Accelerated life test of Z-axis conductive adhesives

The success of coarse-pitch applications of conductive particle-filled adhesives has increased the interest in using such adhesives in fine-pitch applications, such as flip-chip on-board interconnection. Since these materials contain metallic particles to conduct currents in the z-direction (i.e., perpendicular to the plane of circuit board), their propensity for metal migration is a concern. Accelerated temperature, humidity and bias (THB) tests have been applied to a group of materials designed for fine-pitch applications. The accelerated life test conditions were 85°C/85% RH at three different voltages: 10 V, 50 V, and 100 V. The studies were focused on the samples´ time-to-failure as well as the associated conduction and failure mechanisms. The test results showed significant metal migrations, and enhanced electric field stresses (10² to 10 ⁴ V/mm) are proposed as the driving force for failures