Printed circuit boards for electronic applications are usually based on thermosetting materials to account for the brief high thermal exposure during the soldering process. In addition, such materials for electronic applications require the use of flame retardants, most often halogen-based additives, and must 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 intrinsically flame-retardant high-temperature thermoplastic foams. It is demonstrated that the foam cell morphology of polyetherimide as a suitable candidate as a matrix polymer depends on the processing conditions during the continuous extrusion foaming. Such thermoplastic substrates can be used in order to save weight, material and to reduce the production costs. It is shown that the resulting foam cell morphology and the foam density critically depend on the processing conditions. The influence of the extrusion temperature and pressure on the resulting foam morphology and properties are discussed. The compounding, foaming and fabrication of an A-B-A-sandwich with solid top layers and a foamed core was realised by a specially designed extrusion line.
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