My apologies for being about to point out what perhaps to you is obvious,
but it's not clear if you are going from

- RMA with no cleaning
- RMA with solvent cleaning
- RMA with semiaqeous cleaning

IF you are already semi-aqueous cleaning it's a small step to 100% water
wash and you end up with a simplified process.

IF you are not presently cleaning this is a big step you are proposing. Even
from solvent cleaning it's a significant change as water is very different
in its behaviour from solvent. [Basically it doesn't want to be dry and its
higher surface tension  makes for different behaviour.] In this case the
last thing to worry about is process validation/control.

You have to make sure that your assemblies can be water washed:  components
are sealed, no water traps caused by geometries of board and components, no
sleeved wires, gaps under devices can be flushed though and so on. Can
assemblies stand drying cycle and so on. Even things like labels not being
water proof can catch you out.



Regards

Mike Fenner
Indium Corporation

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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: 22 November 2005 14:35
To: [log in to unmask]
Subject: Re: [TN] Water Soluble Flux

You qualify it initially by SIR/ECMR testing, possibly IC analysis. Once you
have qualified the product and the process, you can then test a number of
identical assemblies in an ionic contamination tester to establish a process
control baseline (mean and standard deviation) for that type of assembly. If
subsequent production testing falls into the same mean and standard
deviation envelope, you can go to bed at night and sleep soundly on both
ears. I recommend this qualification be repeated, say, annually, to cater
for variations.

Brian

Long, Thomas - Avionics wrote:
>         I am looking for some advice on qualifying a process for
> switching from RMA flux to water soluble flux.  I am aware that a
> large company learned through SIR testing (too late) that when
> switching from RMA to water soluble their cleaning process was not
> effectively cleaning all of the flux residues off and it was causing
> performance issues.  The company actually had to scrap product and
> revisit type of flux and cleaning.  I'm not sure if organic flux
> residues can be detected with omegameter cleanliness testing and this
product is class 3 high rel.
>
>         I appreciate any input and experiences that anyone can share.
>
> Tom Long
> ITT Avionics


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