Temperature Humidity Bias Research Articles

Metal Migrations Outside the Package During Accelerated Life Tests

Various large-scale integrated (LSI) ceramic and plastic packages are stressed through different accelerated life tests including temperature, humidity, hostile gases, and bias. Migration phenomena are observed after biased tests, with metal dendritic growth from the cathodic pins and large corrosion areas around the anodes. When no bias is applied only corrosion areas which could affect any pin are evidenced. The metals found to migrate are Ni, Cu, Sn, and Ag. The influence of hostile gases proves dominant through solubility control in the anodically corroded areas. The effect of residual contamination on the substrates is also described. Physical failure mechanisms are investigated through the accelerated tests results and data from defective components in service conditions. It appears that silver migration is the main concern and that the use of Ag package technology should be severely limited. The temperature-humidity bias tests are more convenient to predict package life time in service conditions in order to provide a reliable quantitative evaluation.

Chip corrosion in plastic packages

The corrosion performance of both unencapsulated and plastic encapsulated parts has been studied under temperature-humidity-bias (THB) stresses using a patterned test chip with aluminum metallization. The effect of encapsulation materials and ionic contaminants purposely introduced on the chip surface has been determined for both accelerated THB and severe, real life conditions. Unencapsulated test chips exhibited very different THB performance characteristics from encapsulated parts including a near-zero induction time and a shallow post-induction slope on the % failures vs time curve. The induction time and mean-time-to-failure (MTF) for encapsulated devices were strong functions of both the polymeric class of encapsulant and the particular compound employed. At least part of the difference in performance between molding compounds has been attributed to impurities inherent in the compounds. Impurities contributed from conductive epoxies used for die attach also adversely affect the device's MTF, as do normal contaminants present on as-plated leadframes. The environmental factors of temperature, relative humidity and bias greatly affect the performance of encapsulated devices. In this study, the MTF decreased dramatically with bias between 5 and 30 volts, the range over which most devices operate. The acceleration factors relating device performance in an 85°C/85%RH environment to severe, real life conditions were surprisingly small and somewhat dependent on the encapsulant.

Silver Migration and the Reliability of Pd/Ag Conductors in Thick-Film Dielectric Crossover Structures

The relative performance characteristics of thick-film Pd/Ag conductors (0-34% Pd) for dielectric crossover structures in hybrid microelectronic circuits are described. The materials were supplied from Du Pont and Engelhard. The experiments involved waterdrop (WD) tests and temperature-humidity-bias (THB) tests at 90°C, 90% RH, and a dc bias of 5-50 V applied between the conductor electrodes for periods up to 1000 h. WD tests showed that the rate of Ag migration decreased by approximately 100 times as the Pd content in the conductor was increased from 10%-19%. However, the results of these tests were considerably scattered for electrodes of high Pd content. In addition, no conclusive results could be reached on the effect of the substrate or various encapsulants on the rate of migration. The rate of migration under THB conditions was considerably lower (10-4times) than that under the water-drop tests. Surface migration was found to be the dominant mode of failure in dielectric crossover structures. The rate of migration increased with the increasing voltage gradient. When the voltage was increased it caused an abrupt change in the capacitance and isolation resistance. The migration was more pronounced on the surface of bare alumina substrates than on substrates covered with a dielectric layer. Finally, a Du Pont 9137 glass encapsulant was found to be effective in preventing silver migration under THB conditions while an ESL 240 SB encapsulant enhanced the rate of migration.

New hybrid electronic molding compounds

This paper describes the performance characteristics of a new class of electronic molding compounds for semiconductor encapsulation. These new materials are identified as silicone-epoxy hybrid polymers. They were evaluated by testing integrated circuits molded in the hybrid system and comparing these results with those obtained with current state-of-the-art commercial silicone and epoxy molding compounds. Results are given for long-term life testing under environmental conditions of high temperature/high humidity and salt atmosphere. Temperature humidity bias data on linear integrated circuits tested by a semiconductor manufacturer are also presented. The effects of temperature and humidity on the molded plastic as measured by moisture absorption and dimensional stability are shown.