Performance of New Copper Based Metallization Systems in an 85°C 80-Percent RH Cl 2 Contaminated Environment

Abstract

The performance of TPCNA (Ti-Pd-Cu-Ni-Au) and TCN+A (Ti-CuoNi+Au in selected areas only) meta!lizations in 85°C, 80-percent RH, with 0.5 to 1.8 ppm Cl 2 was compared with that of the standard TPA (Ti-Pd-Au) metallization. Encapsulated (RTV silicone rubber) and unencapsulated triple track conductor test specimens were used. Electrolytic corrosion was studied by biasing the specimens in the high humidity corrosive environment and measuring in situ leakage currents as a function of time. For the unencapsulated specimens, leakage currents increased and all samples failed by 600 h. The failure rates for TPCNA and TCN+A samples due to the formation of Cu and Ni dendrites between oppositely biased conductors were the same as for TPA which had Au and Pd dentrites. None of the encapsulated samples showed dendrite growth after ~ 1000 h. Unencapsulated TPCNA and TCN+A were less resistant to galvanic corrosion in the moist Cl 2 contaminated environment than were the TPA specimens. TCN+A failed first by Ti-Cu delamination and later by delamination of the Au due to corrosive oxidation of the underlying Ni. This latter failure mode was predominant for TPCNA. TPA conductors eventually failed at Ti-Pd interfaces. At 85°C, 80-percent RH, 1.6 ppm C!2, unencapsulated TCN+A degraded at the Ti-Cu interface ~10 times faster than unencapsulated TPA at the Ti-Pd interface. The corrosion product found on unencapsulated TPCNA and TCN+A and on Cu-NiAu external leads was identified as Cu, NiCl 2 . 3 [Cu, Ni(OH) 2 ]. The encapsulant was extremely effective in retarding galvanic corrosion. For encapsulated TCN+A and TPCNA, eventual bond failures were the result of penetration of the corrosive environment under the edges of the encapsulant. For TCN+A, encapsulation retarded the time to failure by a factor of >10. The relative resistance to galvanic corrosion in moist Cl 2 may be ranked TPA > TPCNA > TCN+A.