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April 2012

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Subject:
From:
Paul Edwards <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Edwards <[log in to unmask]>
Date:
Thu, 26 Apr 2012 07:09:58 -0700
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It would seem that it is all a matter of critical failure risk assesment properly applied...
We always find the burnt wiring or blown cap after the house is burnt to the ground...
I'll bet that some people in Japan wish they had built a 15m higher seawall...

Paul

Paul Edwards
[log in to unmask]
Surface Art Engineering


Phil Nutting wrote:

Holy cow!  And this makes nuclear power less expensive?

Don't get me wrong.  I'm all for nuclear safety, but I'm what you call a "frugal yankee".  If it isn't broken, don't fix it unless it clearly needs to have more cool engineering features.  The parts removed would go "into stock" for a future project.  Never know when you might need one or two of those.

That is how I build a lot of stuff around here (you can rest assured not in production stuff), by using castoff or unused parts.

It's no not that I don't have two nickels to rub together, I've just worn them out.

Phil the Frugal

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Goodyear, Patrick
Sent: Thursday, April 26, 2012 12:14 AM
To: [log in to unmask]
Subject: Re: [TN] No-Clean Flux

Cycle in this context is inspection cycle so every 6-10 years we change out all electrolytic caps depending on equipment safety importance.  The other thing is batteries, and non-volatile ram gets changed each refuel.  Refuel cycles are 20 months, every other refuel we inspect a given instrument set.   We have 4 instrument sets so each refuel outage we inspect a pair of instrument sets and change caps etc.    The other number comes from the instrument sets where we have 3 set redundancy and skip two refueling cycles, so those are every third refuel, i.e. one set each refuel.

As I said keeps me in toys.
Pat

-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Wednesday, April 25, 2012 5:22 PM
To: 'TechNet E-Mail Forum'; Goodyear, Patrick
Subject: RE: [TN] No-Clean Flux

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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