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58 SMT Magazine • June 2015 systems can be improved and this will lead to extending their lifetimes: achievable by cooling component devices on both sides and by the se- lection of SiC-based substrates with high ther- mal conductivity. This presentation concluded with examples of SiC-based inverters for electric vehicles and the use of additive manufacturing heat sinks, all developed at Swera/IVF. The re-processing of leadless semiconductor packages and column grid array (CGA) pack- ages are part of the core business capabilities of Micross Components Ltd (Crewe, UK). Mark Walmsley discussed how lead-free terminations on a very wide range of component packages can be reprocessed at their Crewe facility into tin-lead technologies. The use of Sn-Pb termi- nations and Sn-Pb solder interconnections are known to have a higher reliability for military avionics, space, nuclear power and other critical applications—industries producing such hard- ware are exempt from the EU RoHS directives related to lead-free electronics. A new material/process for Micross involves the practice of using non-collapsible stand-offs in- corporated within the solder interconnections of area grid array packages. These have been shown by environmen- tal testing to be extremely reliable for both ceramic and plastic packages mounted onto a variety of PCB lami- nates. Where column grid ar- rays are concerned, Micross have transferred a "column last attached solder process" from IBM in the U.S. to their facility in Crewe. The so-called CLASP columns consist of 10/90 Sn/ Pb columns with eutectic Sn/Pb end fillets; they have been approved by U.S. users and will be "qualified" using UK processed packages. Don Tyler of Corfin Industries, Salem, New Hampshire, U.S., continued the theme of re- processing by describing his company's facility for converting Pb-free ball grid arrays into tin- lead by "robotic hot solder dipping." The use of lead-free terminations with tin-lead solder alloys results in weakened solder joints. This eVenT ReVIeW: (eMPS-6) continues so-called "mixed technology" is unreliable and Corfin Industries have been de-balling Pb-free BGAs using robotic systems for many years. The Pb-free spheres are removed over a solder wave in combination with forced hot air. The devices are then de-fluxed, cleaned and dried before re- balling in a programmable convection oven. Area grid array packages have been re-balled up to three times without appreciable loss of nickel or copper from their pads by dissolution into the liquid solder. Quality controls include scanning acoustic microscopy, cleanliness test- ing and solderability testing to IPC standards. Examples of all the processing steps were de- scribed and illustrated by means of a video film and photomicrographs of metallographic cross- sections. Fernando Perez Garcia (CRISA, Airbus De- fence and Space), Tres Cantos, Spain, delivered a challenging, if not controversial, talk con- cerning the complexity of gaining ESA qualifi- cation for surface mount technolo- gies to be used for spacecraft. He discussed whisker mitigation methods and the possible use of Level 2C solder assem- bly philosophy per GEIA- STD-0005-2, where lead-free tin finishes are permitted un- der certain well defined cir- cumstances. Antti Rautiainen of Aalto University, Finland, has spent some time during his doctor- al candidacy at ESA studying solid-liquid inter-diffusion bonding for MEMS sensor inte- gration. This technique is based on the formation of intermetal- lic compounds between high and low melting point alloys. So-called SLID bonding offers high re-melting temperature intercon- nections with low processing temperatures and small footprints. Rautiainen compared other conventional metal bonding processes with SLID both in terms of manufacturing routs and resultant microstructures—mainly for Cu-Sn and Au-Sn final bond structures. He discussed reliability in terms of strength and environmen- tal testing. The samples produced showed some artICle area grid array packages have been re-balled up to three times without appreciable loss of nickel or copper from their pads by dissolution into the liquid solder. " "