Craig
Polyethylene glycols were identified c. 1979 by the long-regretted Frank
Zado to cause a potential drop of insulation resistance. Jack Brous and
Bob Turnbull of Alpha did some further research on the phenomenon and
published a paper showing that different PEGs and other glycols and
derivatives had very different effects, the high MW PEGs being worst and
some being practically harmless. The mechanism was a combination of two
phenomena, the opening of pores on substrates at temperatures > Tg and
the lipophilic "ends" of molecules hydrogen-bonding with material in the
pores, which then trapped them in, leaving the hydrophilic ends exposed
to attract water (graphic description): I think I was possibly among the
first to hypothesise this, which was later confirmed by others.
It is a pure electrical problem, not a question of corrosion, although a
drop of SIR can aid this, as well. (I prefer a drop of Doug's Mountain
Dew).
Brian
Craig Hillman wrote:
>
> Technetters,
>
> I want to thank Andrews, Brian and Doug for their feedback on wetting
> agents. I would like to stir up just a little more discussion on this issue.
>
> I have seen indications that for flux to be on a military qualified products
> list (QPL), it should be halogen and polyglycol-free. Based on some
> discussions I have reviewed, this could be because polyglycol, or "bad"
> polyglycol, can lead to an increase in current leakage on assemblies.
> However, has anyone come across experimental evidence that polyglycol, or
> other wetting agents, can greatly accelerate corrosion of eutectic solder?
> Trying to see if my testing is out of wack or if I'm measuring a real
> mechanism.
>
> Best Regards
> Craig
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
> Sent: Friday, August 17, 2001 4:59 AM
> To: [log in to unmask]
> Subject: Re: [TN] Wetting Agents
>
> Craig
>
> There are many. However, I'd like to warn you against some of the
> non-ionic polyethoxylates (heptyl-, octyl- nonyl- etc.), whether linear
> or cyclic, especially as a component of water-soluble fluxes. These
> biodegrade rapidly but form an extremely persistent series of virtually
> unbiodegradable by-products which are highly toxic to aquatic life. The
> sale of such surfactants is regulated in some countries but things like
> fluxes which contain them are available.
>
> Best regards,
>
> Brian
>
> Craig Hillman wrote:
> >
> > Hello Technetter,
> >
> > Quick question: What are some of the common chemicals used as wetting
> > agents/surfactants in fluxes?
> >
> > Thanks for your help,
> > Craig
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Furrow, Robert Gordon
> > (Bob)
> > Sent: Wednesday, August 15, 2001 2:31 PM
> > To: [log in to unmask]
> > Subject: [TN] FMA Labs in Northeast US
> >
> > Hi All,
> >
> > With the drastic reduction occurring here at Lucent, I am going to be
> > without the services of our Evaluation / FMA Lab in Princeton for (at the
> > very least) the period it takes to relocate it. At the worst, it could be
> > shut down altogether. I am looking for another source to do the testing of
> > PWB's and Backplanes for conformance to our specifications and reliability
> > needs. This testing includes cross-sectioning with analysis, XRF, thermal
> > shock, pull tests, solderability evaluation, SIR/EM, SEM/EDX, and also FMA
> > of assembled boards. Ideally, I am looking for someone within driving
> > distance so that I can easily foster the relationship. However, I am open
> to
> > any viable suggestions. If this is a testimonial from users please respond
> > via the TechNet. If this is a lab promoting its capabilities, please
> contact
> > me directly at [log in to unmask] Thanks in advance for everyone's input.
> >
> > P.S. I am also looking for a lab to provide me the direction, insight,
> > foresight, enthusiasm, and overall experience that George Wenger at our
> > Princeton Lab has provided me.
> >
> > Thanks,
> > Robert Furrow
> > Printed Wiring Board Engineer
> > Strategic Supply Global Account Manager
> > Supply Chain Networks
> > Lucent Technologies
> > 978-960-3224 [log in to unmask]
> >
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