THAT Corporation Finishes
Beginning late in 2014, THAT Corporation will gradually change the lead finish on all ICs from Nickel-Palladium-Gold (Ni-Pd-Au) plating to matte Tin (Sn). Until all our products are converted, and our stock of Ni-Pd-Au parts is exhausted, you may receive products with either plating. We expect this to take several years. Additionally, effective with orders placed from the beginning of 2015, we will discontinue the suffixes which indicate specific lead finishes (-I representing Tin-Bismuth, -T representing Tin, and -U representing Ni-Pd-Au). After the start of 2015, all parts may be ordered using one "universal" suffix, "-U", regardless of finish. While the finish may vary, all ICs with a -U finish comply with current RoHS requirements.
Matte Tin (Sn)
Tin has good wettability/solderability over a large range of substrates, making it an excellent choice for lead (leg or pin)) finish through tin plating. Modern IC packaging methods have mitigated the tin whisker problems which previously hampered the soldering process.
Nickel-Palladium (Ni-Pd) plating was first introduced by Texas Instruments to the semiconductor industry in 1989. Nickel-Palladium-Gold (Ni-Pd-Au) is a refinement of Ni-Pd, which offers somewhat enhanced performance due to a quicker wetting time when compared to Ni-Pd and Sn-Pb finishes. THAT, along with TI and many other semiconductor companies have shipped millions of ICs using this plating combination.
Here are a two references which provide additional information about this finish option.
Romm, Lange & Abbott, "Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits", Texas Instruments Application Report SZZA026, July 2001. www.ti.com/lit/an/szza026/szza026.pdf
Abbot, "NiPd Finishes for Pb-Free Leaded components", presented at UC SMART sponsored Two-day Workshop on Pb-free Solder for Electronic, Optical, and MEMS Packaging Manufacturing, Sept 5~6, 2002.
Tin Bismuth (Sn-Bi)
THAT ICs using a tin-bismuth lead finish have lead frames made of an iron-nickel (Fe-Ni) alloy (58/42), plated with tin-bismuth in proportion 98/2. Tin-bismuth finishes offer good wettability and are considered compatible with both lead-bearing and lead-free soldering processes.
Here are a few references which provide additional information about this finish option.
Hua, Fay, et.al , "Eutectic Sn-Bi as an Alternative Pb-Free Solder", IEEE Conference on Electronic Components & Technology, pp 277~283, May 1998.
Henshall, Roubaud, Chew et. al, "Impact Of Component Terminal Finish on the Reliability of Pb-Free Solder Joints",
Renesas Electronics Corporation (formerly NEC Electronics Corporation), "Lead (Pb) –free Semiconductor Products", May 2006. www.cel.com/pdf/marcomnews/leadfree.pdf
The shelf life of Pb-free finishes used by THAT ICs is quite long. We warrant our ICs to be solderable for at least ten years after the packaging date, provided the parts are stored at room temperature without excessive humidity. The ten-year time frame is conservative based on a Texas Instruments paper that notes a shelf life of 15 years, as well our own solderability testing performed on parts which have been stored for this length of time. We reserve the right to ship parts for up to eight years from the date of packaging.
Soldering Temperature Profile
When soldering THAT's Pb-free ICs, take care to follow IPC-JEDEC recommendations for soldering temperature profiles. Peak temperatures for Pb-free ICs are higher than those which used to be used in Pb-Sn soldering. All THAT's RoHS 2 compliant parts are compatible with peak reflow soldering temperatures of 260°C, though customers must observe the temperature and time limitations specified within IPC / JEDEC standard J-STD-020D.1, "Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices".
See www.jedec.org/sites/default/files/docs/jstd020d-01.pdf, as well as other documents relating to the handling and soldering of surface mount parts at www.jedec.org.