Hi Ioan!
The thickness of 30nm of ImAg is thinner than "normal" by something like a factor of 5! But anyway, you won't be bonding gold to a bunch of ENIG contacts with any decent process repeatability.
The "electrobonded" Au is usually called "electroplated" around here and is the only way to go with gold wirebonding. You want about 600nm of soft wirebondable gold over 3microns Ni. If copper gets into the metal mixing for gold bonding, you are doomed. So the copper is just a base metal which is kind of soft and insulates you mechanically from the substrate. Not a good thing. Also, of course, it limits the conductor resolution and edge quality.
2 mil wide traces!!!? And they are 25 microns thick? That is a wonderful aspect ratio to image/etch at all! But it will be quite difficult to bond gold to because the elevated temperature required for gold bonding will soften the bond between the copper and the dielectric--the pad will wiggle alot during application of the ultrasonic scrub.
As Inge says, bonding with Al to ENIG is not a problem, and that is room temperature. But Al is much more difficult to target on small stuff because it is much stiffer than gold and the wedge bonding process isn't quite as accurate as ball bonding. I've bonded to Al to bare Cu, as long as its very clean, so even ENIG isn't absolutely necessary.
Wayne Thayer
________________________________
From: TechNet on behalf of Hfjord
Sent: Fri 3/7/2008 11:36 AM
To: [log in to unmask]
Subject: [TN] SV: [TN] Bonding on ENIG
Ioan,
We have been bonding with heavywire Al wire to ENIG type a) hundreds of
thousands boards, works perfectly.
Au ball/wedge fine wire won't work with 6S confidence on any of a) or b)
because the gold is too thin.
http://www.empf.org/empfasis/2007/June07/wedge.html
Inge
-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Ioan Tempea
Skickat: den 7 mars 2008 14:06
Till: [log in to unmask]
Ämne: [TN] Bonding on ENIG
Hi Technos,
A connector has to be bonded on 2 mil wide traces. Is ENIG suited as a
surface finish for bonding? If yes, why, if not, why and if it depends, why?
Or otherwise said, I have a PCB that will get some SMT parts on both sides
and then a couple hundred golden fingers will see bonding. I was presented
with 2 options for the PCB finish:
a) Immersion Gold : 0.03um Au over 3um Ni over 25±10um Cu
b) ElectroBonding Gold: 0.3um Au over 3um Ni over 25±10um Cu
Which one is to prefer?
Thank you,
Ioan
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