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January 2012

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Subject:
From:
Steven Creswick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steven Creswick <[log in to unmask]>
Date:
Tue, 17 Jan 2012 12:47:55 -0500
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Sayed,

We can read you!!!  What did you change?  Can you tell us?


Just a few quite generic suggestions...

First question I would ask yourself is whether you wish to be able to rework
the device or not.

Next would be method of application.  Pre-applied [no-flow/flux underfill],
or post applied [capillary flow].  The pre-applied is sexy.  Comes out of
reflow and its done!  Can have problems, but so can the capillary underfill
approach.

Third question would be whether you had any cure time/temp limitations [if
you go post-applied].


You have a very low I/O count.  What is the approx ball size?

You can go to any of the large adhesive manufactures for assistance and some
of the solder paste manufacturers as well.  Ones that quickly come to mind
are Henkel [which is a combination of Loctite, Ablestik, Emerson & Cuming,
et. al.], Cookson...

You don't provide enough info on the other conditions, substrate,
constraints, reliability requirements etc. to really be able to provide a
slick answer.  In general, however, I am always cautious of the high CTE of
neat silicones [generally in the 200-300PPM  range].  Yes, it will be
heavily filled to modify the CTE, but do you gain anything on the cured
system?  Silicones also tend to be more expensive than semi-generic epoxy
based systems.  Just do your homework...

I suggest you stay with the available epoxy based systems as a simpler,
easier solution unless your device, substrate, or requirements are out of
the ordinary.

Steve Creswick
http://www.linkedin.com/in/stevencreswick




Depending upon the other conditions of your project
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ahmad, Syed
Sent: Tuesday, January 17, 2012 12:20 PM
To: [log in to unmask]
Subject: [TN] silicone-based underfill. Resending in plain text

While trying to gather info on possible options for an underfill for an
approximately 2 x 2 mm chip with about a dozen solder balls, we came across
a silicon-based underfill online. Any experience or info about its use in an
RF system? A good source for it if it is a viable option?
Thanks.
Syed Sajid Ahmad
Center for Nanoscale Science and Engineering (CNSE)
NORTH DAKOTA STATE UNIVERSITY
www.ndsu.edu/cnse




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