Don,
You say they verify cleanliness of the board after cleaning. They
should, but what I think you meant was they verified cleanliness after
the assembly process.
Normal acceptance values of 1.56 or 10 may not be adequate. You did not
mention the pitch of the BGA (I deserve credit here for not asking the
question the way I wanted). Some 1 mm and .8 mm flash memory BGAs
require cleanliness levels that are beyond the ability of an Omega meter
to determine.
The bare PWB/PCB/board, whatever term you like, should be down in the 1
to 2(.3 to .4)range. SIR and Ion Chromatography need to be done as an
initial Qual and as a verifier that the process, once established is
still in control. The BGA packages themselves are often not clean enough
in their as received condition to ever realize an acceptable level of
cleanliness at final assembly. 
These requirements are based on needing long term life for a high rel
product used in a humid environment with small dc bias voltages and your
Integrated Supply Chain people making all the technical decisions on who
builds the product.
Dewey   

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Donald Vischulis
Sent: Thursday, March 09, 2006 3:59 PM
To: [log in to unmask]
Subject: [TN] Cleaning Qualification Question

All

I've been assigned the task of determining if a supplier's current
cleaning process is robust or if additional testing is required to be
able to say that the product is clean enough to provide years of field
use.  The board is a 2-sided Class 3 assembly (95% SMT) with one BGA and
about 1500 other components. The assembly is soldered with a water
soluble flux, it's cleaned in a batch cleaner with DI water, and is
conformal coated.  The current manufacturer is using and Omega meter to
verify the cleanliness of the board after cleaning.

My questions:

Is this process good enough to provide a reliable product in an aircraft
application?
If not what guidance is available to determine what level of process
qualification is needed to answer question #1?

Any help is really appreciated.

Don Vischulis

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