Pat,
"all electrolytic caps etc. are replaced every other cycle" Please explain
the definition of "cycle" in this context.
Bev
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Goodyear, Patrick
Sent: Tuesday, April 24, 2012 11:13 PM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux
Mike I forwarded this to the group. I supposed this is what you ment by a
thought out process.
One of the "NICE" things about working in the Nuclear industry is everything
we do is proceduralized and must be performed by Qualified workers, workers
who are tested and evaluated annually on their skills and knowledge, so we
have a luxury there. All of our safety related equipment regardless of
manufacturer is inspected prior to installation to 0 defect, this means in
most cases better than IPC Class 3, someone must sign on the dotted line to
"accept" Class 3, and the engineers aren't willing to commit. We also
perform full inspections on a 3-5 year cycle so each piece of safety related
equipment has a teardown inspection every few years, all electrolytic caps
etc. are replaced every other cycle. Backup batteries are replaced every
other year regardless of their usage. On certain instrumentation (seismic
for instance) batteries are load tested every 6 months in addition.
We have tried 190 & 200 proof denatured, but they leave residues behind.
Then again we don't have to sell a product for the lowest price.
Hey, it keeps me in toys.
Pat
-----Original Message-----
From: Mike Fenner [mailto:[log in to unmask]]
Sent: Tuesday, April 24, 2012 8:13 AM
To: Goodyear, Patrick
Subject: RE: [TN] No-Clean Flux
Yes but you are using a thought out process and the people we are talking
about are not.
Further comment:
When I say alcohol I mean IPA or flux thinner. I am not a great fan of
alcohol/IPA as a cleaner, and certainly tests done years ago by BAe at the
time of search for Freon alternatives resulting from the Montreal protocol
didn't demonstrate it was effective as other alternates. They were using hot
(boiling) IPA in a great big machine so far as I recall. Ethanol would be
more polar and I think has higher solvency as well. YOU just have to be
seriously rich and on good terms with whoever controls these things in
licensing terms.
OTOH, people have been using Isopropanol, methanol etc for years. So clearly
it works well enough for some. If you are not getting failures and meeting
cleanliness requirements laid down then you are cleaning well enough.
People like me tend to speak in absolutes and forget to say we are talking
theoretical best. Process A may well not be as good as Process B and there
are hazards associated with doing process C, however these are absolutes.
Anyone one of them may be good enough. Why go for 120% or 90% when you need
70% to achieve reliable design life? You're just adding cost by over
specifying materials or process.
Perfection is rarely needed, good enough is good enough.
Years ago I was asked to help on a project to reduce the cost of MIL
computers. Essentially they were a Ceramic and gold plated PC meeting all
sorts of MIL every step of the way. I was brought in because they were 3x
the price of a consumer unit and customer wanted to pay only 2x.
Customer had spent six months on cost reduction programme and cheese paired
price 10% and making no money before calling me in. My suggestion was to
think on lines "buy one a commercial type and spend as much as you like [up
to doubling the price] on Militarizing it".
Actually after 6 months of analyzing failure modes in ALT we implemented a
programme achieving as good or better reliability on final units. This cost
about $10 for additional spot conformal coating (Plus another $100 on
thermal management and packaging), So the cost was actually reduced by about
80% and the price to customer "met the target" = smiles and nice profits all
round.
Regards
Mike Fenner
Bonding Services & Products
T: +44 [0] 1865 522 663 E: [log in to unmask]
-----Original Message-----
From: Goodyear, Patrick [mailto:[log in to unmask]]
Sent: Tuesday, April 24, 2012 1:11 PM
To: [log in to unmask]
Subject: RE: [TN] No-Clean Flux
Mike,
Will the use of Alcohol as the cleaner adequately remove any residues? We
typically use 200 proof as the cleaning agent, easier to spot control it's
use.
Pat Goodyear
Control Technician
PG&E
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Tuesday, April 24, 2012 2:26 AM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux
Just a few additional small points for completeness.
Most low residue no clean fluxes are - as said - usually intended to be
de-activated by the heat of soldering. This would be the case on wave
soldering, but not hand where heating is very local. Any residues that have
not been heated by the repair iron are a cause for concern. Firstly because
they remain active as supplied. Second because the alcohol based types can
also dissolve into and change any no clean paste residues. (At 2, 3, 4 etc
percent solids they are essentially dirty alcohol (cleaner) in this respect.
So flooding the work area with them, though common is not best practice.
Casual use of local cleaning sprays is likely to just disperse them further
rather than remove them. The board just looks clean. The cleaner needs to
drain off the board before drying.
Over fluxing and poor cleaning are both common causes of in-service failure
and often overlooked.
A touch up pen might be a better technique for controlling flux application.
