I recall they found that even when the ball did not reflow the joint was

good - copper, brass or steel does not melt when you solder to it yet

the joint is still good.



Regards,

Chris

 



-----Original Message-----

From: Leadfree [mailto:[log in to unmask]] On Behalf Of Pratap Singh

Sent: 14 December 2005 16:13

To: [log in to unmask]

Subject: Re: [LF] Mixing SnPb and Pb free BGA's on an assembly



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



-----------------------------------------

This message (including any attachments) may contain confidential

information intended for a specific individual and purpose.  If you are

not the intended recipient, delete this message.  If you are not the

intended recipient, disclosing, copying, distributing, or taking any

action based on this message is strictly prohibited.



-------------------------------------------------------------------------------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
-------------------------------------------------------------------------------