The electronic packaging industry has been using electroless Ni͑P͒ / immersion Au as bonding pads for solder joints. Because of the persistence of the black pad defect, which is due to cracks in the pad surface, the industry is looking for a replacement of the Ni͑P͒ plating. Several Cu-based candidates have been suggested, but most of them will lead to the direct contact of solder with Cu in soldering. The fast reaction of solder with Cu, especially during solid state aging, may be a concern for the solder joint reliability if the package will be used in a high temperature environment and is highly stressed. In this work, the reaction of eutectic SnPb solder with electrodeposited laminate Cu is studied. Emphasis is given to the evolution of the microstructure in the interfacial region during solid state aging and its effect on solder joint reliability. A large number of Kirkendall voids were observed at the interface between Cu 3 Sn and Cu. The void formation resulted in weak bonding between solder and Cu and led to brittle fracture at the interface in the ball shear and pull tests. The experimental results indicate that a barrier for Cu diffusion may be needed between the solder and the type of Cu used in the test vehicle for the packages that will experience high temperature ͑Ͼ100°C͒ and high stress.

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The low-temperature {1. 3 -20.0 K) high-magnetic-field (0 -10 T) heat capacity and the magnetization and magnetic susceptibility (1.7 -300 K) of the strongly Pauli paramagnetic RCo2 (R =Sc, Y, or Lu) compounds with the MgCu2-type structure were measured. The heat-capacity results for ScCo2, YCo~, and LuCo2 show that the electronic specific-heat constant decreases with increasing magnetic fields (by 7%, 4%%uo, and 10', respectively, at 10 T). For YCo2 the coefficient of the T term (P) in the heat capacity is found to increase by 18% at 10 T, but for ScCo2 and LuCo2 P remains constant within experimental error. Analyses based on several theoretical models of the quenching of spin fluctuations by high magnetic fields suggest that the characteristic spinfluctuation temperature is -20 K for ScCo2, -35 K for YCo2, and -16 K for LuCo2. The magnetization and the field dependence of the magnetic susceptibility of the same samples as used in the heat-capacity measurements indicate the presence of ferromagnetic impurities in the samples, but the estimated concentrations are sufficiently low that they probably have no effect on the observed heat capacities. Maxwell's thermodynamics relationship between the field dependence of the heat capacity and the temperature dependence of the magnetic susceptibility has been examined.

This paper reports on a study of the reaction of solder with the electrolessnickel with immersion gold (ENIG) plating system, and the resulting interfacial structures. A focused-ion beam (FIB) was used to polish the cross sections to reveal details of the microstructure of the ENIGplated pad with and without soldering. High-speed pull testing of solder joints was performed to expose the pad surface. Results of scanning-electron microscopy/ energy-dispersive x-ray analysis of the cross sections and fractured pad surfaces support the suggestion that black pad is the result of galvanic hyper-corrosion of the plated electroless nickel by the gold plating bath. Criteria are proposed for diagnosing black pad of ENIG plating.

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