Current Loading of Adhesive Joints Aged in Environment with High Humidity

摘要

Electrical and mechanical properties of joints formed of electrically conductive adhesives change with external influences such as the temperature, humidity, mechanical stress, electrical current and many others. The goal of the work was to examine influence of short electrical current pulses of high intensity on adhesive joints before and after ageing in an environment with high humidity. The pulse width and frequency was set so that the joints were only minimally heated. Electrically conductive adhesive was based on bis-phenol epoxy matrix filled with silver flakes; silver concentration was 75% (by weight). Adhesive joints were formed by adhesive assembly of resistors with "zero" resistance (the real resistance was 14 mil) on a test PCBs. The boards made four point measurements of the joints resistivity possible. Humidity ageing was carried out at the 98% RH for 100, 200 and 300 hours. The rectangular current pulses with the width 5 μs, frequency 50 Hz and amplitude of 10 A, 20 A and 50 A were used for joints loading. It was found that the current pulses change the resistance of the adhesive joints. The resistance increased for the pulse amplitude 10 A and 20 A and for samples without ageing and aged for 100 and 200 hours. The resistance decreased for all samples loaded with the pulses 50 A. The percentage changes of the resistances were from 14% to (-37)%. The highest changes were found for the joints aged in humidity for 300 hours and for the highest pulse amplitude. It supports assumption about the increase of silver ions mobility in adhesive depending on moistening of the adhesive matrix.