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November 2005

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From:
Kevin Glidden <[log in to unmask]>
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Date:
Fri, 4 Nov 2005 08:11:49 -0500
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I have also heard that IPA can crystallize and/or harden rosin flux
residues, making them MORE difficult to remove.  Is this true as well?
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Friday, November 04, 2005 4:34 AM
To: [log in to unmask]
Subject: Re: [TN] compressed air

On request. Even 99% IPA has sufficient impure water in it to have a finite
conductivity. To make up the Contaminometer solutions in a past life, I used
pro analysi 99.9% reagent grade but I still had to deionise it before mixing
with water at <0.06 µS-cm (so-called 18 meg water), to ensure minimal ionics
before packing (note I didn't deionise the mixture). Of course, the
conductivity rose after packing, in PE containers that had been soaked for
24 hours in similar solution, as the solution will absorb CO2 like
gangbusters.

The upshot is that IPA does contain unspecified ionic impurities which will
be deposited in small quantities after evaporation. The downshot is that I
believe these may be harmless in most circumstances with 99% IPA or purer.

However, the unspecified contaminants that will be spread over the assembly
with an IPA wash MAY be sufficiently ionic to be dangerous. IPA is NOT a
good idea but, if it were to be used, it must be followed by a DI water wash
and rinse to ensure adequate removal of residual ionics, especially when the
history of the returned goods is unknown (they may have been used near
stormy seas or salted roads, for example). As you have to wash, anyway,
better just to wash with a suitable detergent and forget IPA which is
flammable (flash point ~12°C), volatile and toxic (TWA OEL 400 ppm in many
countries).

Brian dixit



Barbara J. Rich wrote:
>   
> 
> I am looking for any information on using compressed air to blow off 
> "dust bunnies" on circuit boards coming from the field.
> 
>  
> 
> Barb Rich
> 
> Admin. Support Mfg.
> 
> Sanmina-Sci
> 
> 321 S. Taylor Ave.
> 
> 303-264-2009
> 
>  
> 
> 
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