Some suppliers have specialized repair fluxes formulated to meet SIR before
and after soldering which does address this issue, but not if improperly
cleaned as the residue chemistry is again disturbed.
Regards
Mike Fenner
Bonding Services & Products
T: +44 [0] 1865 522 663 E: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Monday, April 23, 2012 6:37 PM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux
The acids you are talking about are not strong acids, but are also often
more reactive than many strong acids (ie: Form insoluble salts) and the
correct choice of resin in the column can insure rapid removal of the acid.
Rudy Sedlak
RD Chemical Company
--- On Mon, 4/23/12, Robert Kondner <[log in to unmask]> wrote:
From: Robert Kondner <[log in to unmask]>
Subject: Re: [TN] No-Clean Flux
To: [log in to unmask]
Date: Monday, April 23, 2012, 8:46 AM
Karen,
OK thanks.
One more general chemistry question:
If you have weak acids in solution, and you pass that solution through a DI
column, will the weak acid be removed from solution as quickly as a strong
acid?
Thanks,
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen
Sent: Monday, April 23, 2012 11:32 AM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux
The acids in no clean fluxes are usually sparingly soluble in water,
particularly adipic. The pH paper is a qualitative test. Spraying
phenolphthalein on .the board will contaminate it and the board will need to
be cleaned even if excess acid is not found.
If you want a quantitative test, use IC. There are ways to extract small
areas if you want to look for localized contamination.,
Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069
Re: [TN] No-Clean Flux
Robert Kondner
to:
TechNet
04/23/2012
11:10 AM
Sent by:
TechNet <[log in to unmask]>
Please respond to rkondner
Karen,
Thanks. Are these acids soluble in water? Can a collection of rinse water
be used to determine the "Quality" of the heating process?
Kind of like a simplified ionic contamination test? Maybe a rinse with a
basic phenolphthalein solution (pink) and if it turns clear "You Have Acid".
Is there any way to calculate if such a test would have sufficient accuracy
in the range of interest?
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen
Sent: Monday, April 23, 2012 10:52 AM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux
pH paper slightly dampened with DI water. I've used it and it works.
Some of the organic acid activators will be left behind after soldering, but
most of them should have sublimed during processing. Additionally, some
organic acids are worse than others; malic is worse than succinic is worse
than adipic.
Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069
Re: [TN] No-Clean Flux
Robert Kondner
to:
TechNet
04/23/2012
10:43 AM
Sent by:
TechNet <[log in to unmask]>
Please respond to rkondner
Hi,
Are there any spray on chemical indicator that can be used to detect for
activated flux? Something like a litmus or phenolphthalein solution?
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Monday, April 23, 2012 10:28 AM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux
I agree 100% with Doug. The important point is to ensure that the carboxylic
acids are sublimed. This starts to happen at temperatures around 180°C but
it takes time as well as temperature. It is therefore essential to limit the
quantity to the minimum necessary to do the job and confine to the joint
area. What is positive is that soldering irons operate at a higher
temperature than wave or reflow, so that residues that spread outside the
joint area will probably be heated sufficiently to ensure sufficient
sublimation. Another important point is to ensure that all the alcohol has
evaporated before starting the retouch, so that the latent heat of
evaporation would otherwise cool down the flux and allow it to spread before
sublimation takes place. This requires the operator to wait a few minutes
between dosing the flux and picking up the soldering iron. It is common to
have a row of fluxed assemblies and, as one is added at one end, a circuit
is picked up at the other end for soldering. I don't know whether it is
still available, but a flux with a crimson dye showed where unheated flux
was applied and was quite common in days of yore. The dye sublimated with
the activators.
Brian
On 23/04/2012 16:42, Woolley, Mark D. (Mark) wrote:
> I have an issue with one of the assembly houses we use. They are
> using a No-clean flux that contains adipit and succinic acids (per the
> MSDS) in an alcohol base.
>
> Is it allowed to leave flux on the PWB that HAS NOT BEEN DEACTIVATED
> BY HIGH TEMPERATURES OF SOLDERING?
>
> I am not talking about the flux used in the solder paste or wave
> soldered flus. I am talking about the flux used at rework and
> touch-up of the PWB.
>
>
>
> I havce seen papers detailing corrosion on PWBs using "no-clean"
> fluxes and I have seen it on some of our products. This usually
> pccurs near the periphery of the PWB where the wave solder flux is
> protected by the pallet used to pass the PWB through the solder wave.
>
>
>
> Any opinions and references will be appreciated. I can give the
> manufacturer and flux type to individuals, but don't want to put it in
> a global email.
>
>
>
> Thanks
>
> mark
>
>
>
>
>
> mark
>
> Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
> Westminster, CO 80234 USA |
>
> Voice (Lab): (303) 538-2166 | email: [log in to unmask] |
>
>
>
>
> ______________________________________________________________________
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