To add to this, most rework persons add more flux as a means to ensure the flux spreads out and wets the entire BGA during reflow. I have seen that this is a strategy not without pitfalls as you end up with pools of flux that still do not spread, especially for larger BGAs and you end up with conditions not unlike what was described in the original thread. That is why I do not like to perform a "reflow only" operation. 

As an aside, Dave, is there a method to determine how much flux has spread underneath the component during a reflow only operation?

Thanks,
Amol
    

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, November 13, 2012 6:22 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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