Polymer films for laser-structured circuit carriers

摘要

Nowadays the most valued process to apply circuitries on Molded Interconnect Devices (MID) is the LPKFLDS (laser-direct-structuring) technology with an increasing amount of applications in various branches. Main advantage of this process is the high flexibility of laser processing three dimensional circuitries. Moreover, fine layout structures can be achieved by using a minimized laser spot. Therefore, the matrix polymer is filled with a special additive, enabling laser activation and sufficient metallization. To further improve the metallization quality and the coefficient of thermal expansion, high contents of inorganic fillers are added to the matrix polymer. However, this results in a low elongation at break, making the materials brittle. This is a major challenge especially for thin walls and films. In the present paper the potential for using films in combination with the LPKF-LDS process is considered for a use in flexible circuit carriers or for backmolding applications. Therefore, the content of talc in the polymer matrix is successively increased to determine the required minimum for appropriate metallization results. The compounds are extruded to films of different thicknesses. Using a Chill-Roll-Unit, one side of the films is smoothed. The films are structured, using different laser parameters and metallized, whereas these areas are investigated and evaluated using light microscopy and scanning electron microscopy. Furthermore, the plating thickness is measured as well as the roughness of the untreated samples. The metal deposition of the films is also compared to injection molded samples, especially regarding the surface structure. It can be shown, that an increasing amount of talc improves the plating thickness in contrast to poor metal deposition adding only LDS additive. The different surface structures of the Chill-Roll- Side and untreated side show no significant influence on the plating results. The achieved plating thickness seems comparable to injection molded parts of the same material.