Ingemar,
Yes - matching material hardnesses [plating to plating and wire to plating] all makes sense.
Down deep inside do you feel the fundamental PRIMARY issue with ball bonding onto ENIG is the hardness of the nickel beneath?
If we could get a pure [lack of grain refiners & brighteners] electroless nickel do you think it would work? This would seem to put us back to the old standby of a relatively soft electrolytic Ni-sulfamate bath - aka electroplated Ni-Au don't you think.
This is all very interesting.
At the moment, I need a PWB with both wire bondable [gold ball] and solderable surfaces for a COB application. As you might guess we are having problems with our current electroless Ni/Pd/Au. Am even looking into Rudy Sedlack's immersion Pd
Will keep you posted, however, am also interested in your comments as a suitable/repeatable/reliable ENIG for gold ball bonding would be a godsend to many of us. Am going to see if I can spend some time digging into the electroless Ni process a bit and see if there is something out there that can provide us with the soft Ni. Any guidance would be appreciated.
We are beginning our Fall season over here. Will have to bring some pics in and compare notes on tree coloration. Took some very nice ones last Sunday. Has been a dry summer, so colors are very muted in most spots. Although some are very nice. Even have my wife flying with me now although she does not "get into it" as much as I do. She still basically likes to have her feet planted firmly on the ground, if given the choice. :-)
Steve
-----Original Message-----
From: Ingemar Hernefjord [mailto:[log in to unmask]]
Sent: Wednesday, October 19, 2005 4:36 AM
To: [log in to unmask]
Subject: [TN] SV: [TN] SV: wire bondable immersion gold
Joe,
Like many others, we have been experimenting with gold ball bonding on
nickel with a thin gold plate. With 6 sigma in mind, we were not
satisfied with the results. Reason seemed to be that there was a bad
match between the sof gold (HV~80) and the very surface of nickel
(HV~300). Tests on matte nickel performed well, but the board maker
could not plate matte nickel at that time. We tried doped gold wire with
various hardness, and got better results, but still not obtaining zero
bond failures we abandoned the project. Wedge gold wire bonding,
however, is different. We have made some products with this method on
0.05 um gold over nickel, and with good results.
Ingemar
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Joe Fjelstad
Skickat: den 18 oktober 2005 22:58
Till: [log in to unmask]
Ämne: Re: [TN] SV: wire bondable immersion gold
Hello Inge and Joyce,
You are right, Inge, that folks have been using very thin gold for
aluminum
wedge bonding for many years (and have even in some cases bonding
directly to
nickel as you mention).
The importance of thin gold with aluminum wire (and conversly thin
aluminum
with gold wire) is a hard won lesson left over from the days of the
"Purple
plague".
However, there actually is a link within the link that shows images of
ball
bonds not wedge bonds.
There is no process detail but the text reads (company name removed):
"Wire-bond process for high-temperature applications produces bonds that
are
stable at high temperatures with a thinner gold layer. These special
high-temperature wire bonds are especially useful in avionics and
automotive apps, and
require no additional lead time for production. The wire bond process
eliminates the Kirkendall voiding that takes place in an Al / Au
interface at 200°C
thermal exposures."
It is obvious from the wording that they have concerns of Kirkendall
voiding
and they are finding benefit in not making the bond directly to
aluminum. Even
so that is mighty thin gold for gold ball bonding to be sure. It is
impressive if they are pulling it off repeatedly.
Kind regards,
Joe
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