Hello,
I have tested different gold thicknesses in corrosive gas environments
(after insertion cycling) and found that the 0.8 um (30 uin) thickness
to be very reliable. In my experience, using 1.3 um (50 uin) has no
downside; but it should not be necessary in your application.
The cost is dependent on the supplier. I have come across some where
the gold thickness would not affect cost and, conversely, some (e.g.
Asian suppliers) where gold thickness is a very significant cost
driver. If you specify and pay for 30 uin min., then the average
thickness will probably in the vicinity of 40-50 uin anyway.
I am puzzled, however, by the lack of a nickel barrier. The nickel
prevents copper diffusion through the gold which could create
long-term reliability problems e.g. high contact resistance. Although
a harsh environment would exacerbate the situation, I believe that,
over time, the copper would diffuse to the gold surface regardless of
the environment.
The rate of copper diffusion is greatly accelerated by temperature,
such as those experienced during wave solder and reflow. That alone
might be enough to get some level of copper to the contact surface. Do
you (or anyone else) have experience and/or test data on gold contacts
in which the nickel was eliminated?
At any rate, I would think that using nickel with 30 uin of gold would
cost the same or less than no nickel and 50 uin of gold and would
provide a contact surface with demonstrated excellent reliability
characteristics. So, why eliminate the nickel?
Also, I know that 600D, Section 4, listed the gold thickness
requirements for each class. However, I can't find the specs in 600E.
Are they there somewhere????
Regards,
Denis Mori
Hewlett-Packard
______________________________ Reply Separator _________________________________
Subject: [TN] Gold thickness - Edge
Author: Non-HP-colin.weber ([log in to unmask]) at HP-Roseville,mimegw3
Date: 6/30/98 8:58 PM
Folks,
I have been reviewing comments from past emails to the Technet forum
w.r.t. gold finishes on edge connectors.
I have concluded I should not require a nickel barrier for my application.
This could be qualified by noting the board will not be used in harsh
environments or be inserted more than several times in it's lifetime.
However I am still left wondering about the thickness of the hard gold
finish. In the past I have specified, for Class3, 1.3um. However, the
product shall be used in a class 2 environment.
Are there any disadvantages in using 1.3um (particularly since the IPC
standards state 0.8um for class 2), apart from cost?
Regards,
Colin Weber
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