I went through the process of "ruggedizing" both CBGAs and PBGAs about 4
years ago for a former employer.
I'd start by asking for a better definition of "durability".  Are large
shock or vibrational loads a problem, or are you trying to improve thermal
fatigue characteristics?  If the former is the case, I'd go for a very
soft, compliant material to dampen the loads.  There are several potential
candidates out there from some of the major adhesives and epoxy formulators
which could do the trick.  They are generally compatible with normal
assembly and rework operations.

If thermal fatigue improvements are needed, unfortunately you may be forced
to go with the compounds used for flipchip, as has been suggested.   I say
"unfortunately" because I found these compounds to be more expensive (3X),
less process compatible (130C, 6 hour cure), and unreworkable.

After considering these factors, you should look into the processing
required for these materials.  You'll have a choice of premixed/frozen,
multicomponent, or UV curable compounds, at the very least.  Obviously, the
application and available equipment/facilities must be considered.

I haven't revisited the epoxy and adhesive formulators to see if there have
been many new compounds to address BGA underfill within the past couple of
years, but I was told that it just wasn't a large enough application for
them to be concentrating many R&D resources on.  Maybe that's changed, but
I'd doubt it.

Regards,
Greg Bartlett
Teledyne Electronic Technologies
Hudson, NH
[log in to unmask]
--------

try the underfills used in the flipchip industry

> -----Original Message-----
> From: Lage, Bruce [SMTP:[log in to unmask]]
> Sent: Wednesday, August 26, 1998 3:53 PM
> To:   [log in to unmask]
> Subject:      [TN] BGA Underfill
>
> Does anybody have any recommendations and/or experience with adhesive
> underfills to decrease the strain and increase the durability of CBGA
> and PBGA solder joints

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