We have done some reliability testing on Ni plated vias.  The affects and
impacts of the Ni plating depend highly upon the thickness and continuity of
the Ni plating.

In summary, Thicker layers of Ni, which are free of voids with the high Tg
resin system we use, show that the ability of the pth to withstand thermal
stresses increases.  Also, corrosion concerns go away.

The area of concern is getting that perfect Ni coating.  Many electroplate
processes do not have enough throwing power to deposit enough Ni in the hole.
Also, if you get a  bubble void in the Ni, the stress of thermal expansion is
concentrated in a smaller  region of the Cu, making failure occur much sooner.
Given different intentional Ni thickness' we have been able to double the life
of the Cu pth, or half it.  A bubble void in the Ni can bring it to nearly 0.

So, the key variables that need to be addressed include;
 - Plating thickness
 - Particular Resin and its Z expansion
 - Plating quality (freedom from thin spots, voids, etc.

My personal recommendation is that if you have high aspect ration product
(>7:1), unless you have exceptional process control, you may not want to try
Ni.  For thin product it works fine.  The telecommunications industry is
practically all Ni/Au as  a surface finish on such boards as cell phone
boards.  These low aspect ration products are less prone to the thickness and
voiding concerns.



Jim Herard
KBL, Product Quality Engineering
IBM Microelectronics Endicott
t/l 857-7026

referenced note:

------------------------------

Date:    Wed, 8 Jul 1998 11:59:43 -0600
From:    "Signorelli, Paul" <[log in to unmask]>
Subject: Nickel Plated Via's

Has any one seen any reliability data for Nickel/Gold  Plated Via's ?
This process is used to prevent copper corrosion from 'air bubble' plating
defects, plating residues and from flux residues after assembly.

Paul Signorelli
Reliability Engineer
RW Systems
Fax 719-3822520

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