So purified water is furypied? I've missed something, thought DI was more or
less neutral as there are no free metal ions, but only H2O
molluscs...hmm...molecules (don't speak pH). I can understand if hot water
is different, because then the atoms spin more and perhaps H2O molecules can
loose an oxygen electron or two to another level. Can you explain little
closer about this furypie acting? Comprendo nada.
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Brian Ellis
Skickat: den 7 mars 2008 15:57
Till: [log in to unmask]
Ämne: Re: [TN] Effects of rinsing with high purity water.
We didn't have the weld problem with our cleaning machines, as the
welding rods were 18-8-2-1 alloy (expensive but was chosen for that
reason).
Welding 18-8 or 18-8-2 (or lower Cr/Ni SS) with 18-8 (or lower Cr/Ni SS)
rods is a sure fire way of having the weld problem.
However, we had one customer who coupled the machine to the water from
their semiconductor plant and the 18-8-2 alloy of the sheet metal
developed a thin coating of a loose very fine red powder, known as
rouge, despite the molybdenum. See
http://www.corrosionlab.com/Failure-Analysis-Studies/rouging.htm for
more details. This caused a long-lasting complaint from the customer but
I kept telling him to use a less pure water.
We never saw this with other customers who used DI water from a
mixed-bed column.
Brian
Douglas O. Pauls wrote:
> Along these lines, but slightly different, when my esteemed colleague, Jim
> Maguire, formerly of Boeing, now with Intel, was doing SIR testing at
> Boeing, he told me an interesting story. All of their SIR chambers had
> been plumbed with 18 megohm-cm water to make it as pure as possible. After
> a while (don't remember the time frame) he started seeing very fine metal
> needles on his test samples. The high purity DI water had attacked the
> stainless steel of the chambers and the needles resulted. He had them
> plumbed with 8-10 megohm-cm water thereafter.
>
> I know that ultrapure DI water is not desired for use in microelectronics
> because it can attack aluminum bond pads, interfering with wire
> bondability. In most cases, a microelectronics facility may start with 18
> megohm water, to get out the impurities, but will then mix carbon dioxide
> back in to bring the resistivity down to the 2-6 megohm-cm range.
>
> For the cleaning of circuit boards, yes, I imagine that some people have
> been able to clean with tap water. Keep in mind that what comes out of
> the tap in your area may not be the same as what comes out of mine. Tap
> water quality varies greatly as you move geographically. My biggest
> problem with tap water cleaning is that most industrial water supplies are
> coming from the municipal water supply. They add chlorine and sulfur
> compounds to cut down on bacteria growth. What two ions are death to
> electronics? Sulfur and chlorine. That is why I have always recommended
> that people at least use RO quality water (500 kilohm-cm or higher) in
> cleaning electronics. If you are using a saponifier, as we do here, tap
> water has a large load of minerals that reduce the effectiveness of the
> saponifier and can result in shorter saponifier bath life. Again, with RO
> or DI water, I improve cleaning efficiency and extend chemical life which
> is more cost effective.
>
> On the other side of the coin, I have never really seen the need to have
> the ultrapure (15-18 mgeohm-cm) water for cleaning either. Purity of 2-8
> megohm-cm resistivity is easily achievable with standard industrial DI
> column setups.
>
> Doug Pauls
> Rockwell Collins
>
>
>
>
> Richard Kraszewski <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 03/07/2008 07:20 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Richard Kraszewski <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> Re: [TN] Effects of rinsing with high purity water.
>
>
>
>
>
>
> I've heard the reason is that high purity water is a rather unstable
> substance and as such is "ion hungry".
>
> Recall a story (urban "technet" legend?) which recounted how years ago
> Wang (?) had a custom SS cleaning system that used ultra pure DI. Over
> time the welded seams were eaten away and the system dumped on the
> floor.
>
> Rich K / Kimball
> 847-621-7310
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> Sent: Friday, March 07, 2008 4:27 AM
> To: [log in to unmask]
> Subject: Re: [TN] Effects of rinsing with high purity water.
>
> I'll offer you a guess, without any scientific knowledge to back it up.
> If the Au is porous, the Ni could be attacked with OA residues diluted
> during the first wash, leaving nickel halides in the pores. The high
> surface tension of the final rinse water may prevent them from being
> removed but the Au/Ni couple with the damp residues could make a nice
> corrosion cell. Plausible?
>
> Brian
>
> Peter Barton wrote:
>> Hello Technetters,
>>
>> There has been some comment on this forum recently implying that
> cleaning or
>> final rinsing of assemblies with high purity DI water can have a
> detrimental
>> effect on solderability. We very occasionally see a solderability
> issue when
>> processing second side surface mount after first side population and
>> cleaning. Because of product build times and the use of paste with an
> OA
>> flux that must be cleaned soon after soldering we have to wash the
> first
>> side before continuing with the second side.
>>
>> The surface finish of the PCB concerned is ENIG. We have had various
>> analyses carried out on the surface finish but have never had any
> conclusive
>> evidence that the finish itself contributes to the problems seen.
>>
>> Can one of the gurus please explain how high purity water could affect
>
>> solderability and, if there are any circumstances in which variation
> in ENIG
>> could be susceptible to degradation in solderability if cleaned this
> way.
>> Best rgds,
>>
>>
>>
>>
>>
>>
>>
> -----------------------------------------------------------------------
>> Peter Barton
>> Senior Process Engineer
>> ACW Technology Ltd
>> Dinas Isaf West
>> Tonypandy
>> Mid Glamorgan. CF40 1XX Wales
>>
>> Tel: 01443 425275 (direct)
>> Fax: 023 8048 4882
>> International Tel : +44 1443 425200
>> International Fax : +44 23 8048 4882
>> Website/URL: www.acw.co.uk
>>
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