You will want to use solder paste.  Theoretically you do not have to
because the PBGA balls are Eutectic, however, when I set up the BGA rework
process I tried to rework them with just flux with little success.  We
purchased the top of the line Airvac rework station, but the inconsistency
in the balls collapsing will cause some of them to pull up tighter to the
package then others and thus never touch the pad.

We purchased a small stencil that I attached to the nozzle of the Airvac,
aligned the stencil using the vision system on the Airvac and screened
paste on the pads.  With this process you can make up for the inconsistency
and be assured every ball will solder.  I do not remember where we got the
stencil from as I set up this process a couple years ago at my former
company.  OK Industries used to market the machine and stencils for a
company in California.  Call them or a rep. to get more information.  I did
not purchase the machine as it was about 1K.  You can purchase the stencils
that go on that machine and make up a fixture using one of the hot air
nozzles on the Airvac and actually use the vision system on the Airvac to
align the stencil before printing it.  This process is really slick and
works well (and I saved 1K).

Basically, you can rework them with just flux, but if you want to be sure
to have complete soldering of all the joints, use paste.

Brad Kendall
Hella Electronics Corp.






[log in to unmask] on 02/11/98 09:03:04 AM

Please respond to [log in to unmask]; Please respond to [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: Brad Kendall/Hella North America Inc.)
Subject:




We currently use solder paste when we do rework on PBGA's.

I?m interested in knowing if it is required.  I heard that the paste was
not required for PBGA's, only for CBGA's.  Is that true ?  If so, do we
only have to put flux on the board to be rework before putting the new PBGA
?

Thank in advance.

------------------------------------------------
Stephane Richard
Ingenieur de procedes
Process Engineer
Matrox Electronic Systems Ltd
E-mail: [log in to unmask]
Telephone:(514)969-6000 ext.7585
Pagette : (514)201-0044
Fax:      (514)685-3415
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