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April 2008

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Subject:
From:
Kevin Glidden <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kevin Glidden <[log in to unmask]>
Date:
Fri, 11 Apr 2008 11:39:13 -0400
Content-Type:
text/plain
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text/plain (161 lines)
Very true.  This is a well known problem.

Bellcore/Telcorida did not allow use of water soluble flux after rosin based
solder.  They were worried that some of the water soluble flux could be
trapped in the compliant rosin flux residue left form the topside assembly
and wouldn't be completely removed during a cleaning process and could
therefore be released during the life of the product if the rosin softened
during a use temperature increase.

To quote advice given once from Doug Pauls right here on Technet:
mixing flux Bad Idea Kimosabe!

I have seen this failure first hand.  We buy a transformer for use in power
supplies.  The supplier soldered using a no-clean and did not remove the
residues. We were soldering the transformer in with water soluble.  We
received returns from field with a fire on the pcb. It burned out a trace
through the PCB under the power pin of the transformer.  We now have the
supplier clean the transformer.

Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.

-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]] 
Sent: Friday, April 11, 2008 11:13 AM
To: [log in to unmask]
Subject: Re: [TN] Possible flux contamination issue

Yes, and conductive, resulting in the shorting issues. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Joseph E (US
SSA)
Sent: Friday, April 11, 2008 10:11 AM
To: [log in to unmask]
Subject: Re: [TN] Possible flux contamination issue

I can see how no-clean residue on the part could soften during reflow,
allowing highly active ionics from the water soluble flux to mix in and
become entrapped in the rosin (or resin, or whatever) matrix.  The
result would be a a highly active residue that could be very tough to
clean.

-Joe


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Friday, April 11, 2008 10:15 AM
To: [log in to unmask]
Subject: Re: [TN] Possible flux contamination issue

A quick answer is that mixing flux types is generally a no-no! You have
no idea what the reactions may be between the two fluxes.

Brian

Steve Kelly wrote:
> Good Morning,
> 
> We are assembling a BGA connector onto a flex circuit. The BGA has 
> leaded balls and the BGA manufacturer uses a no-clean process to 
> attach the balls to the connector and does not clean afterwards.
> 
> When we assemble the BGA connector to the flex we use water soluble 
> paste and then we clean. After damp heat cycling we have seen some 
> shorts. When we take off the connector we see flux residues on the 
> underside of the connector but not on the flex.  So my question is - 
> what are the concerns about mixing no-clean and water soluble? Is the 
> failure likely due to inadequate cleaning or is there something else I
should be concerned about.
> I realize this is probably not the way it should be done but some days

> you just do what the customer wants - good or bad. Thanks in advance. 
> Steve Kelly
> 
>  
> 
> Steve Kelly
> 
> (416) 750-8433 (work)
> 
> (416) 750-0016 (fax)
> 
> (416) 577-8433 (cell)
> 
>  
> 
> 
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