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January 2012

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From:
"jrusseau.precisionanalysts.com" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, jrusseau.precisionanalysts.com
Date:
Mon, 9 Jan 2012 09:22:53 -0500
Content-Type:
text/plain
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text/plain (245 lines)
One thing is for sure the use of tap water can be a highly variable part of 
the equation for cleaning boards.  As Joyce pointed out, you have 
geographical variations in water quality, not to mention you have seasonal 
variations as well.  I think it would be hard to define an IPC spec around 
tap water quality used for cleaning, where it wouldn't be so much so using a 
specified resistivity or conductivity for DI water.  That's not say that tap 
water couldn't be used, but each company would need to evaluate the effects 
to product if choosing to use tap water cleaning, which leads me to my 
point.  Based on the original post, it sounds as though the company using 
the spot cleaning with room temp distilled water has not validated that 
their process is effective and reliable for removing the flux they're using. 
At the end of the day, process validation is a critical necessity.  Not 
validating the process might save a little money in the short run, but could 
cost you big long term.

I would suggest performing some ionic contamination testing on the samples. 
Perhaps you could compare between some that were cleaned and some that were 
not cleaned to assess how effective the cleaning process really is.  Also, 
if you have some boards that were processed with the 2331-ZX flux that are 
considered to be "good", you could also test them to determine if they are 
in-line with the other cleaned boards.  Further, should you consider sending 
boards for contamination testing, it would be advisable to send a couple of 
unprocessed samples to baseline you're starting cleanliness.  Ultimately, my 
guess is that the cleaning process you're using is highly variable at best, 
especially if they are spot cleaning.

Best Regards,

Joe Russeau

----- Original Message ----- 
From: "Robert Kondner" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, January 09, 2012 8:34 AM
Subject: Re: [TN] Cleaning water soluble flux‏


> Terry,
>
> You pooh-pooh tap water but failed to state two important parameters:
>
>  1. Dissolved content in tap water. Let's assume it is all ionic in 
> nature. (500mg / L Seems like worst case)
>
>  2. Amount of water that remains on a board (average per sq. inch) after 
> blow off.
>
>  I would love to see the results of a test as you propose. Let us not 
> argue like CAD Monkeys, let us do an experiment.
>
> I would ask that you weight the PCB after the final blow off of tap water 
> and then after a hot air dry, the difference being retained tap water 
> residue. I am very curious as to the weight of tap water contained on a 
> board after blow off. That should directly relate to final ionic residue 
> and water ionic content.
>
> I do not have a scale here that is sensitive to where I can measure the 
> difference. I hope you do.
>
> Does ANYONE on this list have a PCB, water, air gun, oven and sensitive 
> scale?
>
> Can anyone suggest a sensitive scale I can buy for not too much money? Is 
> so I will buy one and test.
>
> Thanks,
> Bob Kondner
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Terry Munso
> Sent: Sunday, January 08, 2012 10:51 PM
> To: [log in to unmask]
> Subject: Re: [TN] Cleaning water soluble flux‏
>
> I find it interesting that the use of tap water is still being proposed. 
> Let's look at the residues in tap water in industrial regions. High levels 
> of chloride, sulfate and and sodium and processing  through sand 
> filtration creating soluble silica globules that hold concentrated pockets 
> of contaminants.  This approached worked with rosin based fluxes in the 
> 90s.  But lets look at the level of circuit sensitivity of today's 
> hardware (where a half meg ohm drift will shut down a critical circuit and 
> maybe the entire system) and the effect of residues that are moisture 
> absorbing and conductive are creating performance problems. I propose that 
> we run a series of evaluations comparing tap water, to RO water to DI 
> water. Then i propose that we evaluate the results by ion chromatography 
> using both the C3 localized extractions and bag extractions of our Umpire 
> 2 SIR test board. Using the IPC SIR conditions of 40C/93% with continuous 
> monitoring to assess the residue effects. Oh yes it's true that the 
> resistivity drops to nothing but not due ionic contamination that is found 
> in tap water but the absorption of CO2 that has no residual effect on the 
> active circuitry. Oh and if you paid attention I suggested the the board 
> be rinsed with DI water steam and not tested in my lab so how much simpler 
> can that be.
>
> Terry Munson
> Foresite Inc
> 765-457-8095
>
>
> On Jan 8, 2012, at 8:11 PM, "Robert Kondner" <[log in to unmask]> 
> wrote:
>
>> Before you go through the expense and effort of doing DI to clean and
>> rinse try doing a tap clean and rinse WITH a blow off cycle. Have some
>> ionic contamination tests run afterwards, they will be very clean if
>> you have a good blow off.
>>
>> Washing with Di water is kind of silly, how long does Di water remain
>> DI after a wash of dirty boards start?  Maybe 100 ms? Wash with tap.
>>
>> Rinse in DI might help but a blow off of tap water leaves only tiny
>> amounts of material even with very hard tap water. It really depends
>> on water entrapment issues and then even a rinse is questionable.
>>
>> Try something simple and measure.
>>
>> Bob K.
>>
>>
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Terry Munson
>> Sent: Saturday, January 07, 2012 7:44 PM
>> To: [log in to unmask]
>> Subject: Re: [TN] Cleaning water soluble flux‏
>>
>> They should look at DI water steam to clean and rinse.  We have
>> effectively cleaned 2331-ZX flux. With stop steam cleaning. Call me at 
>> 765-457-8095.
>>
>> Terry Munson
>> Foresite
>> 765-457-8095
>>
>>
>> On Jan 7, 2012, at 6:36 PM, Gary Bremer <[log in to unmask]> wrote:
>>
>>> I am presently working as an contractor for the next few months then
>>> back
>> to unemployment, last place I worked was Jet Propulsion Laboratory on
>> the Mars Science Laboratory.  These are lighted panels for various
>> aircraft and the company policy is for J-STD-001/IPC-A-610 Class 3
>> The failure is with miniature T-1 lamps that stop working after going 
>> through an baking process.
>> Other boards that use these lamps but use RMA flux do not have this
>> problem, I suspect the cleaning process and the flux.  They do not
>> check ionic contamination and handle the boards with bare hands and
>> the operators even know when components are ESD sensitive or not.  I
>> have recommended they change the cleaning process to an Aqueous type
>> batch cleaner but this cost money which they do not wish to spend.
>> Their process person believes that their process is fine and something
>> else is causing the problem (bad lamps, forming lamp leads, etc.).  This 
>> goes against all my knowledge and training.
>>>
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