The trends in integrated circuit packaging technology are toward high speed, high density, reliability, and low cost. These demand the improvement of material formulations and processing technology. Among the thick-film materials systems, conductor materials generally represent an important and the most expensive element. Therefore, attention has been centered on the performance of the fired metal film and its cost. Silver and palladium (Ag/Pd) conductors are important components of thick-film paste technology. Thick-film Ag/Pd conductors find applications in many aspects of electronics and electronic packaging, such as hybrid microcircuits, multichip modules, packaging for integrated microcircuits, and in passive electronic components such as multilayer capacitors, varistors, and inductors. In this paper, the performance and properties of fired Ag/Pd films are discussed through their physical and chemical aspects. The final film properties are correlated to a number of factors, including thermodynamics and kinetics of Pd oxidation during burnout and firing; chemical and physical reaction of the Ag/Pd with the ceramic substrate, organic vehicle, and solder; Ag diffusion and migration; B. B. Ghate-ontributing editor Manuscript No. 194446.
Silver metallization pastes for crystalline silicon PV cells containing nanosized metallic zinc were found to be superior to commercial pastes containing micrometer-sized metallic zinc and micrometer sized zinc oxide in terms of efficiency and firing window. Efficiency performance decreases as the size of the particles increases: nano-Zn > 3.6 μm Zn > 4.4 μm Zn. Advanced electron microscopy techniques were used to investigate the interfacial microstructure between the front-side contact and the Si emitter of nanosized zinc additive based cells fired at temperatures from below to above optimal. These microstructural observations confirmed the possibility of a tunneling mechanism of current flow (a "nano-Ag colloid assisted tunneling" model) in the absence of Ag crystallites. Contact resistance maps were used to guide sampling, leading to a better understanding of the relationship between microstructure and contact resistance. Low contact resistance and higher cell efficiency, especially at under- and overfiring temperature conditions, are due to more uniform silicon nitride etching obtained through the use of nanosized metallic zinc additives.
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