapter
> in my book on this subject, with photos. One IC, which is shown,
> measured at 12.4 µg/cm2 eq. NaCl and this is by no means exceptional.
>
> My experience in my former professional life was that component
> manufacturers cared even less about cleanliness than they did about
> solderability and I know no reason why this state of affairs should be
> any different today.
>
> Brian
>
> Cheryl Tulkoff wrote:
>
> > I've been working on a tough but challenging contamination problem.
> The
> > contamination causes electrical leakage fails on a precision test
> > instrument. Ion chromatography analysis points to an incoming
> cleanliness
> > problem on a SOT-23 component. Elevated choride and sulfate levels
> were
> > found on the components (5x - 10x greater ug/in2 levels than
> anything
> > found elsewhere on the boards). High levels were found even on our
> "good"
> > boards.
> >
> > We are trying to work with our supplier to identify and fix the
> problem
> > long term but are looking for some short term fixes as well.
> Repeated
> > water washing of the boards (high pressure spray cleaning) improves
> the
> > situation but does not fix it. Alcohol scrubs in the area further
> improve
> > it but don't eliminate the problem entirely.
> >
> > We have a only a DI water wash process (no surfactant/saponifier
> > capability).Does anyone have any board or component cleaning
> > recommendations?
> >
> > Are there any parts makers out there willing to tell me a little
> more
> > about parts cleaning after the lead plating process?
> >
> > What tool(s) do part makers use to verify cleanliness of parts?
> >
> > I don't have a tool capable of measuring what was found on the part
> so I
> > don't know where to go.
> >
> > Thanks, Cheryl Tulkoff
> >
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