Investigation of adhesion strength of metallization on thermoplastic and ceramic substrates

One essential reliability criteria for Laser Direct Structured Molded Interconnect Devices is the adhesion between substrate and metallization. Low adhesion values are indicative of premature failure of the metallization and are often due to inadequate laser activation of the substrate. A measure of the adhesion is the force at which the metallization fails. Pull-off adhesion testing according to DIN EN ISO 4624 is used to assess the adhesive force between MID-substrate and metal layer. Besides thermoplastic LDS materials (LCP Vectra 840i LDS, TECACOMP® LCP LDS black 4107V, PEEK LDS black 3980, PPA LDS black 4108V), aluminum-nitride ceramic (Alunit®) plates were also laser-activated and metallized according to LPKF-LDS process. Furthermore 3D-printed plastic parts (PA2200 and PEEK), manufactured by Selective Laser Sintering (SLS) have been used. These SLS substrates are functionalized by coating with LPKF ProtoPaint LDS paint, which makes the plastic parts compatible to the LDS process. After IR-laser activation with LPKF MicroLine3D 165i system, the metallization is formed on the activated surface by electroless plating of copper, nickel and immersion gold consecutively. The adhesion strength of metallization was investigated by performing pull-off test of dollies with a shaft diameter of 2 mm. The pull tool for the 4 mm wide dolly head can easily be adapted to different bond testers. The copper dollies are lead-free soldered to the metallization. Due to the lower melting point of PA 2200, adhesive bonding was adopted to bond the dollies to the substrate metallization to reduce the bonding process temperature. This paper will investigate the influence of laser parameters such as laser power and scanning velocity on adhesion between metallization and LDS substrate.