That's very true- initially we baselined the amount and porosity of the
underfill of the same BGA soldered onto a PCB and "soldered" onto a
glass slide. This was done by microsectioning- didn't have access to
acoustic microscopy but that sounds like a good idea. 

 


Tom

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, November 01, 2007 7:06 PM
To: [log in to unmask]
Subject: Re: [TN] verifying BGA underfill coverage

Hi gang! Just one additional comment to add to Steve's good information.

The wetting characteristics of glass are not the same as most BGA
laminate materials so after using dummy glass methodology that Steve
described, it is always a good idea to run a few samples with the
specific BGA to confirm that you are getting the flow distribution that
you expect.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Creswick, Steven" <[log in to unmask]> Sent by: TechNet
<[log in to unmask]>
11/01/2007 05:07 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Creswick,
Steven" <[log in to unmask]>


To
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cc

Subject
Re: [TN] verifying BGA underfill coverage






Joe,

Acoustic microscopy is about the best method I can think of, but you
still need to be an intelligent consumer.  The biggies like Sonix and
Sonoscan both make good equipment.  The transducers and software really
make the difference, and the software is improving on a continuing
basis.

It is also possible to make 'dummy' flip chips if you have access to
metal deposition and patterning of glass.  Buying and placing solder
spheres is the only other task that you would need for that approach.
It REALLY helps to understand the under-fill's flow characteristics when
you can actually see it as it happens.  I learned a great deal from this
approach using an old Camelot 1414.

Ever considered a flux under-fill [or no-flow under-fill]?

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Macko
Sent: Wednesday, October 31, 2007 7:34 PM
To: [log in to unmask]
Subject: [TN] verifying BGA underfill coverage

Fellow Techs

 

We purchased a GPD automated epoxy dispenser and I want to proof out the
new automated underfill application process on BGAs. We use a wickable
Loctite underfill that requires an elevated temperature to flow properly
under BGAs, etc..  Currently we successfully underfill by hand and want
to switch to an automated process using the GPD. 

 

I want to verify the underfill coverage under BGAs using a
non-destructive test method. The only non-destructive method I am aware
of is acoustic imaging using an instrument such as Sonoscan, which I
believe will show voids in the underfill material. I do not know how
industry non-destructively verifies underfill coverage.  I plan on
physically removing some BGAs on scrap boards to verify coverage but do
not want to do this on good boards for obvious reasons.

 

Question - What is the commonly accepted non-destructive method for
verifying BGA underfill coverage?  Look forward to your comment. thanks

 

Best Regards,

- Joe

 


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