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November 2012

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Subject:
From:
Reuven Rokah <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Reuven Rokah <[log in to unmask]>
Date:
Wed, 14 Nov 2012 14:23:18 +0200
Content-Type:
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text/plain (155 lines)
Agree,
Check the reason of the BGAs failure, if it happened once, it will occur
again without corrective actions.
Reuven

On Wed, Nov 14, 2012 at 2:11 PM, Post, Scott E <[log in to unmask]>wrote:

> 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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-- 

Best Regards,

*Reuven Rokah*

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