| The present work is aimed at proposing the measures how to impede the galvanic corrosion occurring between Pd outer-layer and Alloy42 lead frame matrix and at the same time the formation of microcracks by hydrogen absorption into Pd layer electrodeposited on the Alloy42 lead frame. For this purpose, charge-transfer resistance, surface morphology, surface chemical composition and electrochemical characteristics of various electrodeposited layers were investigated by using ac-impedance spectroscopy. SEM, EDS and cyclic voltammetry, respectively. From the analysis of ac-impedance spectra, it is found that introduction of the intermediate electrodeposited layers between Pd outer layer and Alloy42 lead frame improves the galvanic corrosion resistance and Alloy42/Cu/Ni/Pd-Ni/Pd structure shows the highest corrosion resistance of all structures. As the hydrogen-charging potential decreases below the β-PdH formation potential, the formation rate of microcrack on the surface of the electrodeposited outer layer remarkably increases. This is attributed to the molar volume expansion by 10% developed due to the formation of the β-PdH phase. It is suggested that the formation of microcracks in the electrodeposited Pd outer layer is hindered by employing the Pd-Ni or Pd-Au alloy as outer layer instead of the pure Pd outer layer and/or by introducing the Cu/Ni intermediate electrodeposited layer between the Alloy42 lead frame substrate and Pd outer layer. |
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