Pratap,

This example may not apply to this discussion, since in your example
there might have been more than enough Bi to create the ternary alloy.
A 2-4% Bi/remainder Sn mix on a component lead is much thinner than
Sn58Bi coated (not plated, right?) boards.  Why in the world would
someone provide Sn52Bi boards is beyond me?  Was this a test case to see
what would happen, or was it a production board (very unlikely)?
Doesn't seem to be a real world example, but then again, what do I know?

Turning out to be a top notch discussion!  And if anyone runs across any
test results of Bi in Pb-bearing or Pb-free soldering, I would be
interested!

Keep up the good work guys, gals, and whoever's not covered in the first
two!
Roger

-----Original Message-----
From: Pratap Singh [mailto:[log in to unmask]] 
Sent: Thursday, October 13, 2005 1:25 PM
To: (Leadfree Electronics Assembly Forum); Roger Stoops
Subject: Re: [LF] Leadfree Processing temp requirement

Hello Dave and Roger
Many good points raised about how Bi may affect solder joint. There is
an interesting summary  about this observation on page 215, section
6.6.2 & 6.6.3 Tin Bismuth Solder in the book 'Failure Modes and
Mechanisms in Electronic Packages', Chapman & Hall 1998.. The results
are based on  SnBi (42/58 alloy that was plated in PTH as part of the
board finish and a connector was soldered using standard Sn/Pb (63/37)
alloy. Thermal cycle test was 0C-100C and results were catastrophic. As
the cycling proceeded, connectors pins started falling. See pictures
6.60 and 6.61 on pages 216 and 217 of the book. SnPbBi ternary alloy
just oozed out of PTH in a snow flake type of mini balls.  There is no
mention of the amount of Bi present in PTH joints

_____________________
pratap singh
Tel./Fax: (512) 255-6820
email: [log in to unmask]
www.rampinc.com

-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-------------------------------------------------------------------------------