I agree that a full validation would be prudent. Otherwise how would one
know that the failure wasn't due to an intermittent in the component or
board and that the addition of flux and the subsequent heating just lead to
a temporary closing of the intermittent?
Regards,
Bev
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Wednesday, November 14, 2012 8:27 AM
To: [log in to unmask]
Subject: Re: [TN] Reflux and reflow BGA rework
Scott, are you working on field repair or production repair (yield fall
out)? If it is later.. wow.
Joyce Koo
Materials Researcher - Materials Interconnect Lab
Research In Motion Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Post, Scott E
Sent: Wednesday, November 14, 2012 7:12 AM
To: [log in to unmask]
Subject: Re: [TN] Reflux and reflow BGA rework
In your example of field failures after "fixing" a BGA with flux and reflow,
was the repair for HIP? If so, what was the failure mode? I've been asked
about doing this to repair HIP a few times over the years and I've always
erred on the side of caution and said no since I didn't know if or how we'd
get bit. It'll eventually come up again and I'd like to have a better story
than, "it makes me uncomfortable". I think next time it comes up I'm going
to suggest repairing some and putting them through a full validation cycle
so we have some data. The problem is that the question always comes up in
the heat of a crisis.
Thanks.
Scott Post
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana 46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Tuesday, November 13, 2012 10:28 PM
To: [log in to unmask]
Subject: Re: [TN] Reflux and reflow BGA rework
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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