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November 2016

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From:
Louis Hart <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Louis Hart <[log in to unmask]>
Date:
Tue, 22 Nov 2016 16:50:53 +0000
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Thanks for all comments on this topic.  TechNet had some discussions on the 'immersion gold' aspect of ENIG maybe 2 years ago. This latest round is even more enlilghtening. Louis Hart



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of George M. Wenger

Sent: Monday, November 21, 2016 5:14 PM

To: [log in to unmask]

Subject: Re: [TN] Immersion Tin - problems



As usual Mr. Hillman gave a really knowledgeable answer and I agree with him totally. I've never pretended to be a chemist or fully understand plating processes but in simple terms what I've been taught to believe that a "True Immersion" plating process is a replacement process where when a metal component such as copper is put into and electrolyte with nobler metal ions, the less noble component or metal will undergo dissolution and this in turn results in the release of electrons, allowing the highly noble metal to settle down. In other words a "True immersion plating process" gabs a copper atom and replaces it with a more noble atom like tin (Sn) or silver (Ag). However, the immersion tin and immersion silver plating processes that are used in final finish plating on PCBs are "basternized" not "True" immersion processes in that they basically grab and replace copper atoms but they also have some "electroless" attributes allowing the plating process to continue increasing the thickness of the nobler metal. 



My original suggestion for a cross section was just to make sure that Jose's PCB shop was giving him PCBs with the proper copper and final plating finish that he specified. If he is getting the proper plating then he needs to control his soldering processes to insure they do not dissolve all of the copper plating. 





----- Original Message -----



From: "David Hillman" <[log in to unmask]>

To: [log in to unmask]

Sent: Monday, November 21, 2016 4:35:07 PM

Subject: Re: [TN] Immersion Tin - problems 



Hi gang - great conversation but I think we need to get ourselves on the same page in terms of definitions. A true immersion plating process is, as Jose and George detailed, self limiting but the majority of the immersion plating processes today would be better described as electroless processes where a reducing agent is a component of the plating formulation which allows the deposition process to continue. Look at the IPC-4556 specification, Appendix 1 (written by Martin Bayes) for a full explanation of the differences between an "immersion" and an "electroless or autocatalytic" plating system. 



Dave Hillman

Rockwell Collins

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