Chris,
  NPL paper shows that mixed solders (LF mixed with SnPb) provide better reliability than SnPb alone. This will happen when there is reflow of both solders.

  The question being asked, however, is different. Some folks want to use a LF solder ball package in SnPb reflow profile. LF will not reflow in 225 - 235 C range. Visually joint may look OK because SnPb has reflowed covserin the pad and LF solder ball. LF solder ball, however, has not reflowed. That produces a weak unreliable joint.

  One may have to use rework type approach as shown by NPL data where the reflow of LF solder ball is assured by using the right thermal profile.

  __________________________


pratap singh
tel./fax 512-255-6820
email:[log in to unmask]

-------------------------------------------------------------------------------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
-------------------------------------------------------------------------------
web:www.rampinc.com