Lee,
I would be interested in the resistivity measurement you did over time...
Also the pin yield strength verses the L/D ratio...
I know a bunch of telcom backplanes that were built with the type of construction you are talking about that have proven to be extremely reliable.
But if you add vibration(shock) to a deep thermal cycle which may be more typical of a mil app than al bets are off... I have seen pins crack and joints shear, even after just deep cooling cycles because of thermal expansion differentials... Without knowing where or when the PCAs will be used and the knowing the variations in process controls I would want to build the best possible interface...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
Sent: Monday, January 11, 2010 5:18 PM
To: [log in to unmask]
Subject: Re: [TN] Using Pressfit connectors on an Immersion Silver PWB
Paul
In the application I am familiar with the copper thickness of the
barrels was a nominal of one mil. Even after cycling the pins in and out
of the barrels we did not break through the copper. We did 40 year life
testing and found press fit pins in bard copper was a very robust
design. many of these boards have been in uncontrolled environments for
30 years and I am not aware of any issues.
Best regards
Lee
J. L. Parker Ph. D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: Paul Edwards<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Monday, January 11, 2010 5:06 PM
Subject: Re: [TN] Using Pressfit connectors on an Immersion Silver PWB
Since you have used press-fit connectors with ImAg in other
applications, then I can assume you are using press-fits designed for
thinly plated Cu barrels...
But is mil apps since the environments are typically more extreme I
would consider something other than ImAg... The Press-fit will cut
through to the Cu and provide an exposed channel of Cu and Ag... This
gives moisture a way to penetrate not only the barrel but also the
solid-solid metal joint interface from the weakest plane, the sliding
plane...Mechanical movement then will leverage this plane generating
micro-cracks then micro-voids which in the presence of moisture and
current would cause corrosion... This will lead to joint failure, or at
worst case, an intermittent failure...
I would stick with solder first then Ag-Ni...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, January 11, 2010 1:11 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [TN] Using Pressfit connectors on an Immersion Silver PWB
Has anyone experienced any issues with using pressfit connectors on a
circuit board that has Immersion silver finish? Do I need to worry
about
any tarnishing inside the pressfit connector holes? Since there will
be
no solder, the holes will remain open, and thus I was wondering if
there
have been any issues with this.
I am considering using immersion silver as a finish for a high
reliability design, and I have never had issues using it with
thousands
of medical and military and other applications, including
telecommunication blades where pressfit connectors were used. However,
this is a military application, and I want to know if there are any
potential issues before I commit to using it for this application.
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