Effect of non-conducting filler additions on anisotropic conductive adhesives (ACAs) properties and the reliability of ACAs flip chip on organic substrates

Flip chip assembly on organic substrates using ACAs have received much attention due to many advantages, such as easier processing, good electrical performance, lower cost, and low temperature processing compatible with organic substrates. ACAs are generally composed of epoxy polymer resin and small amounts of conductive fillers (less than 10 wt.%). As a result, ACAs have almost the same CTE values as an epoxy material itself, which are higher than conventional underfill materials which contain lots of fillers. Therefore, it is necessary to lower the CTE value of ACAs to obtain more reliable flip chip assembly on organic substrates using ACAs. To modify the ACA composite materials with some amount of conductive fillers, non-conductive fillers were incorporated into ACAs. In this paper, we investigated the effect of fillers on the thermo-mechanical properties of modified ACA composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. For the characterization of modified ACAs composites with different content of non-conducting fillers, dynamic scanning calorimeter (DSC), and thermo-gravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), and thermomechanical analyzer (TMA) were utilized. As the nonconducting filler content increased, CTE values decreased and storage modulus at room temperature increased. In addition, the increase in the content of filler brought about the increase of Tg^DSC and Tg^TMA. However, the TGA behaviors stayed almost the same. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. It was observed that reliability results were significantly affected by CTEs of ACA materials, especially in the thermal cycling test. Results showed that flip chip assembly using modified ACA composites with lower CTEs and higher modulus from loading non-conducting fillers exhibited better contact resistance behavior than conventional ACAs without non-conducting fillers