I would have to disagree.  We have successfully cleaned under ~1" * 1"
leadless chip carriers (which only have about a 0.002-0.005" clearance)
and verified cleanliness using both visual and SIR measurements (in a
condensing humditiy test).  We did work also with QFPs and found (by
comparitive SIR measurements on the same PWAs) that the QFPs were EASIER
to clean under than the LCCs and our initial evaluations indicate BGAs
are easier still (due to the relatively large spacings; on the order of
0.010 mils (PBGA).

===============================
Jim Maguire
Senior Principal Engineer
Boeing Defense & Space Group
(206)657-9063     fax 657-8903
Email:  [log in to unmask]
================================

>----------
>From: 	[log in to unmask][SMTP:[log in to unmask]]
>Sent: 	Friday, March 07, 1997 5:12 AM
>To: 	[log in to unmask]
>Subject: 	Re: Cleaning of BGA
>
>Hi Poh
>
>In my opinion there is no way to clean the solder joints underneath a BGA.
>You might even worsen the situation because the polymer matrix of the flux
>residues close to the edge of the BGA will be cracked in a cleaning agent.
>This solution is washed underneath your BGA and will contaminate the inner
>row of balls even worse than they where before. Additionally, if you have
>tracks underneath your BGA, the SIR between the tracks will be affected
>with all the rubbish you wash under the component. We made trials with
>QFP's, where we saw that residues are washed underneath the component but
>that the rinsing operations where not able to remove the sauce accumulating
>underneath the package.
>
>Best regards
>
>Guenter Grossmann
>
>
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