Hi

hmmmmmmmm, Diet Dew. This is a new one on me. What have I been missing
out on here?

Thanks for your response Doug.

I also have noticed that final CCA cleanliness level varies with
placement of the card in the batch washer.

I guess what I need to do at this point is determine what kind of
residue I am dealing with here. I understand that the rosin in the flux
is non-ionic. It is the activators that pose the danger and it is the
activators that show up as ionic residues. I'll run some tests to see if
the residues are ionic.

In parallel to this, Im am investigating some alternate cleaning
chemistries. We have been using our existing saponifier chemistries for
many years now. Maybe there is something out there that will do a better
job of cleaning under SM components.

We have no evidence of units failing after stress testing due to
cleanliness issues. However, we have seen that vibration testing does
dislodge some of the white residue from under SM components.

Regards,
Virgil



[log in to unmask] wrote:
>
> To answer your question - how clean is clean enough:
>
> Your assemblies are clean enough, when they function in the end-use
> environment with the stated MTBF of the product or for the design life of
> the product, with no failures attributable to electrochemical failure
> mechanisms.
>
> There, now that we have solved that burning question for the industry,
> let's go do lunch
>
> <Hmmmmmm, dum de dum de dummmmmm>
>
> Oh, you would like to know how this is done?  Wouldn't we all!!!!!!!
>
> First you have to understand electrochemical failure mechanisms.  Then you
> have to understand your end use environment.  Then you have to understand
> how your material sets interact in the end-use environment.  Then you have
> to understand residue classification and quantification.  Then you have to
> understand how residues affect end item performance.  Then (and you should
> be approaching retirement by now) you have to correlate the results of the
> residue assessment with the life predictions from accelerated stress tests.
> Once you have done all this, then you will have the beginnings of wisdom
> and understanding of how clean is clean enough.  Then you go retire to
> Cyprus and raise oranges, or kumquats, or figs, or whatever Brian grows
> these days.
>
> To bring myself down from a Diet Dew crazed haze:
>
> The white residue that you are seeing is most likely abietic acid from the
> RMA that did not get cleaned off in the batch cleaner.  I have found that
> assemblies at the outer portion of a batch cleaner do not get as clean as
> those in the inner portion.  Most of the time when I have seen white
> residue from an RMA, it is harmless and is more of a process indicator.
> But, that all depends on how much activator is retained in the white
> residue.  Another possible drawback is that it may be an amalgam of
> residual flux and cleaning agent.   How do your assemblies do in
> environmental stress testing.
>
> If you go back through the Technet Archive, search on either my name or
> Brian Ellis'.  We have talked about this topic numerous times in the past.
>
> Doug Pauls
> Advanced Operations Engineering
> Rockwell Collins
>
> P.S.  Have flipped 23 matches into a bucket of Diet Dew and so far, no
> explosions.............
>


--
Virgil Lenton - Manufacturing Engineering
SED Systems - A Division of Calian
Saskatoon, Saskatchewan
Canada

Web: www.sedsystems.ca     email: [log in to unmask]

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