Blair,
   I have run hundreds of assemblies through Ionic testing.
1. I have discovered failures for no apparent reason and it turned out
to be the PCB's themselves. Now I have the PCB's tested when they are
fabricated (at the board shop) and have no more IONIC contamination
failures do to contamination at all.
2. Even though 100% of our boards are being tested for IONIC
contamination we have had a few boards hear and there that have failed
electrical testing because of flux entrapment under BGA's that are
around 1MM pitch.  After removing the BGA it looks like a dark
gray\black blob of corrosion probably do to the power going through the
resistance of the flux and solder.
My suspicion is that the water molecules don't always make it under
BGA's to remove all of the flux from processing.  Interesting though I
don't seem to have had problems with micro-BGA's.
One other point is that we use water soluble flux as a process and not
no-clean fluxes because of the appearance of our products.

Hope this helps,
Pete Siperek, IPC(CID+) 
Sr. Staff Engineer 
Delphi Engineering Group, Inc 
phn 949-515-1490 ext. 478 
fax 949-515-1491 
[log in to unmask] 

Your Partner in Product Development 


 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: Friday, October 30, 2009 6:40 AM
To: [log in to unmask]
Subject: [TN] Cleanliness

A ROSE by any other name would smell as sweet, right SIR?

Happy Friday, Technetters! As you may have guessed, I've spent a bit of
time over the last few days looking over cleanliness testing specs,
searching through the archives and what not to get more information on
the different types of testing. Now it is time to visit the well of
knowledge and see if the Technet gurus can help me along the road to
cleanliness enlightenment.

From what I understand, the ROSE test measure the change in resisitivity
/ conductivity of a test solvent solution (75% IPA / 25% DI Water) that
is rinsed over a board / assembly. This will detect contaminants and
provide a relative level of the contamination. However, it will only
detect those contaminants that are ionic in nature or will affect the
resistivity (is that redundant?). The results are near immediate.

The SIR test measures the insulation resisitance change that occurs when
an assembly is exposed to humidity and voltage, and thus has the
capability of detcting the presence of contaminants that may not be
ionic, but can cause corrision and / or dendrites to grow. The drawback
is that the samples must be exposed to controlled humidity / temperature
for a priod of time. 

Does that sound right? Am I missing anything? 

Are there any other options?

Thanks,

Blair

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