This is good advise for highly active [low pH] liquid fluxes, but Joel is
asking about lead free solder paste.
The activity level in WS solder pastes is much lower, closer to ordinary NC
types.
[If the flux in paste were active enough to attack solder it would chew up
the powder in the jar, making the paste useless].
Well formulated water wash pastes are able to take a delayed wash cycle
permitting cleaning to take place after a couple of reflows (one each side)
or post reflow component attach and repair, thus allowing a single wash
after all assembly.
Regards
Mike Fenner
Indium Corporation
T: + 44 1908 580 400
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: 19 January 2006 08:50
To: [log in to unmask]
Subject: Re: [TN] Time before Cleaning WS Flux
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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