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February 1999

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From:
Circuit Connect <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 2 Feb 1999 09:32:46 -0500
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Any of the immersion coatings would perform well regards improved (tighter)
diametric tolerance versus solder-coated barrels, and as gold and OSP have
already been commented upon I'll add white (non porous) immersion tin as
another alternate choice.

Our experiences with white tin are in complete agreement with IBM's 1984
study of that finish ("Immersion Tin: It's chemistry, metallurgy and
application in electronic packaging technology", 1984, Z. Kovac, K.N. Tu,
IBM, IBM Joint Resource Development VOL 28 No 6.). While this paper does not
report upon press-fit pins specifically, we have a substantial number of
back panels in the field supplied to various OEM's - many in severe service
environments - with a practical history of zero line or field failures as
concerns the assembly performance of the pins.

Our clients' appreciation for white tin includes:
- allowance of PTH diametric tolerances down to +/- .0015"
- improved ductility versus nickel
- affinity for dissolution into all tin-based solder alloys
- excellent wicking
- good response in wide range of fluxes
- very low cost
- does not introduce a third metal to solder pots
- no embrittlement issues
- no environmental issues
- infinite shelf life

In addition to tin (and the previous comments on OSP and gold) silver and
palladium might also be investigated (although I have no practical
experience in the latter).

Cheers!

Bob Lazzara
Circuit Connect Tech Support
Georgia Service Bureau

TEL: 800.560.9457    FAX: 888.453.0520    BBS: 603.889.5385
alternate eMail: [log in to unmask]

-----Original Message-----
From: Jim Herard <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, February 02, 1999 8:22 AM
Subject: Re: [TN] : Press-fit with Immersion NiAu or OCC


>Press Fit with OSP (organic coating over copper such as Benzyl Trimidizole
>(sp?)) works very successfully.  However, some manufacturing process
>changes may be required depending upon the press fit pin style  and
>plating.  The lack of SnPb on the board does increase insertion forces to
>some degree.
>
>Cross sections should be taken when working with Ni/Au plated vias, as the
>Ni is not as ductile as the copper, and some barrel cracking may occur,
>depending upon pin design and forces.
>
>Hope that helps.
>
>Jim Herard
>Mail/Dept  BNLE
>Mgr, FJUW, 3rd shift Test and Inspect
>IBM Interconnect Products , Microelectronics Div
>Endicott NY 13760-5553
>t/l 857-7026
>
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