Franklin,
My Tin whisker concern is derived from the connector only.
Immersion Tins such as Omikron are unfortunately not a qualified finish for my company.
Due to the type of design we do and the fact that it required over 2 years of testing to qualify IAg, I have not tried to add ISn to our finishes.
I personally have no concerns of metal migration from the Omikron finish (I have studied up on this), but I also work with a bunch of RF Engineers who seem to feel it will effect their black magic.
Have you ever tried to convince a RF Engineer to change their ways (sometimes I think I would rather herd cats)?
Unfortunately due to the collapsing window I have for qualification of these new RoHS products I am forced to use what I have and am just looking to find the "warm and fuzzy" feeling that I won't be causing field failure issues with this new combination.
Thanks for your input,
FNK
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Franklin Asbell
Sent: Tuesday, October 04, 2005 8:53 AM
To: [log in to unmask]
Subject: Re: [TN] RoHS Pressfit Connector
I'm curious why Immersion Tin is not an alternative for you, or, is that why
you wrote tin whiskers?
Today's immersion tins, Omikron more so than FST, is a suitable coating for
press-fit product that virtually eliminates whiskers. I would say the risk
of whiskers with Omikron is no better, or worse, than Enig or IAg...yes, I
know what I just wrote...
I am surprised Florida Cirtech (and I only mention them as I have not dealt
with Enthone's FST since it was Dexter) has not been more vocal about their
product.
When 35 - 40 micro inches are applied it makes a fine surface for multiple
thermal cycles and any press-fit product. Plus, it is less expensive than
the other two you mentioned.
And no, I am not a spokesman for Florida Cirtech, just someone who has used
their product for many years and am familiar with it's capabilities and
limitations.
I think someone should write an article about this, explaining the
differences (chemistry, grain structure, dendritic growth susceptibility ,
etc) to dispel the fear of today's bath's. Post this article in fabrication
and assembly mag's both hard copy and electronic.
All testing I've performed, many hours, many designs, I was only able to get
growth over the Omikron surface by introducing contaminates "at the
completion" of testing. It just would not whisker...
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Frank Kimmey
Sent: Tuesday, October 04, 2005 10:37 AM
To: [log in to unmask]
Subject: [TN] RoHS Pressfit Connector
A little help would be appreciated here.
I have been tasked with selecting the "right" RoHS finish for our PCBAs.
Until now I think it's been pretty easy, just choosing between ENIG and IAg.
Now I have run into an issue that has me unsure.
Due to a short window (no time to experiment) and materials available here
is what I'm up against.
I need to convert an assembly that uses a 50+ pin pressfit connector from
Sn/Pb over Ni going into HASL.
The new connector is Sn over Ni and cannot be sourced elsewhere (customer
requirement)
The new PCB can be either ENIG or IAg.
The connector has a customer required "no solder to be used".
My worries are:
1. How bad will tin whisker issue get? And is there anything I can do?
2. Will IAg have more problems due to environmentals (sulfur, etc.)
3. Since we call out 40 to 150 u" of Ni in our ENIG will barrel damage
likely rear its ugly head?
This connector does require considerable force to install (in this case
press fit means equipment to be used).
I think that once pressed in, then the connector to copper mechanical
connection may be enough.
So I am leaning towards IAg.
Your thoughts and comments are highly appreciated.
Thanks,
FNK
Frank N Kimmey CID+
Principal PCB Designer
Powerwave Technologies Inc
Office 916-941-3159
Fax 916-941-3195
Cellular 916-804-2491
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