The use of SAC105, and many low silver / low copper variants with and without minor additives (Ni, Ge, rare earths, etc.) is being driven by makers of hand held telecom products due to studies showing improved resistance to failure in the solder ball connections during drop testing. These designs are also forcing the removal of Ni from the pad finish on both the package and motherboard substrates. I expect the use of these new SAC solders will increase over time, and spread to other types of products.
Best regards,
Leo
Leo M. Higgins III, Ph.D.
Sr. Vice President, Engg and Technology
ASAT, Inc.
13809 Research Blvd., Suite 635
Austin, Texas 78750
office phone 512-249-4758
mobile 512-423-2002
[log in to unmask]
www.asat.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stadem, Richard D.
Sent: Thursday, May 17, 2007 10:50 AM
To: [log in to unmask]
Subject: Re: [TN] Changing BGA solderballs from SAC405 to SAC105
And in all 4 of these papers discussed on the forum today, it is noted
that the MRT and TALT is required to be higher and longer in order to
achieve liquidus of the Pb-free solder ball and obtain complete
homogenity of the alloys in the solder. As a minimum, the reflow
temperature must be at least 224 deg. C for a TALT of at least 40
seconds to get full wetting on the coolest of these particular mixed
solder joints on a given assembly.
I have soldered mixed assemblies of this type myself, including with
63/37 paste with lead-free flip-chips. The reliability life was always
reduced at least somewhat. I certainly did not gain anything, and I
doubt very much that anyone else ever has in this situation.
What is forgotten or not addressed in all 4 papers is the simple fact
that the rest of the assembly (the PWB and the other components) may not
be compatible with the higher max reflow temperatures and longer times
above liquidus.
My own experience has shown that even when the process is fully
optimized, there is some variation in the temperatures such that you do
not always obtain full homogenity of the lead throughout the solder
joints of each and every mixed solder connection, but perhaps it can be
achieved on a single BGA or flip chip. The more BGAs, and the more
locations on the board that they are placed, the more you will not
always achieve complete homogenity, and the higher risk of lead-rich
areas leading to premature failure.
I do not have data showing the effects of the long term reliability of
the rest of the components on the assembly, except that several
companies have experienced PWB delamination as a result of attempting to
reflow at the higher temperatures.
Therefore, I would encourage anyone who is going to begin using
lead-free BGAs on an assembly, at least verify the PWB can withstand the
hotter temps, and it would be better to fully qualify the process by
building a small lot of assemblies first and make sure that some other
components are not going to be harmed before you jump in and start full
production.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, May 17, 2007 9:36 AM
To: [log in to unmask]
Subject: Re: [TN] Changing BGA solderballs from SAC405 to SAC105
Richard,
You should also read "Mixed Metallurgy: Reliability of SAC Balled Area
Array Packages Assembled Using SnPb Solder", Heather McCormick et al,
Celestica, given at SMTAI, Chicago, 2006.
And Dave Hillman has a paper that he gave at the International Lead Free
Conference in Toronto (I think last year), that talks about when the
solder/ball metals do not mix completely. Contact Dave for more
details.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, May 17, 2007 10:10 AM
To: [log in to unmask]
Subject: Re: [TN] Changing BGA solderballs from SAC405 to SAC105
Thank you, Ioan!
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Thursday, May 17, 2007 8:48 AM
To: [log in to unmask]
Subject: Re: [TN] Changing BGA solderballs from SAC405 to SAC105
Hi Richard,
as communicated directly to you, one of the papers was written by G.
Wenger (Mixed Alloy Solder Joint Reliability 'Sanity Check').
Unfortunately I did not save the link, but maybe he can help.
Regards,
Ioan
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Thursday, May 17, 2007 9:28 AM
To: TechNet E-Mail Forum; Tempea, Ioan
Subject: RE: [TN] Changing BGA solderballs from SAC405 to SAC105
Ioan,
Where are these studies showing that soldering of LF BGAs with leaded
solder is a good practice? Can you post a link?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Thursday, May 17, 2007 6:58 AM
To: [log in to unmask]
Subject: Re: [TN] Changing BGA solderballs from SAC405 to SAC105
Well Phil,
I haven't really been following this, but I am worried. We already have
too many customers asking us to solder LF BGAs with leaded solder and
the deal was to get the BGA balls to melt, at around 220C. I was happy
that studies started to surface showing this was good practice and the
result was reliable.
How will I be able to solder the SAC105 with leaded? And we already have
an inspector full time on the XRF, just to make sure Pb is not there.
Now I will have to ask them to measure the composition of the balls...
When will it end?
Just my concerns!
Ioan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Phillip Bavaro
Sent: Wednesday, May 16, 2007 8:31 PM
To: [log in to unmask]
Subject: [TN] Changing BGA solderballs from SAC405 to SAC105
I haven't been following the transition to use SAC105 so I would
appreciate any advice those of you who have already gone down this path
might have.
SAC405 and SAC305 was considered compatible with our SAC305 paste, but
now there is a component which is changing the solderballs to SAC105.
SAC105 has a higher liquidus temperature (226 C) than SAC305 (217 C) .
Is this going to impact our assembly processes?
Does it only tighten up the reflow process window?
Is this transition something that the majority of manufacturers of
components are going to undertake soon?
Thanks in advance,
Phil
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