Pat
I would agree with you, but only up to a point. I think it is a little sweeping to
imply that ALL OA fluxes on ALL substrates will do as you say. By carefully choosing
the correct chemistry for the substrate, it is not necessarily as bad as you imply. I
have done extensive trials over the last 25 years and I can say categorically that with
some substrates, the situation can be measurably worsened with the use of saponifiers
which can cause many epoxy and, especially, polyimide substrates to swell and absorb
ionic contaminants like a sponge. As for their use on aqueous-developed PI solder
masks, it is at your risk and peril.
I agree that those OA fluxes which contain PEGs can cause the problems you describe,
but there are many, today, that do not.
On the other hand, I do recommend the use of a hold bath containing a weak solution of
a chelating neutraliser. These generally are buffered at about pH 9 (as opposed to 11 -
12 for saponifiers) and are generally beneficial without causing resin-swelling, not
even on dry film masks. The chelation ensures excellent solubilisation of all the heavy
metal salts. I have had customers use these for over 25 years for portable professional
equipment for use in all climates, without any problems. The return rate has been
negligible.
Typical ionic contamination levels when such PCBs are correctly cleaned is within the
range of 0,1 - 0,3 ug/cm2 eq. NaCl, which is about an order of magnitude better than
most of the old and existing standards.
Hope this puts the church back into the middle of the village.
Brian
Pat Kane wrote:
> Douglas
>
> Our evaluations of cleaning OA fluxes with DI water only, has shown that
> there are still corrosive residual levels of contaminants left on the
> surfaces of the PCB. These corrosive residues have direct impact on field
> performance of your product. When the DI water is heated, the levels do
> decrease slightly but the residues are still present at levels that pose a
> risk of electromigration and field failures. The addition of a saponifier
> substantially reduces the residues to acceptable levels. Many people have
> added heating systems to the DI water and attempted to eliminate the
> saponifier as a cost reducing measure, only to find the resulting cleanliness
> levels are too high and the product is at risk for field failure.
>
> Generally, we recommend a customer evaluate the cleaning process by
> performing a baseline assessment of their current activity before any changes
> are made in the cleaning process or flux selection. This gives a reference
> point to evaluate the impact of subsequent changes. Evaluations with
> customers have shown that the combination of hot DI water in addition to
> using a saponifier have proven to be the best at removing processing residues
> to acceptable levels. Subsequent evaluation can be made at this point to
> determine the concentration level of saponifier required in your process to
> achieve adequate cleaning.
>
> Hope this helps. If you need more information, please contact me off line
> for more information.
>
> Regards,
>
> Pat Kane
> Technical Sales Manager
> Contamination Studies Laboratories
> 765-457-8095
>
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--
Brian Ellis
Protonique SA
PO Box 78
CH-1032 Romanel-sur-Lausanne, Switzerland
Voice: +41 21-648 23 34 Fax: +41 21-648 24 11
E-mail: [log in to unmask]
URL: Technical and consultancy divisions:
http://www.protonique.com
Web services division:
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