Giulio DiGiacomo

Metal Migration (Ag, Cu, Pb) in Encapsulated Modules and Time-to-Fail Model as a Function of the Environment and Package Properties

Metal migration occurs between biased lands and, under conditions conducive to electrocrystallization, causes dendritic growths and failure. A model, based on the physics of condensation, ionic migration and thermally activated mechanism, was verified with polymer-encapsulated modules (Ag lands) under accelerated conditions of temperature, humidity and voltage. The acceleration factors agree with the predictions. Additional results with Ag, Cu, Pb films showed that oxides and process contaminants constitute strong migration factors controlling passivation against the electrochemical process.

Current-Leakage Kinetics Across Tinned Cr/Cu Lands Having Epoxy Overlay

A leakage current between Cr/Cu conductors on a ceramic vehicle coated with an epoxy layer is described. The leakage is measured under stress conditions of temperature, relative humidity (RH), and voltage. A model is developed to project the leakage results to field conditions as a function of the stress, gap, and diffusion properties.

AuAgPd Ternary Alloy for Thick-Film Electrodes

A new thick film paste composition that eliminates the possible formation of free silver when exposed to high Pb, Pb-Sn solders is described. When reacted with Pb--Sn solder in the molten state, the ternary Au-Ag-Pd, while still subject to palladium depletion, is shown to yield an AgAu alloy. The resulting AgAu alloy is more resistant to sulfur corrosion than the pure silver it replaces. Studies revealed that with increasing Au content, the rate of sulfide attack decreased. In addition the type of corrosion also changed dependent upon temperature and sulfur concentration. At higher temperatures (125°C) and saturated sulfur concentrations (104ppb), a mixed Ag and Au sulfide forms, whereas at lower temperatures and lower sulfur concentrations (e.g., 30°C and 10 ppb) only silver sulfide forms. These results are discussed in relation to the noble alloying element protection model of Wagner.

Reliability of Die-Level Interconnections

At the die level, solder interconnections can fail by a number of failure mechanisms if the stress conditions are severe; i.e., fatigue, corrosion, metal migration, electromigration, creep, and thermomigration. Under normal field conditions, non-encapsulated open-array flip chip solder joints attached to alumina chip carriers exhibit the best reliability in the field among all interconnect methods. This, of course, is the result of following established design rules, process parameters and having a firm understanding of the reliability factors associated with flip chip interconnects. Many of these reliability factors are discussed in this chapter. It is necessary to establish an accelerated test capability so that a relatively long life in the field can be predicted on the basis of short term tests. The validity of the tests is achieved by verifying established semi-empirical models and characteristic parameters, and then are employed to predict the field life of joints.

Phosphorus Migration Kinetics from PSG to Glass Passivation Surface

The diffusion of phosphorus through chip glass passivation is studied at various temperatures and water vapor pressures. The phosphorus diffuses from the phosphosilicate glass (PSG) to the glass surface through defects. It is detected by electron microprobe at low accelerating potential (3¿ kV) to avoid excitation of the underlying PSG. The amount of phosphorus transported varies proportionally to the water vapor pressure with an activation energy of 0.32 eV.