I may be overlooking something, but why do you consider it is necessary to
reflow the BGA balls when using a eutectic solder paste?  Considering a
ceramic BGA with high temp solder balls, the solder balls are not heated to
reflow.

There exist a possibility of reflowing the lead-free solder balls during a
normal eutectic Sn/Pb reflow profile, but regardless, the eutectic solder
will still form its intermetallics with the PCB in the normal manner, as
well as wetting to the high tin metal of the lead-free BGA balls.

Ryan Grant

-----Original Message-----
From: Phil Bavaro [mailto:[log in to unmask]]
Sent: Friday, January 17, 2003 10:31 AM
To: [log in to unmask]
Subject: [LF] Lead-free reflow process issues


All temperatures mentioned in ths email are intended to be degrees
Centigrade and at the solder connection in question.

We are having to deal with one particular supplier of a very popular chip
who only provides their device in a Lead-free package.
It is a fine pitch BGA (0,5 mm) and the alloy of the solderballs melt at 221
C.

In a normal world, we would maintain the temperature of the assemby about
25 degrees hotter (246) and hold it there for at least 15 seconds.
But on this assembly,  the rest of the parts are not rated for a reflow
exposure above 230 C.

So the compromise is looking like we will run the assemblies at 230 C which
is about a ten degree increase from the normal processing.
Hopefully we can hold it long enough at that temp so that all the lead gets
distributed evenly in the solderaball.

My questions are:

        1)  How long do I need to keep the solder balls at 230 BGAs? 15
seconds,
39, 60?

        2)  Has anyone else encountered a lead -free BGA on their Sn 63 line
and
how do you deal with it?

        3)  What testing is recommended for Environmental Stress Screening
to
ensure that the time at max temp is adequate?



Thanks in advance

Phil

----------------------------------------------------------------------------
---Leadfee Mail List provided as a free 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 delivery of Leadree for vacation breaks send: SET
Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
----------------------------------------------------------------------------
---

-------------------------------------------------------------------------------Leadfee Mail List provided as a free 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 delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-------------------------------------------------------------------------------