Tim Mendenhall asked:

>     We are currently establishing our BGA process and have several
>     questions:
>
>     1. What is an acceptable amount of times a BGA device can be
>        reworked, reballed, and remounted?

Zero (for PBGA's) - you get one shot.

I suppose you may want to disprove the above. Go for it - see
http://www.smtnet.com/smt_forum/messages/59.html for a suggestion. I guess
there is a company Winslow Engineering in Sanata Clara, CA who has
something called BGA "SolderQuik" 408-496-6636. Their trick is a paper
carier for a matrix of solder balls. The paper carrier (with solder balls)
is placed on the clean, fluxed underside surface of the BGA and reflowed.
After reflow, the carrier is softened with water and peeled off, leaving a
matrix of reflowed solder spheres on the BGA. Doug Peck says it works well.

My comments based on the fact that Motorola told me they would not reball
any PBGA parts for us, and that they considered it NR. We have not tried
the above. Seems to me that you are talking about 3-4 reflows and a lot of
labor, high risk of part/PWB damage. Let me know how you make out.


>     2. What are the critical elements to consider and why?

design of the pads at board layout
moisture sensitivity of the part (pkg and handling prior to assembly).
reflow profile - (low peak temp), tight delta T.
good rework equipment/process with profile capability


>     3. What is the maximum number or percentage of solder voids allowed
>        per solder joint (bump) connection?

depends on void size - some are inevitable, I have heard max dia 1/4
collapsed ball dia as a guideline.

>     4. Has IPC released a BGA standard?

sorry, don't know, but I would guess it is out or in work. Good excuse for
more committee meeting in Florida.


cheers,

Jerry Cupples
Interphase Corporation
Dallas, TX USA


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