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; inorganic and organic additives; powders characteristics; and paste properties

Silver-Palladium Thick-Film Conductors

A combined physics of failure and Bayesian network reliability analysis method for complex electronic systems

A novel fluxless bonding process of silicon wafer on molybdenum substrate is successfully developed. Si-to-Mo bonding can be used for packaging power devices, especially when a device consists of an entire wafer. 300 A Cr layer and 1,000 A Au layer are first deposited on Si wafers and Mo substrates. The Cr/Au dual layer is used as underbump metallurgy and seed layer of electroplating. To reduce plastic shear strain on the solder in a bonded pair, thick Sn layer (70 μm) is electroplated over Mo substrates having Cr/Au structure, followed immediately by thin (0.1 μm) Ag layer. This Ag layer acts as the capping layer to prevent inner Sn from oxidation. The bonding process is performed in 50 millitorrs vacuum to inhibit oxidation. The bonding condition is 290 °C for 15 min without the use of any flux. The bonding layer thickness is controlled at 50 μm by small spacers placed between Si wafer and Mo substrate. Microstructure and composition of the joints are studied under scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy (SAM) is also used to verify the quality of joints over the entire sample. Without using any flux, high quality and uniform bonding layer is achieved. The composition of the joint is more than 97 at.% Sn. No intermetallic compound layers exist in the joint. This novel fluxless bonding process should be valuable in packaging large high power devices.

Fluxless bonding of silicon wafers to molybdenum substrates using electroplated tin-rich solder

A fluxless bonding process between a 2" silicon wafer and a 2" x 2" molybdenum substrate with Sn-rich solder has been successfully developed. To achieve high quality joints, flux is avoided during bonding process. The flux or flux residues could be easily trapped in the joint, resulting in voids and uneven solder layer. Flux residues, if not completely removed, could also cause potential reliability problem. The key to carry out fluxless bonding is the oxygen-free environment during solder manufacture and bonding process. A thin Ag capping layer is electroplated immediately over the Sn layer after a thick Sn layer is electroplated on the Mo substrate with Cr/Au structure. This outer Ag layer prevents the inner tin from oxidation when the sample is exposed to air. The electroplated Mo substrate with Cr/Au/Sn/Ag structure is then bonded to a silicon wafer with Cr/Au structure in vacuum environment to suppress tin oxidation. Therefore, no flux is used. Microstructure and composition of the joints are studied under scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy (SAM) is also used to verify the quality of joints over the entire sample. Nearly void-free joints are achieved and the composition of the joints is more than 97 at. % Sn. The Sn-rich solder helps release the stress in a bonded pair and improves reliability of joints. The success of this development shows that it is indeed possible to bond an entire wafer to a different material by Sn-rich solder without using any flux.

Fluxless Bonding of Silicon to Molybdenum Using Sn-rich Solders

Molybdenum, which is widely used in the electronics industry, is usually a misunderstood metal. An introduction to its manufacture and present use is presented. The new development of cladding molybdenum with various materials and/or elements, which not only improves the reliability of the electronic device but also reduces production costs, is described.

http://ieeexplore.ieee.org/iel6/33/25259/01135607.pdf

Molybdenum in the Electronics Industry

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Molybdenum in the Electronics Industry