Gold bonding requires electroplated gold. Either the electroplating will be done with "buss bars" or the outer layers will be pattern plated with gold.
If pattern plating, the gold stays there, and you will have under-cutting of the pads which will be at least as much as the thickness of the copper under the gold. Not many fabs know how to check that, so most stuff comes out way over-etched (but that nice gold on the surface looks great--until it falls off!).
Aluminum bonds to copper just fine, so this isn't an issue. Even ImAg works pretty well to protect the copper from oxidation. But wedge bonding has its own issues--decreased speed, more brittle wires, more difficult looping, etc.)
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
Sent: Tuesday, August 04, 2009 1:02 PM
To: [log in to unmask]
Subject: Re: [TN] Wire bond
Hi Joyce,
Do not understand your response - why would a .002 etched pad be flatter in
the centre - I have done thousands of x-sections and SEMS - never seen this.
Why would I have exposed copper at an edge- never built a wire bond circuit
that would have that issue. Regards Steve
Steve Kelly
PFC Flexible Circuits Limited
PH: (416) 750-8433
Fax: (416) 750-0016
Cell: (416) 577-8433
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, August 04, 2009 12:56 PM
To: [log in to unmask]
Subject: Re: [TN] Wire bond
Yap. The flatness of the center pads is better than the edge, just in case
you have some exposed copper at the edge, that will harden the gold locally.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Aug 04 11:36:30 2009
Subject: [TN] Wire bond
Good Morning,
Does the size of a wire bond pad (in this case with a perfect etch .002
wide) have any effect on whether the wire bonder does Al wedge or
Thermosonic gold( I know the gold plating is different) - just asking about
the process. Thanks. Steve Kelly
Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)
(416) 750-8433 (work)
(416) 750-0016 (fax)
(416) 577-8433 (cell)
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