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May 2012

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TechNet E-Mail Forum <[log in to unmask]>, Pete <[log in to unmask]>
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Fri, 25 May 2012 12:42:39 -0500
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Low - P gives the fabricator less margin for error, the assembler, more margin.  Hgih P is the opposite.  But the margin on low P is VERY thin.    The change to mid-P is a big reason why black pad has become far less prevalent.  I would not accept <7% anymore

Higher P causes a near self limiting gold corrosion, keeping the gold from corroding the Nickel (black pad).  But it does concentrate the P near the Ni/Sn Intermetallic formation of the joint, making dark line defects (brittle P layer) easier to create during reflow.  High P also allows thinner gold, less to dissolve into the IMC.

Pete

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