AgCrO ₂ formation mechanism during silver inner electrode and Fe–Si–Cr alloy powder co-firing in metal multilayer chip power inductors

Multilayer Fe–Si–Cr alloy chip power inductors have the benefits of a smaller, thinner profile, lower DC resistance and higher rated current. During metal multilayer power inductor co-firing, Fe–Si–Cr alloy powders react with the inner electrode, silver, to form a large amount of hexagonal flaky AgCrO ₂ . The p-type semiconductor, AgCrO ₂ , will cause co-fired Fe–Si–Cr alloy multilayer chip power inductor insulation degradation, hence reducing the power conversion efficiency due to the increase in eddy current loss. The AgCrO ₂ forming mechanism is investigated in this study. It was observed that silver reacts with the Fe–Si–Cr thermal grown oxide layer, Cr ₂ O ₃ , and subsequently leads to the formation of Ag ₂ CrO ₄ when the temperature is lower than 650 °C. The formed Ag ₂ CrO ₄ with low melting temperature then volatilizes at higher temperatures through the pore channels to react with the volatilized Cr ₂ O ₃ to form the AgCrO ₂ . AgCrO ₂ will cause Fe–Si–Cr alloy multilayer chip inductor resistivity and breakdown voltage degradation.