Jorge,
        We are currently using "immersion white tin" very successfully. The nice thing about it from our fab house point of view is that it runs through their normal line process. They have strongly encouraged it. We like the very flat surface and have been using it in place of immersion gold. We are being encouraged to try using it in some of our RF layouts but the engineers are apprehensive about using tin in high frequency applications. I don't completely understand the issues.
        One word of caution. We also design PCBs with large metal areas that contact and ground machined aluminum covers and shields for EMC. We need very flat surfaces to get a good contact seal between the covers and the PCB. Since I have been unable to get good information on the long term oxidation effects of the tin. I am afraid of an oxidation  build up over time causing resistance and or surface abnormalities between the metal covers and the tin. Of course pads and other metal areas are either covered with solder or soldermask so the tin is not exposed to the air for oxidation.
        Hope this helps.

Richard Weiner

-----Original Message-----
From: Jorge A Rodriguez [mailto:[log in to unmask]]
Sent: Thursday, February 10, 2000 8:02 AM
To: [log in to unmask]
Subject: [TN] White Tin PWB


We are about to start using immersion tin PWBs (white tin) ,  the boards we
currently use are HASL and OSP. Are there any changes with the SMT process,
component termination finish or reflow process when white tin boards are used. I
know that white tin provides a better pad finish than HASL, similar to OSP, but
wihout the organic coating.  Any comments.


Any iformation would be appreciated.


Jorge Rodriguez
Process Engineer
Conexant Systems Inc

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