Hi Ioan,
IAs I said before, I don't think that the liquid/molten paste were in
direct (intimate) contact with the balls. Otherwise dissolution of still
solid balls in liquid/molten paste should have begun and you should have
seen some connection/necking/bridging between the balls and paste. As
soon as either one (BGA balls or paste) becomes liquid, amalgamation
process starts and the rest is just a matter of time above liquidus (to
be exact, the liquidus temperature will be changing, following changes
in the chemical composition of new alloy "solder paste + balls
material".
Regards,
Vladimir
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Thursday, November 16, 2006 9:12 AM
To: [log in to unmask]
Subject: [LF] Separation in BGA joints
Thanks to everybody who replied, including the non-metallurgists ;-} I
have certainly learned things!
I think the secret lies in that 270C melting point. I use a regular
SAC305 soldering recipe (right semantics, not profile; see, I got this
one Werner), hence the 240C target peak. Of course this will not move
the 1.75%Cu alloy.
One thing is that the component data sheet says the alloy is SAC305. But
it also recommends 260C for peak temperature. I find this very weird,
since somebody told me we need to solder at MP + 20C, so my 246C should
be more than OK. Not to mention that many ICs on the board are speced
per J-STD-020C for max peak of 250C.
Question 1: why this 260C recommendation, when 240C should be OK?
Then, I would like to know more about the case of high temp solder
balls. Why a joint will be formed around 210C between SnPb paste and
90/10 balls and the solder would not wet at 246C on a 270C solder ball?
The flux cushion is there in both cases. And why the SAC ball should
melt anyway, if solder wets on 90/10, why shouldn't it wet on other
higher temp balls? Is it because the Pb goes into solution with the Sn
whereas the high concentration Sn-Sn interfaces absolutely have to mix?
Thank you very much,
Ioan
------------------------------------------------------------------------
-------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
------------------------------------------------------------------------
-------
-------------------------------------------------------------------------------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
-------------------------------------------------------------------------------
|
