Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"Anna Wierzbicka-Miernik"

Morphology and chemistry characterization of intermetallic phases in (Cu + 5 at. % Ni)/Sn-Ag-Sn/(Cu + 5 at. % Ni) interconnections

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Nowadays, finding the lead free substitutes for the Pb-high content solder materials for the use at the higher (250÷350°C) temperature [1÷6] as well as development of the new soldering techniques in the electronic industry are of prime importance in the environment friendly technologies. The diffusion soldering is the alternative joining technique which results in the interconnections characterized by the high thermal stability combined with relatively low-temperature of soldering [7÷10]. However, in order to apply this technique in the production line it is necessary to shorten the time to several seconds of soldering process. Recently, number of experiments have been performed in order to find suitable additions which could accelerate the diffusion during the soldering process [11, 12]. The presence of the Ni addition, even in very small amount (~5 at. %), in the Cu pads caused the suppression of the Cu3Sn phase formation in the reaction zone at substrate/solder interface. Additionally, the nickel significantly changed the morphology of the Cu6Sn5 intermetallic compound growing in the joints and which was even more important increased the rate of its formation. However, some discontinuities were present in the centre of the interconnections (for example Fig. 1d in Ref. [13]). The same problem was reported by Chung et al. [14] in the case of Cu/Sn/Cu/Sn/Ni diffusion couples aged at 200°C for different times. The discontinuities are described as the ‘‘Kirkendall voiding’’. Their occurrence is caused by the agglomeration of excess vacancies as the result of the different intrinsic diffusivities of Cu and Sn in the forming intermetallic phase [15]. The amount of Sn diffusing across the (Cu, Ni)6Sn5 phase is more than Cu [16]. It is also known that the voids are mostly generated within Cu3Sn layer, but rarely within the Cu6Sn5 layer [17÷23]. However the lack of Cu3Sn phase in our previous studies [13] was [...]

Microstructure and mechanical properties of the Cu/SnAuCu/Cu joints

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The European Union regulations forced the manufactures to limit the use of certain hazardous substances such as cadmium and lead in the electrical and electronic equipment and also make them responsible for its storage and recycling [1, 2]. In a consequence the lead-free interconnection technology is one of the most active branches of the nowadays materials science. PbSn replecements are mainly the tin alloys, among which a special class are those consisted of tin and noble metals such as copper, silver and gold. They are possesing two characteristic features - the high melting point and high concenteration of Sn compared to that of eutectic PbSn. Moreover, the composition of the lead-free solders can be described as eutectic or near-eutectic, which ensures the best manufacturability. The microstructure of these solders is a mixture of tin and the intermetallic phase (IP). Since both mechanical and electrical properties of the tin are anisothropic they are also anisothropic in the case of eutectic solders. Therefore, the intermetallics may take a form of the inhomogenous structures (for example Ag3Sn in the shape large plate-like crystals). To avoid of such IP creation the concentartion of silver in SnAg solder should be less than 3% wt. and copper should not go over than 0.7% wt. in SnCu solders. In the case of SnAu solders gold must not exceed the value of 5% wt. otherwise it leads to the formation of AuSn4 phase which causes britlle “cold" joint. Ternary solders are mainly SnAgCu solders (SAC) where the amounts of silver and copper (corresponding to the eutectic composition) are 3.5±0.3 and 0.9±0.2 (wt. %), respectively [3÷5]. Other ternary solder is SnAuCu alloy which may be used as a joining material for the joints in so-called noble electronics. They are applied in devices with the highest degree of reliability, such as biomedical devices. It should be noted that such products after their exploitation und[...]

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