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July 2011

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TechNet E-Mail Forum <[log in to unmask]>, Russ <[log in to unmask]>
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Tue, 5 Jul 2011 10:14:43 -0500
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Hello TechNetters,

I have a question about acceptable BGA repair methods.  I have always required my EMS's to pre-apply solder paste to either the PWB or device prior to placing and reflowing a BGA.  Some of my EMS's pushed back initially but always complied.  IPC-7711/21B has two defined repair methods which both require adding solder by either pre-applying solder by using solder wire (section 5.7.1) or using solder paste (Section 5.7.2).  No where does IPC-7711/21B state that you can get by with only applying tacky flux.  Here is where I feel there is a conflict.  In IPC-7095B Section 6.1.2 it states a couple places that you must "new solder paste or flux".  No where does it mention pre-applying wire solder before applying the flux.  IPC may want to review the wording there.

I am not sure how you would control manually applying core (wire) solder so I only consider pre-applying solder paste an acceptable method.  I am a firm believer that by not applying solder paste reduces the solder volume, joint height and thereby reducing reliability of the solder joint.  

First, I would like to know if anyone knows of a published reliability study of Flux only versus Pre-pasting a BGA repair.

Second, I would like to hear other opinions on this subject.

From a processing standpoint I understand the EMS's position that applying tacky flux makes the BGA repair a whole lot easier and cheaper as adding paste requires a mini-stencil and a trained operator.  I am all for easy if it does not but reliability at risk.  I also have a concern about the excessive flux that I find under a BGA that has been attached with only tacky flux.  They are no-clean fluxes but but excess is never good or pretty.  Thanks in advance.

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