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December 2006

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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 14 Dec 2006 13:21:16 -0600
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Hello Bev - see my comments below:

Dave Hillman
Rockwell Collins
[log in to unmask]




             Bev Christian
             <[log in to unmask]
             OM>                                                        To
             Sent by: TechNet          [log in to unmask]
             <[log in to unmask]>                                          cc

                                                                   Subject
             12/14/2006 12:50          [TN] Qualifying reworkable
             PM                        underfills


             Please respond to
              TechNet E-Mail
                   Forum
             <[log in to unmask]>
             ; Please respond
                    to
               Bev Christian
             <[log in to unmask]
                    OM>






Technetters,
Back after almost a year off-line.

*** Welcome back

It has always been my philosophy to thoroughly test ANY chemical that is
going to come in contact with a PCB or PCBA - tapes, labels, inks,
markers, adhesives, cleaners, temp solder masks, permanent solder masks,
flux stops, lubricants for compression fit pins, solder wicks, dusters,
freezing agents, OSPs, cored wires, fluxes, thinners, tacky fluxes,
paste fluxes, solder pastes, underfills, conformal coatings and thermal
compounds.

*** Good philosophy and are you sure that your list is complete? : -)

Lab testing includes copper mirror, halide ion, SIR and electrochemical
migration.  It sometimes includes other tests, but let's leave it at
this for the moment.

*** Wait a second - you didn't mention Ion Chromatography! You are going to
make Mr. Pauls feel left out.

Here's my problem: I have tested many reworkable underfills from all the
people you can think of and I CAN'T FIND A SINGLE ONE THAT WILL PASS
BOTH IPC SIR AND ECM TESTING.  These materials were tested at the same
time that we had control coupons in the chamber (passed), solder pastes
(passed) and normal underfills (passed), so I doubt it was the chambers
(more than one) or that there were water droplets (checked, none
evident).

*** Ok , here is the only serious comment of the reply. Something doesn't
make sense. The underfill materials surely meet the IPC SIR/ECM
requirements in a standard material test otherwise the suppliers would not
market the underfill materials. So, my guess would be that possible root
cause for your reworkable underfill failures would either be improper
curing of the material (uncured underfill will not pass SIR/ECM) or there
is a reworkable underfill/solderpaste flux incompatibility issue. Those
are the two items I would chase. Have you conducted IC testing on the
SIR/ECM coupons to see what extractable species are present?

My customers are pushing me to allow them to use the stuff and I am
resisting.  Comments, please.

*** You have three options:
-Resistance is futile, you will be assimilated.....
-Walk away from the light............
-Have the Technet crew give you suggestions

Bev Christian
RIM

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