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November 2012

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From:
"Post, Scott E" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Post, Scott E
Date:
Wed, 14 Nov 2012 12:11:40 +0000
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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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