As a general rule, water-soluble flux residues are very dangerous. They
are usually very acid and can attack metals on the assembly. At the best
they will make the solder joints matt. At the worst, increasing quantity
of the residues will form adsorption bonds with the substrate and
components within the residues may polymerise, making it
quasi-impossible to clean the residues after, say, an hour or so. It
therefore is **very** necessary that cleaning be started within minutes
of soldering. However, there is an excellent work-around that has been
proven and that can extend the hold time before cleaning to a few hours,
the use of a chelating neutraliser. Many flux manufacturers offer these
under trade names such as Neutralizer 2051, Rinse-Aid and so on. They
are mildly alkaline, buffered, room-temperature, dilute baths (pH
typically 8.5 to 9), which must NOT be confused with saponifiers, which
are unsuitable for this job. They serve many functions, but the
assemblies can stay therein, immediately after soldering/reflow, from 2
minutes up to, say, 4+ hours. They will actually improve the cleaning
quality at almost no cost. The assemblies should be cleaned within
minutes of their removal from the holding tank. The makers usually
recommend a 5% solution of the concentrate, but a 2% solution has been
proved equally effective.
You can see this technique being used on the old video at
http://www.protonique.com/video/ in the context of wave soldering.
Brian
Joel Mearig wrote:
> I am currently using a water-soluble, lead-free solder paste from Kester. I
> am trying to minimize the cleaning cycles so I leave flux on the product for
> an extended period of time. Do any of you have any recommendations on the
> amount of time flux can be left on the product without affecting the
> cleaning process? Thanks in advance for your input.
>
>
>
> Joel Mearig
>
> Delta Tau Data Systems, Inc.
>
>
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