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November 2012

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From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 14 Nov 2012 09:28:13 -0600
Content-Type:
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Hi George -  good discussion and I completely agree. I should have been 
more detailed in my response. We do not use the "reflux and reflow" 
process as a routine procedure. As you detailed, we do a root cause 
investigation and do not allow the process to be used without some due 
diligence. And as Richard detailed in his response, our "reflux and 
reflow" process is a detailed process with specific procedure steps that 
must be used. Use of the "reflux and reflow" process without conscious 
thought can get you into trouble as you suggested. A good example was one 
case where we found that a lot of boards had crack microvias in the BGA 
pads so when the BGA was reflowed, the solder electrically  "reconnected" 
the microvia giving the impression that there was a bad solder joint when 
in fact there was a bad microvia fabrication process.  I agree with you - 
blindly using a "reflux and reflow" process can be dangerous practice.

Dave



From:   "Wenger, George M." <[log in to unmask]>
To:     <[log in to unmask]>
Date:   11/13/2012 09:30 PM
Subject:        Re: [TN] Reflux and reflow BGA rework
Sent by:        TechNet <[log in to unmask]>



Julie / Dave,

I'm going to stick my neck out and say that injecting flux and 
re-reflowing is a risky repair process.  You may be able to make a part 
that wasn't working work again but just because it works again doesn't 
mean you have reliable solder interconnections.  I'm aware of a case were 
injecting flux and re-reflowing did fix PCBA product well enough to pass 
functional test and those "fixed" boards failed after being deployed.  The 
problem with "fixing" non-working BGAs is that the non-working BGAs may 
have been "fixed" but you don't know what was "fixed" and you don't know 
how good the "fix" is.

Before fixing any non-working BGAs I think the important thing to do first 
is identify what you are trying to fix.  Is the BGA non-working because of 
Head-n-Pillow, Double Reflow, Insufficient solder paste dispensing, 
Plugged stencil aperture and no dispensed solder paste, Poor wetting, 
De-wetting, etc.

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, November 13, 2012 9:22 AM
To: [log in to unmask]
Subject: Re: [TN] Reflux and reflow BGA rework

Hi Julie - I don't know of any standards that cover this topic unless 
there is something in the IPC-7711 specification. When we use our BGA 
repair procedure, we use specific fluxes that are easily removed and we 
are very conscious about the volume of flux used. "Bigger the glob, better 
the job" is not a applicable process philosophy when utilizing fluxes for 
BGA repair. Our focus for the process is to insure that we are using flux 
in such a way that we don't cause a reliability issue that was not there 
prior to our BGA repair actions. The example we discussed of the flux 
packed under the BGA in the previous Technet thread is a classic case of 
not understanding how much flux was necessary for successful BGA repair.

Dave Hillman
Rockwell Collins
[log in to unmask]



From:   Julie Silk <[log in to unmask]>
To:     <[log in to unmask]>
Date:   11/13/2012 07:51 AM
Subject:        [TN] Reflux and reflow BGA rework
Sent by:        TechNet <[log in to unmask]>



A discussion of the practice of re-flux and reflow of BGAs to rework them 
has emerged within the "limits of flux residue" discussion.  I'm taking it 
out into a separate thread.  This rework process injects flux under the 
BGA, then reflows the BGA.  The part is not removed.  It will frequently 
make a part that wasn't working work again.  The heat damage to the board 
is less (fewer cycles) than a replacement process.  The question Joyce 
asked about whether there are standards and reliability studies has not 
been answered.  What is the proper procedure for this rework process?  Are 
there official standards?  Studies of effectiveness / reliability?




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