Hi Chris,
I hope you don't mind my diving into this question. We often recommend
somewhere in the 2-10 Megohm-cm range for deionized water assembly cleaning,
with 5-6 megohm being sort of the target. Keep in mind that there is no one
size fits all answer, as there are several "it depends" factors here. I am
assuming, based on your question, that you have not studied the effects of
varying the water resistivity. That being said, data is always king.
Perhaps doing some studies varying the water resistivity would give you the
answer you seek.
As for why you continue having cleaning concerns, could it be that deionized
water alone doesn't pack enough of a punch to get the job done consistently?
Residues are always a compilation of bare boards, components, and assembly
materials. Any variation in the consistency of their cleanliness and normal
assembly process variation can yield variations in the cleaning results.
Understanding those variations would help you better define what cleaning
parameters need to be tweaked to achieve a more robust and consistent
cleaning process.
Just my 2 cents.
Best Regards,
Joe Russeau
Process Analyst
Precision Analytical Laboratory, Inc.
----- Original Message -----
From: "Schaefer, Chris" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 05, 2008 11:43 AM
Subject: Re: [TN] Cleaning No-clean
Terry,
A little off the subject. How important do you think it is to use high
quality DI water as opposed to using 200K DI water in an Inline Aqueous
System? I typically use something in the range of 12-18Mohm DI water at a
minimum at the final rinse whether its a chemistry inline wash or purely a
water wash. We produce Class 3 product that requires zero residuals at
10-40X, with less than 10.06NaCl/ sq.in. ionics. The company I am currently
working for does not believe 10-18Mohm water is necessary, but we continue
to have cleaning issues that are caused by poor process, old chemistry, and
likely the water.
Any thoughts?
Thank You,
Chris - AKA Booker
Chris Schaefer
Suntron Corporation
Process Engineer
800 N. Brutscher Street
Newberg, OR 97132
Work Phone: 503.554.6270
Cell Phone: 785.248.9016
Email: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Terry L. Munson
Sent: Wednesday, March 05, 2008 8:22 AM
To: [log in to unmask]
Subject: Re: [TN] Cleaning No-clean
Dan and Brian
We have qualified clients who clean a no clean and have since the mid 90's
(Les Hymes was one of the first). But we have found that with a rescue
cleaning and only if you have water tolerant parts (if not those need to be
removed) that you can effectively clean a residue that was not designed to
be cleaned.
These residues do need a good saponifier, low pressure inline (not able to
do in a standard batch system), heated to 140-150 F wash and rinse with DI
water at 10 meg ohm or better, but this is not enough by itself but we
found that if we use DI steam after wash and before rinse then we are able
to clean under low standoff components, BGA's, and with a little help QFN
and PQFN
packages. We presented this information at the IPC Midwest Expo 2007,
authored
by Eric Camden. We have successfully been rescue cleaning for the last 7
years no clean assemblies that were 6-12 months old. So it is very doable
but standard batch cleaning with a saponifier has not proven to us or our
customers who we have help implement this type of cleaning that batch or
standard inline cleaning is able to do the job.
Terry Munson
Foresite
765-457-8095
In a message dated 3/5/2008 10:53:25 A.M. Eastern Standard Time,
[log in to unmask] writes:
"Generally speaking I have not seen good results in trying to clean off
no-clean flux. They call it "no-clean" for a reason."
Agreed!!! Even if you succeed to do the job well - it can be done with some
fluxes - it will not be very easy and may be quite costly. I have always
said, if you clean, use a flux which was designed from the start for easy
cleaning.
¤0.02 worth
Brian
Dan Mauro wrote:
> Folks,
>
>
>
> I have a need to clean No-clean residue from PCBA's. Can this be
> achieved with water washer and some type of saponifier ? Can anybody
> suggest a batch process?
>
>
>
> Thanks,
>
> Dan
>
>
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