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Pure copper (Cu) soldering joints with 304 stainless steel (SS) at different soldering temperatures (240–$350^{\circ }$C) were prepared by using Sn–3.5 Ag (wt.%) as a soldering filler-metal material. The mechanical properties and microstructure evolution were investigated. Sound Cu/304 SS joints were obtained by soldering at 240–$350^{\circ }$C for 90 s and the highest average joint shear strength was $\sim 39$ MPa when brazed at $300^{\circ }$C. The Cu₆Sn₅ and Ag₃Sn phases were typical intermetallic compounds (IMCs) in the joints at a soldering temperature of $240^{\circ }$C. Cu₃Sn IMCs were formed at the Cu/Cu₆Sn₅ interface as the soldering temperature increased to $300^{\circ }$C and above. Shear fracture analysis by scanning electron microscopy (SEM) with energy dispersive spectroscopy showed that the joints fractured mostly inside the Cu₆Sn₅ layers.

The miniaturisation of electronic assemblies, increasing silicon integration and device complexities have all contributed to the need to use finer package-to-substrate bonding pitches. An evaluation is presented for the technologies applicable to assembling devices with lead pitches of between 0.6 and 0.25 mm. The packages for such devices with a gull-wing outer lead-bonding format fall into three main categories. These include the various plastic quad flat packs, subminiature plastic packages supplied in carrier rings, and devices supplied on tape. Integration of these packages into hybrid or PCB-based modules poses significant technical and economic challenges. These issues are discussed and suitable manufacturing routes proposed.