Amanda

Your last question first:
As a general rule, the higher the activation, the easier it is to solder with, but the
more active are the residues. You will also find, again as a general rule, that ionic
contamination is higher after soldering with a more active flux. This is why thousands
of users have come unstuck with "no-clean" fluxes: they choose the easiest-to-use (ie
to solder with) and to hell with what can happen afterwards. I know 2 large companies -
who should have known better - who have literally lost millions because of corroded
boards being returned because of this. If you want reliability with "no-clean", choose
your flux/paste VERY carefully, indeed. I know another large company that did do their
homework properly and tested 65 different "no-clean" fluxes - and qualified just two,
both of which were on the limit for one or two parameters. This company has been using
these two fluxes for several years now (with difficulty for soldering) in several
factories and have had no in-service problems or returns ascribed to the fluxes, even
under poor climatic conditions.

Did you do all the SIR tests simultaneously? If so, cross-contamination is a
possibility: some of residues may sublime from one board and be deposited on another.

Brian

"Amanda.Mountain" wrote:

> Hi all.  I'm hoping to pull on the experience on this list...
>
> Performing a flux evaluation, we performed SIR tests with 8 different
> conditions (4 fluxes, 2 temperatures).  The IPC coupons were processed
> through our wave soldering/spray fluxing process, doing our best to simulate
> regular production.  The fluxes we are evaluating are all VOC free/no
> clean/water soluble/low solids/low residue fluxes.
>
> The test was performed to Bellcore standards.
>
> The SIR results we received were lower than expected - ranging from 2.74E+9
> to 4.27E+10.   The pass value assigned by the laboratory is 3.2E+10.  Only 3
> of 32 samples actually passed this standard.  6 of the 32 samples passed the
> Bellcore minimum value (2.0E+10).  What sort of implications can we expect
> with selecting a flux with slightly lower SIR results than the minimum
> value?  Each of the flux vendors provided their own passing SIR test
> results.
>
> One other thing that was noted was that the boards with the fewest defects
> came back with the poorest SIR results, and vice versa.  Is this just a
> coincidence, or is there a solid explanation for this?
>
> Thanks in advance,
>
> Amanda Mountain
>
> Amanda Mountain
> Process Engineering
> Leitch Technology International Inc.
> Phone: (416) 445-9640 ext. 3852
> Fax:  (416) 445-7927
> http://www.leitch.com/
>
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