Subject: | |
From: | |
Reply To: | |
Date: | Wed, 14 Nov 2012 09:28:13 -0600 |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
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?
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
|
|
|