I just went thru that myself and here are my thoughts.

An ionograph is OK for process control, if you use a high sensitivity
one built for SMT cards.

For process development, I actually removed a BGA and visually inspected
it for flux residues.  You could either use a clean BGA rework station,
or a screwdriver.  Prying the BGA off also gives some insight into the
solder connections. You can see wetting, voids, blowholes, solder dam
conditions, etc. (One could also measure the CCA and the removed BGA in
the ionograph, as a more sensitive test.)

Jim Kittel

>-----Original Message-----
>From:  John Chandler [SMTP:[log in to unmask]]
>Sent:  Sunday, January 24, 1999 11:46 PM
>To:    [log in to unmask]
>Subject:       [TN] BGA clean checking
>
>As you all know. We are getting into doing a basic BGA assembly. The new
>question which came up is, since we run a water soluble flux paste. How are
>we going to know if it is clean under the BGA??  Any suggestions beside
>going to a no clean paste??
>
>Thanks  in advance.
>
>John
>
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