Robert T. Howard

Creep and tensile behavior of lead-rich, lead-tin solder alloys

The tensile and creep deformation of a series of high lead solders with 2% to 10% tin over a temperature range of 0 degrees C to 100 degrees C is discussed. The yield strength is strongly influenced by the precipitation of the tin phase, which depends on temperature and tin content. The creep rupture behavior follows the Monkman-Grant relationship. It is found that the mechanical behavior during thermal cycling tests depends on cycle frequency and temperature range in a manner determined by the evolution of the precipitate microstructure. The tensile and creep test results reported are for simple, controlled thermal histories, which are not necessarily representative of cyclic conditions. It is apparent that the microstructure must be taken into account in evaluating the results of any plastic deformation experiments.<<ETX>>

Packaging Reliability-How to Define and Measure It

Microelectronic packaging employs many combinations of materials and processes to effect the interconnection of active and passive components and to provide interfaces with system levels of equipment. Reliability of these first-level packages is a key element in user acceptance and economics of electronic equipment. Complex interactions of design, materials, and processes may significantly affect package reliability. A tutorial approach to reliability methodology for first-level packaging as practiced in one company is presented. It emphasizes the identification of physical processes of degradation, approaches for mathematical modeling to relate accelerated testing to field application, and statistical quantification of unreliability (the complement of reliability). Application of this methodology is exemplified in the evaluation of several potential failure mechanisms discovered during the introduction of a new alloy for fiip-chip interconnection to the IBM packaging technology.

Electrochemical Model for Corrosion of Conductors on Ceramic Substrates

A quantitative model for electrochemical corrosion of conductors on microelectronic substrates was developed from fundamental principles such as Faradays and Ohms laws. The principal parameters are properties of electrode materials, geometry, and the surface resistivity of adsorbed moistured films. The time-to-fail calculation is linearly proportional to the surface (sheet) resistivity and inversely proportional to dc voltage between electrodes. Calculations based on data from published literature are presented as examples to illustrate the model. The relationship of surface resistivity to contamination of adsorbed moisture films by anions, primarily chlorides is discussed. Experiments are described in which surface resistivity is increased greatly by conformal coatings of polymers such as silicone junction coating and a polyamideimide. The silicone was shown to be superior because of its greater resistance to delamination from the substrate in high temperature and relative humidity (RH) exposures, due to higher bonding energies.