Benny,
As a bonder, I dont know much about electroplating but I do know
that a lot of places tend to spec a sulfamate layer. I understand this
is because the sulfamate is a more ductile layer, and hence less prone
to cracking during service etc. A couple of important notes, the
plating should be free of organic brighteners and relatively pure Ni
(99%min) and , as these can screw up the initial bondability and also
the long term reliability respectively
Without knowing the exact lay-up the platings, I dont know if you
are bonding onto the Ni iteslf, or a thick layer of soft Au, if onto
Au, the Ni underneath should'nt matter too much, as long as the Au is
well adhered and the Ni doesnt crack.
If going direct onto the Ni itself, I would go for a more ductile,
and softer layer. difficult I know, but try and "match" the hardness
of the Ni to that of the wire, as this will minimise the damage to the
wire during bond, and go for a ductile layer which will withstand the
U/S energy without cracking.
Its difficult to give a green light to either system, I know people
who bond onto both layer types succesfully, with similar machines and
wires.
Having said that, I would be interested in the response from any
plating gurus out there as to the differences between the two layers,
I kinda know what works out on the floor, It would be neat to know why
Regards.
Roger
______________________________ Reply Separator _________________________________
Subject: [TN] Ni Plating for wire bond
Author: "TechNet E-Mail Forum." <[log in to unmask]> at #email
Date: 01/04/99 10:23
Hello Everyone,
What kind of chemistry do you recommend for electrolytic Ni plate, sulfamate
or sulfate nickel, as applied on thermosonic wire-bond PCB? I was told long
time ago that sulfamate nickel is a 'low-stress' nickel being used in
various metal finishing jobs, including PCB; while the latter comes from a
Watt nickel bath. Some BGA designers says that as long as the metal surface
is clean, the two nickel types should work equally well.
I recently tried both and found that the sulfate nickel has a better
bondability, despite the fact that they come from two different vendors.
Can anyone tell me about the surface topography of each type of nickel? Do
they have different atomic packing in the plated layer? What actually does
low/high -stress mean, something related to hardness? Assuming they have the
same amount of gold plated on top, which one is more suitable for gold wire
ball bond?
Thanks in advance!
Regards, Benny.
Wire Bonder Process Eng'g
ASM Assembly Automation
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