Electrochemical migration is caused by the adsorption of water and the bias voltages between the electrodes or pads which form an electric circuit or in the solders used to connect the parts. This work focused on the elucidation of the mechanisms of electrochemical migration of pure Sn, Sn37Pb, and Sn55Pb solders in electronics. The electrochemical migration behavior was discussed on the basis of the polarization behavior of SnPb solders. After the water drop test, the time to failure decreased with increasing Pb content in Cl solution and increased with increasing Pb content in SO 4 2 solution. In the case of the SnPb solder alloys, the pitting potential, the passive current density, the cathodic current density and the efficiency of cathodic deposition of the alloying elements were closely related to the resistance of the electrochemical migration.
Biometals need high corrosion resistance since metallic implants in the body should be biocompatible and metal ion release should be minimized. In this work, we designed three kinds of super stainless steel and adjusted the alloying elements to obtain different microstructures. Super stainless steels contain larger amounts of Cr, Mo, W, and N than commercial alloys. These elements play a very important role in localized corrosion and, thus, their effects can be represented by the "pitting resistance equivalent number (PREN)." This work focused on the behavior which can arise when the bare surface of an implant in the body is exposed during walking, heavy exercise, and so on. Among the experimental alloys examined herein, Alloy Al and 316L stainless steels were mildly cytotoxic, whereas the other super austenitic, duplex, and ferritic stainless steels were noncytotoxic. This behavior is primarily related to the passive current and pitting resistance of the alloys. When the PREN value was increased, the passivation behavior in simulated body solution was totally different from that in acidic chloride solution and, thus, the Cr(2)O(3)/Cr(OH)(3) and [Metal oxide]/[Metal + Metal oxide] ratios of the passive film in the simulated body solution were larger than those in acidic chloride solution. Also, the critical current density in simulated body solution increased and, thus, active dissolution may induce metal ion release into the body when the PREN value and Ni content are increased. This behavior was closely related to the presence of EDTA in the simulated body solution.
Electrochemical migration occurs via electrochemical processes. When a water film forms on the electric circuit and then a bias voltage is applied, the metallic ions dissolve from the anode and move to the cathode. At the cathode, the metallic ions react with the electrons and then form dendrites. Thus, a short circuit failure of the electronic components occurs. This study focuses on the relationship between the electrochemical migration (ECM) susceptibility of SnPb solders and the composition of the dendrites on the basis of electrochemical techniques. It was found that the ECM susceptibility of SnPb solder alloys was affected by the chloride and sulfate ions. After the water drop test, the composition of the dendrites was primarily Pb mixed with Sn, regardless the dissolution/composition ratio of the solder alloys. However, only Sn was detected in the dendrites formed in the acidic solution. The dissolution of the metal from the anode influenced the failure time, and the pH of the corrosion environment significantly changed the composition of the dendrites formed on the cathode. The composition of the dendrites was proven to be closely related to the cathodic deposition efficiency of the ions dissolved from the anode.
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