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August 2007

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Subject:
From:
Rob Strecker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rob Strecker <[log in to unmask]>
Date:
Tue, 14 Aug 2007 08:29:59 -0600
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Thanks for your responses,
Does this mean that combining different flux chemistries will not contribute to foaming?  Is there enough flux left over on the boards from SMT to be a major contributor to foaming?  Just to clarify, we are on the low sided of our wash temperature, we are not currently using a defoamer or saponifier, just pure DI water.  We have also seen foaming during the first wash load with a fresh water change out.  How important is it to have our wash tank completely clean of all previous wash residues before we refill with fresh water?  Can minimal residues cause major foaming in the next wash?  Purchasing a defoamer at this point is not an option, it will be used as a last resort.  We have a run coming up that we will be separating and washing SMT boards pre-wave and washing them again post-wave then washing the last batch after it's been through both processes (worst case) all with fresh water.  What are some of the risks associated with board wash foaming?  If some foaming residue is left on the boards what would they look like and what problems could they cause, if any?

Thanks
Rob Strecker 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Tuesday, August 14, 2007 3:53 AM
To: [log in to unmask]
Subject: Re: [TN] Aqueous batch cleaner foaming

Technet:

A "proper" defoamer is one which is not soluble in the use solution, but becomes soluble in the rinses... 
This type is known as a polyglycol, and it has this characteristic because it is inversely soluble with temperature, the higher the temperature, the less soluble.   Did I mention that a defoamer needs to be insoluble to function.  Polyglycols are insoluble in warm solution, but in cold rinses, become soluble, thus rinsing easily, thus making the level being used less critical.

Rudy Sedlak

Brian Ellis <[log in to unmask]> wrote: I agree with Rudy, especially about temperature. However, if your first 
water is too hot, depending on the flux chemistry, the cleaning quality 
may be less good. This is especially so if the flux activator contains 
amino acids or their derivatives. The ideal temperature is 55-60°C, no 
higher.

You can buy defoamer from flux manufacturers, but add minimal 
quantities. This is not a case of a little is good, so a lot must be 
better. Alternatively, you can make your own. I quote my book:
"Dissolve 300 g soft white soap in one litre of hot water. When cool, 
add one litre of octyl alcohol. Shake before use. Add the minimum dose 
to obtain the desired effect, usually about 0.1 cm3/l"

Brian

Rob Strecker wrote:
> All,
> 
> Has anyone else had foaming issues in an aqueous wash batch cleaner?
> What are some of the causes of excess foaming?  We are applying our wave
> flux via spray; however this flux is also suitable in foaming flux
> applications.  We are currently in the process of optimizing our flux
> application in the wave to significantly reduce the flux residue on the
> boards.  This includes optimizing the sprayers, preheats and dwell time.
> Initial tests show this is not having a major impact in reducing the
> foaming.  We will be testing boards with only SMT flux residue, then
> ones with only wave flux residue.  The theory is that by themselves they
> do not foam but when mixed cause foaming.  We have recently changed
> Paste suppliers, thus we now have two different manufactures of flux
> mixing in the wash (one from SMT, one from wave).  Could this be a cause
> of excessive foaming?
> 
>  
> 
> Thanks,
> 
> Rob Strecker
> 
> 
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