Plated copper on ceramic substrates for power hybrid circuits

Abstract

Plated copper on ceramic has been evaluated for fabrication of power hybrid circuits. The copper is plated using a semiadditive process that yields rectangular conductor cross sections. Copper thicknesses can be varied from 12 to 150 mu m depending on electrical current requirements. Typically, a 2.5- mu m nickel barrier layer and a 1.25- mu m gold layer are plated onto the copper metallization. The soldered adhesion (62Sn/36Pb/2Ag) of the metallization has been studied. No adhesion degradation was observed after storage for 1000 h at 150 degrees C or after 118 thermal cycles between -65 degrees C and 125 degrees C. The bonding of small-diameter gold-wire bonding to the Au/Ni/Cu metallization was evaluated. No reduction in bond strength ( approximately=7.5 gf) was observed after 1000 h of storage at 150 degrees C. The bonding of large-diameter aluminium wire to the Au/Ni/Cu metallization was also studied. The average initial pull strength was 560 gf. After 2050 h at 150 degrees C, the average pull strength was 499 gf, while the average after 2050 h at 200 degrees C was 438 gf. Screen printable polyimide encapsulants were used for solder masking and high voltage insulation. Electrical properties were measured. To demonstrate the use of plated copper on ceramic, the power section of a 100-W DC-DC converter was fabricated. >