Steve,
If I had my choice, I prefer a good electrolytic NiP plate, however, reality being what it is, one freqently has to deal with the need for electroless.
As long as the nickel plate is uniform, pore free, and of sufficient thickness, both seem to work well. The question becomes one of how much nickel thickness is required to prevent the underlying substrate material [copper?] from diffusing through the nickel as a consequence of the environmental conditions [elevated temperatures] which you expose the product to prior to wire bonding. I like 150-250 µinches in many cases, but there is nothing saying you may not live with say 50-100, or some other intermediate range. I would caution about going too much thicker than 250-350. Just be sure to give the plater enough of a range to make his life easier, hence your supply chain easier and costs lower.
I have used this basic approach for both aluminum [fine and heavy wire] as well as gold wire bonding. In the case of the aluminum wire, we are bonding through the gold [keep it thin] to the nickel. In the case of gold wire bonding, we are bonding to the gold [keep it thick and pure] :-)
Now then, I am not sure how the other members of the forum feel [gold wire bonding - and please do not feel that I am knocking any of the very knowledgeable and tremendously good plating folks out there], but I have yet to be able to set up a process with the electroless golds and have the consistency, repeatability and quality of a good ol' fashioned, clean, pure, soft, electrolytic gold. My Weibull plots with a good electolytic gold are super tight, consistent, and don't have the unsettling out-lyers to contend with - only the cost.... Product quality vs cost .... hmmm
Like Joyce indicates, if you are gold wire bonding ... definitely not all golds are wire bondable. This may sound very negative for a Thursday, but if someone has a good, consistent, electroless nickel - electroless gold supplier and they do not mind sharing the name, I am all ears ...
You might also look into the Ni/Pd/Au approach. There seem to be some pros and cons. From a practical standpoint I still see far too much variation to make me comfortable. I want nearly perfect - all the time - with each lot, and usually I am willing to pay for it.
Steve Creswick - Gentex
-----Original Message-----
From: Steve Kelly [mailto:[log in to unmask]]
Sent: Thursday, August 25, 2005 9:31 AM
To: [log in to unmask]
Subject: [TN] Wire bondable gold
Good day to all,
Does it make any difference if the nickel underneath the wire bondable gold
is electroplated or electroless? Thanks in advance. Steve Kelly
PFC Flexible Circuits Limited
Ph: (416) 750-8433
Fax: (416) 750-0016
Cell: (416) 577-8433
E-Mail: [log in to unmask]
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