Although the wetting power of SAC alloys can be less, the surface
tension  of the alloy is higher than Sn/Pb, This means that [once
wetted] they self centre to the middle of the wetted area OK.
If wetting is unevenly achieved of course then joint centre could be off
pad centre, this seems to result in a greater tendency for tombstoning
than skewing however according to print and pad geometries.


Regards

Mike Fenner

Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
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Pb-free: www.Pb-Free.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carlr Ray
Sent: Thursday, March 04, 2004 2:19 PM
To: [log in to unmask]
Subject: [TN] Self centering of lead free


Hi All,
 We are preparing to perform some experiments with lead free processing
in my facility. One of the areas we are considering looking into is the
reduce surface tension of lead free paste and the effect on devices
which have self centering characteristics such as BGAs.  Has anyone "out
there" performed these types of experiments and if so can they provide
the data and methods used?



===============================
Carl Ray
Sr. Manufacturing Engineer
13000 S. Memorial Parkway
Huntsville, AL 35807
Desk: 256-882-4800 ext. 8845
Fax: 256-882-4082
Cell: 256-990-1990
[log in to unmask]
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