Evaluation of process and anisotropy of thermosetting adhesives with ultraviolet-assisted 3D dispensing

Abstract

The use of 3D printing technologies enhanced with component placement and electrical interconnect deposition enables electronic systems with freedom in fabrication and complex embedded circuitry. However, with more electrical functionality being integrated, new material requirements become increasingly important. Well-established adhesive systems in electronic packaging have the potential to fulfill these requirements. This paper introduces a novel approach for processing adhesives with an extrusion-based UV-assisted 3D dispensing process. A specimen study revealed promising results for three out of six adhesives (denoted as A, D, E), for which an extensive anisotropy evaluation was performed: The relationship between the layered construction strategy and the material properties of the printed parts was characterized by micrograph analysis, tensile testing along with fracture analysis and laser flash analysis. An exemplary study for one adhesive via tensile testing showed no significant difference between three printing orientations. However, different construction strategies influenced the degree of anisotropy. The epoxy/acrylate (A) and polycarbamin system (D) showed higher strength and strain values when printed horizontally, indicating that the adhesive strength between the layers was not sufficient. The interlayer bonding for the epoxy system (E) was better due to the crosslinking between the layers. In addition, the evaluation of thermal anisotropy revealed a link between the thermal conductivity and the rate of the UV-curing for A and D. For material E, no significant difference was measured. The work presented in this article shows that dual-curing adhesives, in particular epoxy systems, are promising choices for additive manufacturing: It was possible to print fine geometries with good material properties and low anisotropy. These results are appealing since a wide variety of different adhesive systems is available. The findings serve to derive first design rules and provide a basis for further studies.