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October 1997

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Subject:
From:
Doug Pauls <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Mon, 13 Oct 1997 09:57:07 -0400
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Good Morning Jan,

Since two of my compatriots seem to think I should comment on your questions,
I will.

>
>  I need a quick education.  The company I have recently hired on at,
>  would like to immediately change over from RMA flux to Water Soluble
>  flux for both SMT and thru-hole.  Most of our work is military. It has
>  been several years since I've researched this topic.

Hmmmm.  A change in flux technologies, together with issues of single process
initiatives and block changes for military contracts -- a quick education is
not possible.  You have chosen two very complicated areas.  This change in
flux technologies is more straightforward, since you are not dealing with
human behavior or the DFARS.  The second is, of course, a nightmare.

>
>  Are SIR tests still required to prove your cleaning methods?

It depends.  Each military customer is different.  Given the DoD mandate to
be "silent" on the issue of soldering, it makes it difficult to get a clear
response on what data must be provided to prove out a new process.  Since
MIL-STD-2000A is obsolete for NEW contracts (still applies to old contracts
in force), most military manufacturers are either going to J-STD-001B or are
doing their own process validation.  J-STD-001B has a process qualification
protocol which is exclusively SIR based.  This protocol is required for water
soluble fluxes.  Should SIR be required to prove out a new process?  In my
opinion, yes (big surprise there).  We might run a series of residue
characterization tests and debate endlessly on how much of a particular
residue is detrimental, but SIR testing can be used to show the effects of
the residues.  If it does not cause electrical leakage, metal migration, or
corrosion, then the residue is benign.

>  Are SIR tests only required for government contracts?

In my experience, no.  Many government contracts do require some form of
temperature-humidity-bias testing, but then many commercial contracts do as
well.  If a commercial house is qualified to J-STD-001, then they have SIR
data to back up their process (at least in theory).

>  Can Water Soluble fluxes be used on stranded wire?

Can they?  Yes.  Should they?  NO!  Stranded wire will pull flux residues far
up the bundle, and you are NOT going to clean it out or neutralize it
completely.  Count on corroded wires.  I have found flux residues a good
10-12" from the end of a stranded wire bundle.  The problem is capillary
action which draws the flux.  A number of specifications that I have reviewed
have taken the politically correct verbiage "water soluble fluxes can be used
provided the manufacturer has objective evidence to show that the flux is
fully cleaned or neutralized."  I don't buy it.

>  Which is a better cleaning process for Water Soluble flux, Batch systems
>  or in-line systems?

In my view, in-line.  I have yet to see a batch cleaner yield results
comparable to an in-line, all other factors being equal.  One of the biggest
problems I see is that in many batch cleaners, you get variable results.
 Boards from the center of the cleaner get clean.  Boards from the edges,
where water flow is less and cleaning impingement less, the cleanliness is
variable.  Throughput is less, cycle times are longer.  Those who do go to
batch cleaning are either "capital-challenged" or have a low volume anyway.
 For the former case, Marseco makes a relatively nice in-line cleaner (about
6' long) that seems to work well.

>  Have most government contractors switched to WS Flux or still using RMA?

Most?  Hmmm.  Hard to say.  I know most of the "big boys" have gone to either
water soluble flux with aqueous cleaning, RMA flux with saponified cleaning,
or gone no-clean.  The majority have gone to water solubles first, with a
goal of eventual migration to no-clean.  This is what I would recommend.
 Going from a military-RMA-clean paradigm to a no-clean process is not only a
huge technological jump, it is also a complete change in mindset and
corporate culture.  It is better to make the transition in two jumps rather
than in one big one, especially if time is of the essence.  If you do stay
with aqueous cleaning, I would strongly recommend using deionized water
throughout the machine, and a small amount of saponifier in the wash section.
 And to all you skeptics out there, it DOES make a difference.

>
>  Thanks in advance for all responses.
>

If you are interested, I have written two papers - Laymans Guide to
MIL-STD-2000A and MT-0002; and a second Layman's guide for J-STD-001B.  Both
examine elements of qualifying a new process.

Hope this helps.  You have a long journey through murky woods ahead....
 Lions and tigers and bears, oh my.

Doug Pauls
Contamination Studies Labs
765-457-8095
[log in to unmask]

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