DEVELOPMENT OF AN ENVIRONMENTALLY FRIENDLY THERMOPLASTIC PRINTED CIRCUIT BOARD MANUFACTURED BY FOAM EXTRUSION

摘要

In general, printed circuit boards for electronic applications are based on thermosetting materials due to the brief exposure to high temperatures during the soldering process. These materials require the use of flame retardants and must often be treated as hazardous waste due to the toxic nature of these additives. Thus, a procedure was developed in order to continuously manufacture novel printed circuit boards made of an intrinsically flame-retardant high-temperature thermoplastic foam. Such thermoplastic substrates are foamed with halogen-free blowing agents in order to save weight and material and to reduce the production costs. However, the foam cell morphology of polyetherimide as a suitable candidate polymer critically depends on the processing conditions during continuous extrusion foaming. A small average cell size and a homogeneous cell size distribution especially for the application of such foamed substrates cannot be achieved by a variation of the processing conditions only, suitable nucleating agents are required even when using chemical blowing agents. Nevertheless, the compounding, foaming and fabrication of an A-B-A sandwich with compact surface coatings and a foamed core were realised by a specially designed extrusion line. These extrudates are suited as a substrate for printed circuit boards, especially where a continuous usage at elevated temperatures is required and for high-frequency applications.