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April 2005

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Subject:
From:
George Carroll <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, George Carroll <[log in to unmask]>
Date:
Wed, 20 Apr 2005 11:49:52 -0400
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Gentlemen,

Perhaps you can settle a question that has been in my head for several years regarding black pad:  Because ENIG is a redox reaction and many of the areas being immersion gold plated are connected together electrically on the board, might this give rise to electron rich and poor areas similar to the hich current density areas I experienced in electroplating?  Would this, in turn, cause more rapid or retarded gold deposition in certain areas?  Picture a fairly large exposed surface area connected to an isolated contact or finger.  Would it drain electrons from ( or supply excess to) the isolated feature tend to promote the appearance of black pad in that isolated area especially if the phosphorous content of the nickel or the chemical balance of the gold bath were a little off.  As I recollect, black pad will tend to favor one small area or pad of several boards while not effecting its neighbors - or is my recollection inaccurate?  Just the musings of a guy who worked in fab before most of it was sent offshore. 

Another question:  Are any UV solder masks available in spray cans?  I would like this for a short time for a special application.

George

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