David,
I
can not say that I have bonded to immersion silver (yet), but have begun to
consider it.
Getting down to only 6 microinches sounds a
little questionable - especially if the boards have experienced reflow,
and have possibly sat around prior to die attach (another bake/cure) and
wire bonding. Are you sure you are getting 6 microinches?? At 6,
you might just as well ask for a "flash" and keep your fingers and toes
crossed that everything will work - and that you did not get 2, 3 ,
maybe 4 microinches instead.
With
thin gold, I would expect to see lifted wedges at the bonder (no sticks), and
low second bond pull strengths at wire pull. I would expect virgin
boards to give better results than those boards subjected to any
elevated temperatures and/or staging times prior to wire bonding.
I begin to get really nervous if my 1
mil wires began to have bond failures at <6-9 grams
(depending upon the tensile strength of the wire). Wire
breaks I can sleep with, but the bond lifts scare
me!
Lastly, you have not indicated whether this is the
"first time" you have bonded to these boards (and may still be seeking the
optimium bond schedule and capillary face style/angle), or you have been
running them all along, and just now have begun to have a
problem.
Is
your laminate capable of handling the temperature at which you are
bonding?
The
"fifth degree", not intended. :-)
Steven Creswick
Gentex Corporation - A Smarter
Vision
Hi,
Can anyone share his experience on gold ball
bonding on COB with immersion silver finishings. What sort of silver
thickness to ensure a good bonding strength of min 3.5 gf?
We are using a 1 mil thick gold wire on a 6 to
20 microinch silver thickness and encountered difficulty in achieving the
min bonding strength in wire pull.
Thanks for all inputs.
Best regards,
David.
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