Tin plate has a problem with the potential for tin whiskers. The whiskers are
long single crystals that can cause shorts. Some tin plate manufacturers can
avoid the potential for tin whiskers by alloy additions or other
formulation/plating process improvements. The whiskers can be prompted by
thermal history and even by stress. People often avoid pure tin plate because
it can be risky.

---------------------------------------------------
Mike Wolverton /Microwave Advanced Technology /AT&C
TI 
E-mail: [log in to unmask]

------------------
Original text

From: Jack Olson <[log in to unmask]>, on 6/24/97 11:58 AM:
To: Bruce Boyes <[log in to unmask]>
Cc: [log in to unmask], [log in to unmask]

Bruce Boyes wrote:
> Tin plate is dipped in a plating tank. Soldercoat is dipping in molten
> solder. Solder is usually a much thicker layer and harder to control, so
> expect some blobs due to surface tension of the solder, I guess. Solder is
> also a tin/lead alloy whereas tin plate is presumably, well, tin.

I can certainly understand that, but I am wondering why we have never
tin plated digital SMT boards at the last three or four companies I have
worked with. One less thermal shock to the board and flatter lands, so
what is the down side? Why not ALWAYS use it over soldercoat? What am I
missing?



> Supposedly, you can start to see the effect even at 33 MHz or more on fast
> digital lines with sharp vs rounded corners. 

Thank you for responding, but I was really looking for data on round
versus chamfered.

onward thru the fog....						Jack

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