Reliability study of isotropic electrically conductive adhesives under thermal cycling testing

Abstract

Electrically conductive adhesives (ECA) have 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. However, other polymers can also be used. Currently, ECAs are increasingly used under demanding environments, inh which fluctuation of temperature is a common environmental stress. Such fluctuation causes stresses to form in the interconnections and are a common reason for failures in electronics devices. The interconnections formed with ICA are often not as mechanically robust as those with solders making it especially important to study how thermal fluctuations affect the ICA materials. In this work eight different commercial ICA materials were studied using two different thermal cycling tests. Additionally, low temperature tin-bismuth (Sn-Bi) solder was studied as a reference material. To study the behavior of the ICAs and the solder they were used to attach zero ohm resistors onto FR-4 test boards. After assembly testing of the samples was conducted in thermal shock and thermal cycling tests between -40°C and +125 °C. Marked changes were seen in the resistance values of the test samples during the test. Additionally, clear variation was seen between the ICAs. Apart from one ICA slow thermal cycling test was found to be more detrimental than the faster shock testing.