Reliability of isotropic electrically conductive adhesives under condensing humidity testing

Abstract

Electrically conductive adhesives (ECA) are considered to be one of the future technologies due to their potential for low cost, high reliability, and simple processing. Additionally, an important advantage with ECA materials is the possibility for low bonding temperature. Therefore, they are especially well suited for low cost applications. ECA materials are prepared by mixing polymer matrix with electrically conductive particles. In isotropic conductive adhesives (ICA) concentration of the conductive particles is high and they conduct in all directions. Several materials can be used to manufacture ICAs. The most widely used ICAs in the electronics industry are silver-filled epoxies, which also provide a high level of thermal conductivity. However, other polymers can also be used. All polymer materials used in ICAs absorb moisture, which affects their mechanical behavior. Additionally, the electrical properties of the ICA may change. Therefore it is important to study how different ICA materials behave under humid conditions. Especially, if the humidity levels are high, these changes may occur very rapidly. In this work 14 different commercial ICA materials were studied under condensing humidity conditions. To study the behavior of the ICAs they were used to attach zero ohm resistors onto FR-4 test boards. To study the effect of glob top on the behavior of the ICAs, two additional test series were assembled with two epoxy ICAs using a glop top material to protect the components and the interconnections. Marked changes were seen in the resistance values of the test samples during the test. Additionally, considerable variation was seen between the ICAs. Some ICAs showed increased resistance values very quickly after the testing was started. The two ICAs not shown did not show failures during testing.