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November 2000

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Subject:
From:
George Milad <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 28 Nov 2000 11:38:20 EST
Content-Type:
text/plain
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Ben,

Electroless Nickel/Immersion gold (ENIG) is a surface finish in its own
right.  It does not involve electroplating after. In most shops it is applied
after soldermask cure, others apply the finish then follow with the
soldermask application and cure.

Electroless nickel (120 - 200 uins) is the diffusion barrier and the
soldering surface.  The immersion gold surface  (2 - 4 uins) is there to
protect the Ni from passivation and/or oxidation until assembly time.
Immersion Gold is POROUS.  At assembly the gold is dissipated into the
solder, and a Nickel /Tin solder joint is formed.

A defective/corroded Ni surface "Black pad" will not form a good solder
joint. The Black pad issue is presently well understood by your supplier and
can be avoided.
A contaminated gold surface (soldermask, organic residues etc.) will also not
give a good solder joint.

George Milad
Technical Mkt. Mngr
Shipley Co.
(516) 868-8800 ext. 269

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