Jim,
For leadframe-based packages, the main concern with use of Pb-free components in a SnPb process is with SnBi finish. Users are concerned about reliability issues related to mixing of Bi with Pb. However, SnBi is not the primary finish being used. The 2 primary Pb-free finishes being offered are nickel-palladium-gold (NiPdAu) for preplated leadframes and tin (Sn) for post mold plating. Both NiPdAu and Sn finished components are solderable with both SnPb solders and SnAgCu solders. TI has published an app note specifically focused on soldering performance of NiPdAu finished components with both SnPb and SnAgCu solders. Also included is some data using SnPb finished components. You can view this specific app note at the following location: http://focus.ti.com/docs/apps/catalog/resources/appnoteabstract.jhtml?abstractName=szza026
For array packages (PBGA, etc) most suppliers are offering packages with both SnPb and SnAgCu (Pb-free) balls. Most recommend that SnPb ball options be used for SnPb soldering while the Pb-free ball options be used with Pb-free solders only. There is technical data that supports this for array packages.
As for tin whiskers, this is a major issue being investigated right now. Many IC suppliers have plans to use Sn finish for their leadframe packages. There are industry consortia that are trying to understand the fundamental mechanisms of whisker growth and to develop a whisker test method. NEMI is a leader in this activity (http://www.nemi.org/projects/ese/tin_whisker_activities.html). There are numerous technical papers on this topic. NASA has a site on this topic (http://nepp.nasa.gov/whisker/).
Best regards,
Doug Romm
Texas Instruments
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Marsico, James
Sent: Thursday, March 11, 2004 2:28 PM
To: [log in to unmask]
Subject: [LF] lead-free components with PbSn process
Good Day All:
I've posted a similar question on technet, but I thought this forum would be
more appropriate.
What are the problems, if any, with using lead-free components with a PbSn
SMT process? Are there any compatibility issues? How about long-term
reliability for military products?
Also, is anyone concerned with the influx of components with pure tin
finishes with regard to tin whiskers?
One more thing... are there concerns that "custom" components, specified
with a PbSn finish, might become extinct (DMS, diminishing manufacturing
source)?
Thanks for your advice,
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
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